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THE UNITED REp· Lie OF TANZANIA MINISTRY OF W DEVELOPMENT.
ENERG ,f!.A~Ii~n;, iN'ERALS .;;r'
J.V~"I!E'l.L< Bf),NK FOR DEVELOPMENT
:( .. ~ > • •
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TABORA'~;:,REGION WATER M'(ST~ER PLAN
FINALBEPORJ VOLUME 6:1'
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HYDROGEOLOGICAL STUDIES "I'
PER SUNDB~:RGS'vt
CHAPTER 1: 1. 1 : 1.2:
1.3: 1.4:
1.5: 1.6:
CHAPTER 2:
2.1 : 2.1.1 : 2.1.2:
2.1.3:
2.1.4:
2.2: 2.2.1 : 2.2.2:
2.2.3:
2.2.4:
CHAPTER 3:
3.1 :
3.2: 3.3:
3.4:
VOLUME 6
TABLE OF CONTENTS
Introduction
HETHODOLOGY Studi es of Maps Inventory of Existing Ground Water Re-sources, Boreholes and Shallow Wells
Geophysical Investigations
Dri lling Studies of Representative Areas
Control of Ground Water Levels
REPRESENTATIVE AREAS
Introduction • Tumbi Representative Area Geophysical Investigations
Dri 11 ings Summary of the Ground Water CondHions in Tumbi Representative Area Computer Maps of Tumbi Representative Area Nata Representative Area Geophysical Investigations
Dri 11 i ngs Ground Water Conditions in Nata Representative Area Comment on the Extracts from the Computed Maps; Nata Representative Area
GROUND WATER POTENTIAL IN TABORA REGION
I ntroduct ion Aquiferous Properties of the Hydrogeological Units Relevant to Deep Boreholes Control of Ground Water Levels Deep Ground Water Potential Estimates
Geological and Hydrogeological Report on Shallow Dug Wells
PAGE
1
2 2
3
4 4
10 10
14
16 25 48
71
76
81
86
100
131
136
139
141
145 154
185
3.5:
3.6:
CHAPTER 4: 4.1:
4.2:
4.3:
Pumping Test Methodology, Shallow Wells Shallow Ground Water Potential Estimates
HYDROGEOLOGICAL INVESTIGATIONS Organization and Conduct of Resistivity and Magnetic Surveys Operation of a Seismic Team Recommendations for Drilling Operations
Appendi x 6.1 Village List. Computed Yields (Maximum) within a 3 km Circle about the Village Centre
Appendix 6.2 Result of Shallow Well Inventory
PAGE
191 196
207
211
212
11
..If
b I1
11
,I
11
:1
I I I I
I
I I
LIST OF TABLES VOL. 6
Table 6.1: Boreholes in Tabora Table 6.2: WMP Deep Boreholes in Tabora Region Table 6.3: WMP Shallow Boreholes in Tabora Region
Table 6.4: Boreholes Logged During the WMP Table 6.5: Velocity Estimates Profile 6-203
Table 6.6: Velocity Estimates Profile 6-204 Table 6.7: Ground Water Levels in Tabora Region
Controlled Boreholes Table 6.8: Aquifer Properties of Investigated Geological
Units in Tabora Region
Table 6.9: Table of Parameters for Estimating Ground Water Potential
Table 6.10: Yield at Varying Recharges Table 6.11: Yields of Exisiting BH and WMP-BH Table 6.12: Parameters Derived from the Shallow Well
Inventory in Tabora Region Table 6.13: Results of Depth Calculations; Shallow Wells Table 6.14: Control of Permeability Estimations; Shallow
Wells
Fig. 6.1:
Fig. 6.2:
Fig. 6.3: Fig. 6.5:
Fig. 6.6: Fig. 6.7:
Fig. 6.8:
Fig. 6.9:
Fig. 6.10: Fig. 6.11:
LIST OF FIGURES VOL. 6
Boreholes in Tabora District (A) Boreholes in Nzega and Igunga Districts
Boreholes in Urambo District
Location Map Representative Areas View Towards the Northern Part of Tumbi Basin Granite Outcropping in the Southeastern Part of Tumbi Basin
View Towards West at the Site of Resistivity Profile 6-104
View Towards West Along Resistivity Profile 6-105 Topographic Map of Tumbi Representative Area
Special Map 1:10000 Showing Profile and BH Sites, Tumbi Basin
PAGE
3
5
6
9
38
40
146
153
161 164 168
199
200
201
11
12 13 15
17
18
20
21 23
24
Fig. 6.12:
Fig. 6.13:
Fig. 6.14:
Fig. 6.15:
Fig. 6.16:
Fig. 6.17:
Fig. 6.18: Fig. 6.19: Fig. 6.20: Fig. 6.21: Fig. 6.22:
Fig. 6.23:
Fig. 6. 238 :
Fig. 6.24:
Fig. 6.25: Fig. 6.26:
Fig. 6.27: Fig. 6.28:
Fig. 6.29: Fig. 6.30:
Fig. 6.31:
Fig. 6.32:
Fig. 6.33:
Fig. 6.34:
Fig. 6.35:
Fig. 6.36:
Resistivity Profile 6-104 Magnetic Profile 6-304 Resistivity Profile 6-105 Magnetic Profile 6-305 Resistivity Profile 6-106 Magnetic Profile 6-306 Resistivity Profile 6-112 Magnetic Profile 6-313 Resistivity Soundings 6-414-416 Resistivity Profile 6-124 Magnetic Profile 6-332 Seismic Profile 6-203 Seismic Profile 6-204 Magnetic Profile 6-307 Soil Analysis for BH 5-206 A Augering with the Borros Drilling Machine at 200 m in Profile 6-105 (BH 5-401) Pulling up the Rods. Augering at 200 m BH 5-401 in Profile 6-105 Percussion Drilling and Sampling at BH 5-310 Profile 6-124 Results from Drilling of BH 5-310
Rig 53 Drilling BH 5-201 in Tumbi Basin Soil Analysis for BH 5-201 (138/78)
Soil Analysis for BH 5-209 (186/78)
Boreho1e Record BH 5-106 (106/78) Soil Moisture Measurement at 5-404 Tumbi Basin Simplified Picture Showing Ground Water Conditions in the Upper Part of Tumbi Valley
Precipitation and Ground Water Levels in Tumbi Representative Area Ground Water Variations during One Year in BH 5-106 The Flat Basin of Nata Representative Area
View Towards Northwest from the end of Profile 6-108 Extract from Geological Degree Sheet 28 Nzega NW Quarter Topographic Map of Nata Representative Area
PAGE
26
28
30
32
34
36
39 42 45 51
52
53
55
56
58
59 60
64 70
73
74
75 81
82
83
84
'I
I I I I I I I I I I I I I I I
Fig. 6.37:
Fig. 6.38:
Fig. 6.39:
Fig. 6.40:
Fig. 6.41:
Fig. 6.42: Fig. 6.43:
Fig. 6.44: Fig. 6.45: Fig. 6.46:
Fig. 6.47: Fig. 6.48: Fig. 6.49:
Fig. 6.50: Fig. 6.51:
Fig. 6.52:
Fig. 6.53: Fig. 6.54:
Fig. 6.55: Fig. 6.56:
Fig. 6.57:
Fig. 6.58:
Fig. 6.59:
Fig. 6.60:
Special Map 1:10000 Showing Profile and Borehole Sites, Nata Basin Resistivity Profile 6-107. Magnetic Profile 6-308 Resistivity Measurements at 600 m in Profile 6-108 Resistivity Profile 6-108. Magnetic Profile 6-309 Resistivity Profile 6-109. Magnetic Profile 6-310 Resistivity Soundings 6-406-11
Seismic Profile 6-205
Seismic Profile 6-206 Rig 48 Drilling BH 124/78
Borehole Record 107/78 Borehole Record 124/78 Borehole Record for 5-210 (190/78)
Borehole Record for 5-317
Borehole Record 125/78 Borehole Record for 5-211 (191/78)
Borehole Record for 5-314
Borehole Record for 5-318 Borehole Record for 5-316
Borehole Record for 5-315 Soil Moisture Content vs. Depth at BH's 5-413, 414, and 415. Nata Representative Area Simplified Picture Showing Ground Water Conditions in the Central Part of Nata Representative Area Precipitation and Ground Water Levels in Nata Representative Area Contour Map Shallow Ground Water April 1979 Control of Ground Water Variations in Deep Boreholes; BH 66/78, 67/78, 68/78
PAGE
85
87
89
90
92 94 96
98 101 105 109 111
112
117
122 123 124 126 128
130
133
134 135
148
Fig. 6.61: Control of Ground Water Variations in Deep Boreholes; BH 105/78, 106/78, 124/78 149
Fig. 6.62: Control of Ground Water Variations in Deep Boreholes; BH 125/78, 137/78, 144/78, 7/78 150
Fig. 6.63: Control of Ground Water Variations in Deep Boreholes; BH 3/69 151
Fig. 6.64:
Fig. 6.65: Fig. 6.66: Fig. 6.67:
Fig. 6.68:
Fig. 6.69:
Fig. 6.70 Fig. 6.71
Fig. 6.72 Fig. 6.73: Fig. 6.74:
Fig. 6.75:
Fig. 6.76:
Fig. 6.77:
Fig. 6.78:
Fig. 6.79:
Fig. 6.80:
Fig. 6.81:
Fig. 6.82: Fig. 6.83:
Fig. 6.84:
Fig. 6.85:
Fig. 6.86:
Fig. 6.87:
Steady Flow to a Well Penetrating an Uniform Recharged unconfined Aquifer Yield vs. Permeability; Geology Class 7
Yield vs. Well Diameter Diagram Showing the Relationship between Yields from Airlifts and Yields Calculated from Lithology Diagram Showing the Relationship between Oy and O2 (see text) Diagram Showing the Relationship between Oy and 01 and 03 (see text) Region Map Computed Yields District Map Igunga and Nzega Computed Yields
District Map Urambo Computed Yields District Map Tabora (north) Computed Yields
District Map Tabora (south) Computed Yields Typical Cross Section of Shallow Well in the Filled Valleys - Alluvial Deposits Typical Cross Section of Shallow Well in the Laterite and Lateritic Soils (deep soils)
Typical Cross Section of Shallow Well in the Residual Soils (deep) Typical Cross Section of Shallow Well in the Shallow Residual Soils (less than 5 m) Ground Water Fluctuations (shallow wells) Steady Flow to a Well Partly Penetrating an Unconfined Aquifer Comparison between k-va1ues Geology Class 1 Comparison between k-va1ues Geology Class 3
Comparison between k-va1ues Geology Class 7-8 Resistivity Team Taking a Reading on the ABEM Terrameter Checking the Samples Rig 48 Drilling at Nyandekwa Well Testing of BH 106/78; Tumbi Representative Area Checking the Draw-down. Aquifer Test of BH 106/78;Tumbi Representative Area
PAGE
156
163
165
170
171
172 174
176 179 182
183
187
187
188
188
195
198 203
204 205
210
215
216
217
I1
VOLUME 6
HYDROGEOLOGY
INTRODUCTION
This volume deals with the hydrogeological work carried out during the Tabora Region Water Master Plan. There was a field work phase described in Chapter 1 followed by an intensive analysis of the data. The results of this work are presented in this volume. The geology of the region is presented in Volume 8 together with the results of the photo interpretation etc.
The methodology of the hydrogeological work is described in Chapter 1. Chapter 2 gives a description of the two representative areas studied during the project, investigations performed and results recorded. The hydrogeology of the region is discussed and ground water potential assessed in Chapter 3. Finally practical recommendations for hydrogeological investigations and drilling are given in Chapter 4.
In volume 6A the detailed drilling results are given. The geophysical investigations are reported in Volume 7. Data on springs are given in Volume 8.
The exploitation of ground water is the key to the development of Tabora's water resources. Surface water sources are expensive and limited. Use of ground water is complex and requires systematic investigation, record keeping, and analysis. What is presented here is the beginning of work on Tabora's ground water resources.
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. 1. 1
CHAPTER 1
METHODOLOGY
The field investigation program for the study of the hydrogeology has been performed in two phases:
I II
Collection and study of available data. Collection and study of new data.
Fo 11 owi ng these phases ana lys i s of the results, has been performed'.
The Phase I comprised the following steps: .j'i'(':R',' . 1. Study of the aerial photos, topographicinaps:;,and .. geologi:; ....
ca 1 .. maps .. 'i'" ."," ,., .,,'. ' .• ·"'~~t~;f:~~~f¥C\~':~W:;,1;i;Hf.'(····· 2. Study of existing ground water sources, sUch',asbOreholeS
and shallow wells. . .
Using the results of the studies during Step 1 the field work in Phase 11 could be planned and carried out. This part could be divided in four steps:
1, Geophysical investigations. 2. Drilling, well-logging, well testing. 3. Studies of representative areas. 4. Control of ground water level.
We now review the work that was carried out in the field along the above lines.
PHASE I COLLECTION OF AVAILABLE DATA
Studies of Maps
The region is largely by contour maps of the scale 1:50,000 prepared in the last five years. Only southermost part, south of the 6th latitude lacks coverage. Aerial photos of the scale about 1:50,000 and from the period 1974-75 cover the same area as the contour maps. However, older photographs exist which partly fill the gap and they have been used for completing the maps drawn for the project. For the hydrogeological analysis these photographs are adequate.
The interpretation of the aerial photographs comprised geology, seepage zones, land use and land forms, all of which are described and commented upon in Volume 8.
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On the basis of the map studies complemented with fi i nves ti gati ons geo 1 ogi ca 1 maps were completed for the",four',,; districts as well as a structure map showing the main';l.in~aments and dislocation zones. The geological part gives adescHption of the bedrock and overburden. Us i ng thi s i nformati on';the, , selection of suitable sites for the field work was done":l~e. siting of geophysical profiles and drilling locations a; well as selection of representative areas. ""
Inventory of Existing Ground Water Resources, Boreholes ' and Shallow Wells
An inventory of existing deep boreholes was carried out based upon the borehole files at the MAJI office in Tabora town and at Dodoma. According to this inventory 129 boreholes have been dri 11 ed i n Ta~ora as re~orded i ~ the records, but of;. thes~;,only 52 could be dlscovered ln the fleld. Most of the boreholes,were found in the Urambo District and very few in the Igunga District . A summary is given in the table below and the locations and a more thorough description of the boreholes is given in Volume 6A.
The use of boreholes for water schemes is given in Table 6.1.
TABLE 6.l. BOREHOLES IN TABORA
District Total No. Included in or Designed for Schemes Existing Under Construction Designed
Urambo 24 8 1 2 Tabora 9 2 4 0 Nzega 10 4 1 0 Igunga 5 1 0 0
Total 48 15 6 2
A similar inventory of the shallow wells WdS carried out and the geology team here cooperated with the engineering and the village survey teams. The results of this field work is shown in Volume 3 Chapter 5, and Volume 38.
In all 163 shallow wells were inventoried and out these wells 80 were selected for the control of the water table during the project. A map showing the location of the wells is presented in Volume 3 (Chapter 5).
1.3 , i ,
1.4
4
PHASE II COLLECTION OF NE\< DATA
Geophysical Investigations
The geophysical survey comprised 30 resistivity profiles, 30 resistivity soundings, 13 seismic profiles and 50 magnetic profiles. The siting of profiles was based upon the aerial photo interpretation and field checks. The results of all of this geophysical work are described and commented upon in the Volume 7.
Dri 11 i ng
The drilling was performed by using two rotary drilling rigs, one Schramm Rig (No. 48) for deep boreholes and one CME Rig (No. 53) for shallow boreholes. Both the rigs belong to MAJI and were run by MAJI staff.
Additional drillings of shallow boreholes with small diameter were carried by using a Borros Rig. The rig was used for completing the investigations mainly in the representative areas as well controlling the lithology at some of the shallow wells and at the sites of the resistivity soundings. The advantage of this equipment is that it is possible to take undisturbed samples during the drilling and to set pipes for soil moisture -measurements and control of shallow ground water levels.
The drilling of deep boreholes started during May 1978 and continued to the end of April, 1979 and in all 23 completed boreholes were drilled. Due to delays of the transfer of the 01E rig to the project the work with this equipment did not start before October 1978 and continued until early May, 1979. The rig drilled 25 shallow boreholes usually in addition to the deep boreholes in resistivity and seismic profiles but also to investigate the sites of shallow wells. All the boreholes drilled are listed in the Table 6.2 and Table 6.3
During drilling of deep boreholes the penetration rate was recorded. A short description of the usefulness of this information is given below.
During the drilling, samples of the overburden and the bedrock were collected every 1.5 m (5 ft), and analyzed on the site or at project office in Tabora Town.
Hhen wa ter was struck wa ter samp 1 es from the boreho 1 es were taken and sent for analysis at the water laboratory at MAJI, ~1wanza. When sufficient water inflow was noted during the drilling of
.~
.,-102 , 7/78 '. 5-103
;B(78
_5-104
, 105(78 5-105
,06(78
"5-106
107(78 5-107
...•... ;~ 124(78 5-108
.25(78 .5-109 .. 137(78
5-110
1'44(78 . 5-111
148(78 5-112
~1160(78 , 5-113
·64(78
r-114
~ 169/78 . 5-115
1181178 15-116 ,. ..
, 1(79 5- 117
~110179 "fi, 5-118
.15179
,··t5-119
'i ::( 4/79 , 5-120
'2179 -121
f179 -122
8179 J-123
I I I I I L
TABLE 6.2.
1J~P 1 ~~~e50( Location
118/2 Kipalapala
98/4;118/2 Uramba
98/4; 118/2 Uramba
98/3 Kapande
98/3 Kalunde
118/1 Tumbi
80/1 Nata
801l Nata
80(1 Nata
80(2 Ziba
80/2 Ziba
81/3 Nyandekwa
- Sakamal ;wa
65/4 Kininginila
81/2 ~lbutu
80(4 Ul aya
80/4 Nkinga
I 80/1 Kitangil i
80(2 I bo logero
80/2 Ibologero
80(2 Ibologero
80(2 I bo 1 ogero
137/1 Mkolye
137 (1 Sikonge
District
Tabora
Tabora
Tabora
Tabora
Tabora
Tabora
Nzega
Nzega
Nzega
Igunga
Tgunga
Igunga
Igunga
Igunga
Igunga
19unga
Igunga
Nzega
Igunga
Igunga
Igunga
Igunga
Tabora
Tabora
WATER M~STER PLAN
DEEP BOR£HOLES
TA80RA REGION
RIG 48 SCHRAMM
Location I Level in M:A.S.L. utm Top casing Ground
(TC) (GL)
4775 94371 1199.6 1199.0
4740 94472 1170.73 1170.21
4741 94472 116B.53 1168.22
4701 94400 1173.33 1172.63
4662 94504 1140.7 1140.1
4675 94402 1167.06 1166.31
5153 95491 - 1151.0
5153 95491 1151.52 1151.00
5152 95489 1153.57 1153.22
5407 95331 1199.7 1199.1
5408 95331 1199.1 1198.5
5613 95 301 1177.8 1177.2
6152 95504 1051.1 1050.5
6036 95596 1060.6 1060.0
5996 95319 - 1070.0
5453 95 162 1244.3 1244.0
5483 95 126 1272.6 1272.0
5258 95 345 1188.2 1187.6
5524 95324 1212.3 1211 .7
5522 95323 1207.4 1206.8
5522 95323 - 1206.8
5522 95323 1207.0 1206.4
4680 93860 1146.8 1146.2
471 0 93820 1142.6 1142.0
loepth ~ Water ~ m level Remarks
m m ~:; 1 \~s; 90.5 2.1 - - Obstruction at 15 m.
note 10/7/78
50.3 21.0 4.6 (1 . 1 ) Caving in obstruction, 1.2 40 m. note 28/11 {78
67.7 21.0 4.4 - Caving in obstruction, 29 m. note 28/11 /78
59.5 22.6 8.2 (0.7) 30.2
90.5 - 30.5 -98.8 21.0 14.0 (1. 1 )
0.5
69.2 38.7 - - Caved in during drill-50.9 109, slightlY salty
water . 53.9 39.3 1.1 (2.3) No well test drill
site flooded. slightly salty water.
63.1 16.5 0.8 (4.0) 41.8 4.0
90.5 - 24.9 -
58.5 43.3 25.3 -54.6 57.6
90.5 31. 7 20.0 (2.0) No well test, wet conditions
91. 1 16.5 7.0 - Salt water caving in c,. obstruction at 41.8 m.
82.0 16.5 8.6 - salt water caving ;n obstruction at 52.0 m.
21.0 - - - Abandoned, break down of engine.
82.0 37.8 - - Caving in obstruction, 40.8 40.8 27.7 m
46.3 46.3 73.8 5.8 2.5 03.0) -
21.0 6.8
90.5 18.2 3.1 . ( - ) -0.6
85.3 8.2 2.8 (0.9)
118.6 7.3 0.9 - Caving in 35.7
20.0 - - - Caving in
34.2 5.8 0.6 ( - ) Production hole 19.4 5.7
58.5 13.4 34.0 - -
37.2 1.2 1.2 - -
1orehole I Wf1P I Map Village !~umber No Sheet No
I :1 :50.000
138/78 i 5-201 i 118/1 TUlnbi , 118/1 139/78 I 5-202 I Tumb; ,
140/78 1 5-203 i 118/1 Tumb; , I
/ . , ! 118/1 Tumb;
I .
15.204
, 118(1 Tumb; , 179/78 I 118/1 Tumb;
I I 5-205 180/78 118(1 , Tumb; , 183/78 A i 5-206 A • 118(1 Tumb; , , 183/78 B j! 5-206 B 118/1 Tumb; I : 184/78 : 5-207 118/1 Tumb; 185/78
, 5-208 118(1 Tumb; ;
- 118/1 Tumb;
186/78 : 5-209 118/1 Tumb;
190/78 ,
5-210 80(1 Nata
191/78 5-211 80(1 Nata
16/79 5-212 80/1 Nata
17/79 : 5-213 80/1 Nata
18/79 5-114 80/1 Nata
Kitang il i I 19/79 5-115 80/1 47/79 .5-216 80(1 :Kitangili!
48/79 5-217 80/4 Nkinga I ;
49/79 5-218 81/3 Nyandekwa I 50/79 5-219 81(3 Nyandekwa) 51/79 5-220 81/3 Nyandekwal , 52179 .5-221 80/2 Zl ba
5-222 80(2 Zi ba 5-123 80/2 Ziba 5-214 99/3 Igalu1a 5-225 99/3 Igalula I
TABLE 6.3.
~IATER MASTER PLAN
SHALLOW BOREHOLES TABORA REGION
RIG 53 CME
District I Location Level in m.a.s.l. Depth I UTM Top casing Ground (m) (T.C. ) (G.L. )
Tabora i 4675,94402/ 1166. 76 1 1166.06 22.3
Tabora 4675,94402 1166.91 1166.14 19.8
Tabora 14675.944021 1167.01 I 1166.11 22.9
Tabora ,4675,94402 I . i 1166.1 10.0 Tabora , 4675 ,94402 I . , 1166.1 10.7 I Tabora !4675.94402 ! 1166.43 I 1166.31 22.3
14675,944021 I Tabora 1166.53 1166.21 19.2
Tabora ! 4677 , 94419 i 1171.0 14.0 Tabora i 4677 , 94419 i 1171.84 ; 1171.0 32.0 Tabora i 4682,94417 i 1173. 97 1 1173.32 10.4 Tabora i 4687,94415 I 1203.44 1 1201.48 I 16.8 Tabora i4679,944021 - 1175.2 6.1 Tabora i 4679,94402 i 1176.43 1175.63 14.6
j f Nzega ,5155,95492 I
! 1151.83 1151.06 45.7
Nzega : 5153,95486 i 1154.00 1153.07 38.7 : Nzega j 5153,95486 ! 1153.64 : 1153.32 35.5
1159.26 : Nzega '5157,95484 , 1158.57 33.5 , . Nzega • 5156,95484 1156.52 , 1156.02 44.2 Nzega .5258,95345 1188.1 1187.6 26.5 Nzega 5261,95345 1197.8 1197.5 33.5 Igunga 5483,95126 1171.7 : 1271.8 11 .3 Igunga i 5613,95301 - 1177.1 30.5 Igunga .5614,95301 1174.4 1173.8 23.8 I
, 5615,95301 ,
Igunga 1180.6 1180.0 25.9 I Igunga .5452,95317 1256.0 1255.3 16.8
Igunga 5452,95316 : 1252.7 1252.0 9.7 Igunga 5443,95317 1148.5 1247.8 4.6 Tabora 5110,94582 ' 1230.2 1230.0 12.2 Tabora 5110,94582 1230.3 1130.0 11.9
\~ater Water ! Yield REMARKS Struck Level : (m3/h)
Caaing (m)B.G.L (m)B.T.c.1 Genera 1
21.6 14.7
I · Obstruct i on 1"
13.9 16.8 · Obstruction 1"
20.7 17.3 · 2"
· I : I · No casing
· · No casing
19.8 1
10.0 · 1"
I 19.2 12.3 I
I 1"
I · 1
I · No casing
12~.0 25.9 -
I 2"
I · 11.0 - 2" I I · 12.0 - 4"
- I . I I No casing 4.6: 10.7 I 3.0 I ·
I 2"
1.R I
24.4 I I · 4"
1.5:7.6 1.0 · I 4" I
12.2:24.4 0.7 ! - i 2"
I ! 13.7:24.4 3.2 , - i 2"
13.7:24.4 - ! - I 2" I I
6.4 : 19.8 · , 1" : , 24.4 : 13.7 - ;
2" i 6.1 2.0 ; - I
1" , - - 1 No caSing - -
, 2" : ,
- ; 2" , 5.0 2"
1.5 3.0 2" 1.5 2.4 1" 9.1 4.6 4"
9.1 6.1 4"
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I
I
I
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I
7
deep borehole. If the result was promising it was followed up by a well test (see below).
The locations of the WMP boreholes and the existing boreholes are presented on the three di s tri ct maps, Fi gures 6.1. - 6.3.
In many cases the sub surface conditions and lithology of the deep boreholes were investigated with a well log unit consisting of SP, resistivity, gamma and temperature logs. The results of these logs are given in Volume 6A with the other borehole data.
~~Q~!!:~!!.QQ_B~!§
The drilling method used with the Schramm Rig can only provide dispersed samples of soils and rock chips blown up to the ground surface during the drilling. The accuracy of the analysis of the samples depends upon the representativity of the material collected which naturally, with this type of sampling, can be doubtful particularly in transition zones between gravel and bedrock, weathered boulders and weathered bedrock etc. However, record of the penetration rate assists in the interpretation of the lithology. For the correlation of penetration rate and lithology, the type of drill bit used must be noted as well as any changes of drill bit, whether one or two compressors are used, and if there are noticeable changes of pressure on the bit etc. When drilling through the overburden, i.e. loose material, usually a drag bit was used. After striking bedrock the bit was changed and the drilling continued with either a roller bit or cross bit. The penetration unit used was number of minutes per 1.5 m i.e. the length of time required for collecting one sample.
We 11 Tests
Deep Boreholes. The well test unit, which was supplied by the Ministry but had been developed by the Consultant on another project, consisted of two submersible pumps, one Ritz type 6666-16 of maximum capacity, 25 m3/hr at a lifthead of 100 'U and one DEBE pump with maximum capacity 5 m3/hr at 40 m 1 ifthead. The big pump had several breakdowns so the small pump was used for most of the tests: The pumps were mounted on a truck fitted with a mast, a wiredrum and a generator driven by a diesel engine. Unfortunately the electrical part of the unit had several breakdowns which seriously delayed the program. At a few boreholes the site proved inaccessable to the truck because of very wet conditions when the well test unit was available. In all, six WMP boreholes and three existing boreholes could be tested with the well test unit. The records of the results are shown in Volume 6A in the supplement of each of the tested boreholes.
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8
The boreholes tested were:
Existing: 3/67, 2/69, 1/77. WMP: 66/78, 106/78, 125/78, 1/79, 10/79, 42/79.
Shallow Wells. In order to establish the water potential for typical shallow aquifers in the region a series of shallow wells were selected during the inventory that were considered as representative. Well tests were carried out for the wells. The equipment used was a Honda pump but it was soon evident that the pump emptied the wells too rapidly and that the possibility to vary the pump capacity was limited. The test thus had to be carried out by measuring the recovery of the wells after the pumping. In all 33 wells were investigated in this way. The results are given in Chapter 3 of this volume.
The well log unit of type Neltronic consisted of one spontaneous potential log (SP), two resistivity logs - one belonging to the Neltronic unit and one separate lateral resistivity log, one gamma log and one temperature log. The results were collected in the field on an automatic recorder connected to the logs.
The investigation with this unit, combined with the penetration rate, gives good information to determine the borehole profiles i.e. lithology, jointzones, waterbearing zones etc. It is particularly important to have this supporting data as in the type of drilling method used the samples not always give a satisfactory data about the conditions of the bedrock. For the older boreholes the completion forms of the drilling may be without information about waterbearing zones etc.
The unit was used in 18 boreholes, 9 of which belonging to the WMP series and 9 to the existing boreholes.
Due to lack of transport the equipment could not be used to full extent. The delivery of the gamma log and the temperature log was delayed so this part of the investigations could not be carried out in all the boreholes visited. A list of the boreholes is given below in Table 6.4 with the particular investigations made in each. The results for each borehole are shown and commented upon in the borehole catalog (Volume 6A).
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I I I I I I I I I I
BOREHOLE NO.
105/78 106/78 125/78 137/78
144/78
148/78 160/78 164/78
1/79 10/79
15/79 42/79 55/79
190/78 3/67
2/69
128/73
1/77
267/76 20/60
9
TABLE 6.4
BOREHOLES LOGGED DURING THE WMP
SP RES. RES.LAT. GAMMA TEMP.
WMP X X X X
" X X X X
" X X X
" X X X X X
" X X X X>'·
" X X X X X
" X X X
" X X X
" X X X X X
" X X X X X
" X X X X X
" X X X X
" X X X X
" X X X
Existing X X X X
" X X X X
" X X X X
" X X X X
" X X X
" X X X
10
1.5 Studies of Representative Areas
1.6
In order to obtain more detailed infon11ation about the water balance intensive studies were carried out in two representative areas. Unfortunately, the period of investigations turned out to be too short for complete and satisfactory conclusions. This work was running during the entire field period but due to delays of the drilling as well as transport problem during the control program, the work was partly hindered.
The study is described in detail in Chapter 2 of this volume.
Control of Ground Water Levels
Q~~IL~!2r:~b!21~~
In connection with the inventory of existing boreholes and after the successive completion of the WMP boreholes a regular control of the ground water levels was carried out. Also here the control group faced problems due to severe transport problems, particularly during the later part of the project.
Altogether 20 existing boreholes and WMP boreholes were controlled. It should be mentioned that only those existing boreholes could be investigated that not were fitted with a pump.
Unfortunately, the control period was too short to give more than tendencies of the water level variation. The following boreholes comprise the series that could be controlled 4 months and more. Diagrams showing the variation are presented in Chapter 3.
WMP Boreho 1 e No.
66/78 67/78 68/78
105/78 106/78 124/78 125/78 137/78 144/78
Sha 11 ow We 11 s -------------
Existing Borehole No.
3/69 7/78
The same procedure was undertaken with selected shallow wells all over the region. As already mentioned 80 were controlled representing characteristic shallow aquifers. The results are summarized in Chapter 3 of this volume and the data is in Volume 38.
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DISTRICT
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REPRESENTATIVE AREAS
TABORA REGION WATER MASTER PLAN
~ :~L~~~l:~~O~~~~t:' PER SUllDBERGS v 1- 3 5-1'3'3 TAtly SWEDEN
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The program for the areas comprised:
1. Geological investigations 2. Seismic investigations 3. Resistivity investigations 4. Magnetic investigations 5. Drilling investigations.
Installing of measuring equipment: precipitation gauge, ground water gauge, and stations for measuring the soil moisture.
The control program should be carried out by collecting results from the gauges each week as well as measuring the soil moisture. The instruments were constantly guarded by a watchman living within the areas.
Tumbi Representative Area
General -------The Tumbi representative area is situated about 10 km southwest of Tabora town and 1 km east of the village Tumbi along the road Tabora-Urambo. It consists of a well defined valley striking in the direction N-S, surrounded by ridges and debouching towards the south. The level of the lowest portion of the valley is about 1,170 m and the surrounding ridges reach to 1,255-1,288 m above m.s.l.
The length of the valley is about 4.5 km from the mouth in the south and to the top of the ridges in the north. The width is 2 km between the ridges in east and west in the widest part of the valley. The drainage basin covers an area of about 7 km2.
17
FIGURE 6.6.
VIEW TOWARDS THE NORTHERN PART OF TU~1BI BASIN
i i
18
FIGURE 6.7.
GRANITE OUTCROPPING IN THE SOUTHEASTERN PART OF TU~1BI BASIN. IN THE FORE GROUND ARE TOBACCO PLANTS.
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19
Geolog~
The bedrock consists mainly of grey middlegrained granite which is outcropping in the ridges and at the eastern side of the valley. Some parts are more gneissic with increasing content of mica. Some flat outcrops are found close to the valleybottom in the northern part. The lower portions of the valley are covered by clayey-silty sediments and the overburden in the slopes consists of mainly sand-silt with some coarser material, gravel and boulders, along the outcrops on the higher levels. In the higher portions of the valley-fi 11 the ferroginous hardpan formation is found in the ground surface in scattered locations.
On the eastern slope and at a certain level within the middle part of the valley some shallow wells have been dug. The water bearing zone here is probably the silty-sandy deposits.
In the southern part of the valley a series of shallow wells occur but here they are situated close to the valley-bottom and in the transition zone between the mbuga-clay and the silty sand.
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20
FIGURE 6.8.
VIEW TOWARDS WEST AT THE SITE OF RESISTIVITY PROFILE 6-104.
. . , , .. " '{1':,
21
FIGURE 6.9.
' ... ..
VIEW TOWARDS WEST ALONG RESISTIVITY PROFILE 6-105. THIS IS THE BROADEST PArH OF THE TUI·1I3I IlASIN.
., .... .. f
-. -. " -. -. -. -. -. -, -. -:1 I,·.' ,
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~i51. 'l~ir
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22
Land Use
The main village is situated along the foothill area of the ridges on the eastern side of the valley. Scattered houses are found in the western side as well.
Cultivation takes place only in the upper portions of the valley where mainly tobaccd fields are found. Maize and cassava are the major food crops. However, from the bottom of the valley to half way up the slopes the vegetation consist of sparse bush land with scattered trees. See Figure 6.9
23
465 470
----I - -
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DRAWl NG NO-
6.10
DATE
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6-105 6-305
o 6-104 6-304
24
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DRAWING NO. 6.11 ~ Jl~~~----JS~~--~--------------~~-----r-DA-T-E----------------l ~l~~".h~ns~.n~".~,, __________________ -TS~P~E~C~.~MA~P~--l----------------
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" 25
11
TUMBI REPRESENTATIVE AREA
2.1.1 Geophysical Investigations
The investigations at Tumbi comprises the following:
Resi stivity:
Sei smics:
Magnetics:
Profiles 6-104-106, 6-112, 6-124 Soundings 6-414-416 at BH 106/78
Profiles 6-203-204
Profiles 6-304-307, 6-313, 6-332
Resistivity Profiles (Figure 6.12.)
Profile 6-104
O-poi nt UTM:
Profile direction:
Profil e 1 ength:
Resistivity probe spacing:
Additional investigations:
Locati on:
Results:
700 m
100 m
Magnetic profile 6-304 the same O-point and borehole 5-307 at 700 m
See Figure 6.10. The profile was sited crossing the valley from hillsand-laterite on the western si de over the mbuga to the hill sanplaterite on the eastern side.
The profile starts with indications on the presence of a weakness zone. The resistivity of 200 ohmm was obtained reaching a depth qf 82 m. The rest of the profile indicated shallow depths of the overburden less than 10 m. At 200 m the depth of 17 m for the overburden was obtained. The overburden consists of sandy silty layers in the lowest part 0f the profile; the resistivities vary here between 8.5-21 ohmm. Up the slope there is sand which is lateritic at the surface judging from the high values on the resi*tivities 2000-9000 ohmm. The drilling at 700 m stopped against laterite and this layer seems to continue fairly far down the slope about 300 m. It is also present at probe 1.
26 :; J~~!,.#;
m.a.S.l. 8 CD CD o CD o 00 ':': [ I I I I i ""'~I
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8000 ---!- 4200 11, 14 2100 21 <210 60 ! I i
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RESISTIVITY PROFILE 6-104 MAGNETIC PROFILE 6-304
DRAWING NO. , ~ BROKONSULT AB 336
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6,12 +----I------~-l- --1"--'- -- .. .---J I I ~ CONSULTING ENGINEERS AND ECONOMISTS
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I Profile 6-105 (Figure 6.13)
O-point UTM:
Profil e di recti on:
Profi 1 e 1 ength:
Resistivity probe spacing:
Additional investigations:
Location:
Results:
27
4673 94 423
N 1200
1300 m
100 m, 300-500 m: 50 m
Magnetic profile 6-305 (same 0-point), BH 5-401 at 600 m; 5-206A 5-301 and 5-402 at 400 m; 5-302 and 5-403 at 600 m; 5-303 and 5-404 at 800 m, 5-207, 5-304 and 5-405 at 1000 m; 5-305 and 5-406 at 1200 m and in the extension of the profile: 5-306 and 5-407 at 1350 m, 5-208 at 1500 m.
See Figure 6.10. Profile 6-105 is sited about 460 m north of the previous profile 6-104 and with the same di recti on.
The depth to sol id rock is, in general, small, 5-7 m, in the middle of the valley. However, up the slopes on both sides of the valley the depths increase sl ightly. Between 300 and 450 m there is a depression in the bedrock to a depth of about 15 m. The depression was confirmed by the drilling of 5-206 A which agreed well with the geophysical results. Another borehole 5-206 B was drilled 20 m N of the previous gave 32 m to sol id rock. Another drill ing was carried out at 1000 m where bedrock was struck 10 m bgl also in good agreement with the resistivity sounding there. According to these two drillings a thin layer of weathered bedrock exists about a meter on top of the solid rock.
None of the other drillings reached solid rock. The major part of the overburden varies between 8 and 19 ohmm. According to the drillings the material is sandy silty and very compact and hard to penetrate. At the drilling of 5-205 B quite a few samples were sampled and sieved and the grain size distribution gave a tendency towards less clay content and coarser material with increasing depth. The top soil layers are dry and silty at the lower part of the profile while the resistivities up the slopes indicate dry sand. In the highest eastern part the sand appears to be lateritic.
Profile 6-106 (Figure 6.14)
a-point UTM:
Profile direction:
Profi 1 e 1 ength:
Resistivity p"obe spacing:
Additional investigations:
Location:
Resul ts:
29
700 m
100 m
Magnetic profile 6-306 (same a-point) •
See Figure 6.10. The profile was sited across the valley 150 m north and parallel to the previous profile 6-105.
The depths to solid rock is fairly small, less than 10 m, with exception for the soundings at 100 and 300 m where 20 m were obtained. Comparing the resistivities with the previous profile the overburden is sandy-silty in middle of the valley and becomes more sandy up the slopes. The surface 1 ayers are sandy with exception for the two lower probes taken in the middle of the profile where the material is more silty. Lateritic sand with high resistivity is found at the beginning and at the end, 800 m, of the profil e.
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~ 0 200 400 600 800 1000 1125
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~ ~R-E-S-IST-I-VI-TY--PR-O-F-IL-E-6---10-6--'------~ + MAGNETIC PROFILE 6-306 , , ~
t ~ BROKONSULT AB DRAW,NG NO. ~ CONSULTING ENGINEERS AND ECONOMISTS 6.14 5 ' _ ~ PER SUNDBERGS V 1-1 C;_III'<:~ TAQ" ~.,,--- •. o sL-______________ _
Profile 6-112 (Figure 6.15)
O-point UTM:
Profile direction:
Profil e 1 ength:
Resistivity probe spacing:
Additional investigations:
Location:
Results:
31
800 m
100 m
Seismic profile 6-203. Magnetic profi 1 e 6-313.
See Figure 6-9. The profile was sited along the Tabora-Urambo road. The O-point is situated about 700 m east of Tumbi village.
The major part of the profile shows shallow thickness of the overburden, about 10 m at the O-point and at the eastern end of the profile. A slight depression to 20 m may be noted at 400-600 m. At 100-300 m weathered and fissured bedrock was indicated to great depths.
The prominent part of the overburden consists of silt and sand. The low resistivity at the eastern end of th profile indicates more clayey material. As the profile was sited on the road the topsoil layers are the roadbank mainly sandy material. The boundary between the top soil and deeper overburden equals to the ground water table which is found about 2 m below ground level.
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341
-~ 340~-339 16-313
337
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L j/ 12 , / / / If /175
32
~~---_~8 _____ FI'2 i"6 i'2 70
1960 1205 I~;o "
, ,
.1
l' 1 f\
iJ 'I /
v ~:i. ')
·~----·+i------r-----~----~------T-·
to. + 1090 336
- I I \ I I jI-----1 - -+
I I +
~~ I1 -:- 1070
400
+
I + LJ
·----~_=~I . r----I ~ , .
800
.J 1
1100m
RESISTIVITY PROFILE 6 -112 MAGNETIC PROFILE 6-313
~ BROKONSULT AB DRAWING NO.
6.15 ~, CONSULTING ENGINEERS AND ECONOMISTS
PER SUNDBERGS V 1_3 5-18363 TA-BY SWEDEN fl'o~A~T~E--~~---~
33
Resistivity Soundings: 6-414-416 (Figure 6.16)
Siting:
The soundings were carried out as a special investigation around BH 106/78 in order to gain information about the stratigraphy of the close surroundings of the borehole. The probes were sited as follows: See Figure 6.10 and Figure 6.15. Sounding No. 6-414 3 m N of BH 106/78, 6-415 50 m N of BH 106/78, 6-416 50 m S of BH 106/78. BH 5-202 and 5-203 have been extrapolated some 10 m into the profile. See Fig. 6.15.
Results:
The depths to bedrock agree well with those obtained at the drillings. Soundings 414 and 415 gave 21 m to solid rock while 416 gave 15 meters.
The overburden is generally sandy silty but there is a tendency towards less clay content and coarser material with increasing depth, compare the results from borehole. This fact explains the boundary at about 7 m, where a transition from 10 to 15 ohmm was obtained.
masl
+ 1170 J
:] + 1140 ~
I + 1130 I
I + 1120 J
I I
+ 1110 I I
::::1 + 1080 j'
.... 1070
s
8 5-203 140/78
5-106 5-204 106/78 171/78
8 15
5-202
139/78 N
8 , 15 16 = .L. ~ ~ .... ~
'c r-:' 9,5 rS' ____ Bc: :i--------r 10 r;;; .. ~ ~
00 "::i~l C,Wl 1M -: ~ V"+ 15 ;- - ~r-
15 ~C~l , c'- r,c:.WS " I ... v [-:--:- b:r-' . t::: F.-= WS _.1.;1-:''7'-_______ -"
o L--
t=-= ,.. t7i T ,.. .. ~S 4. J....
~ +V
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H
++ H
++ H H H
H ++ ++ H t+ H
H H .;. ...
" ++ H
H
H .+ q
++ ++ ++ ++
++
:: r +t ~
50 100 M
_._-_._._-----
34
RESISTIVITY SOUNDINGS 6-414-416
I3ROKONSULT AB C.O'.($UlTING ENGINEERS AND ECONOMISTS ~ DRAWING NO.
~ 1~
Profile 6-124 (Figure 6.17)
O-point UTM:
Profile di rection:
Profile length:
Resistivity probe spacing:
Additional investigations:
Location:
Results:
35
350 m
50-100 m (varying see the profile).
Seismic profile 6-204, BH 5-201 extrapolated into the profile at 30 m, BH 5-10 (106/78) at 50 m. BH 6-310 at 220 m.
See Fi gure 6.10. The profil e was sited crossing the valley outlet in the south.
The depth to bedrock is about 20-25 m at the beginning of the profile. The resistivity determined depth agrees well with those obtained at the seismic survey and at the drill ings. Towards east the depths decrease to less than 10 m. At probe 5,270 m, weak information of presence of fissured bedrock was obtained. At the drilling of BH 5-201 about a meter of weathered bedrock was drilled through before sol id rock was struck. The material is according to the grain size analysis gravelly sand.
The overburden in general is silty and sandy but parts are also coarser material. The resistivity of this material is 9-17 ohmm in the middle of the valley and becomes higher 32-64 ohmm towards east. This fact might depend on differences of conductivities of the pore water. As infiltration takes place in the hillsand on the slopes of the valley the conductivity is lower there, whole in the middle of the valley the ground water has flown for quite a long distance and accordingly been able to bring a lot of ions into solution, thus raising the conductivity. Another contributing factor is the evaporation which is higher in the lower part of the valley.
The high resistivities of the eastern slope indicate presence of laterite. This formation was struck at the drilling of BH 5-310 but is probably so thin that it does not show at the sounding at point 220 m.
m.a.s.l.
+ 1180
+ 1170
+ 1160
+ 1150
+ 1140
+ 1130
+
+
+
T
IS xl00
342
f-- 341
340
-1-339·
338
36
!{'201 BH106 ;-IR
WL
10.5
+
Iv
:~j~
/ 1I
6-332 If'
+- 035 -.-. ____ -+-_-l+_+. ____ -!~-·---··I--------I~----··--!
334
o 200
RESISTIVITY PROFILE 6 -124 MAGNETIC PROFILE 6-332
400
§ ~ BROKONSULT AB DRAWiNG NO.
6.17 ~ ~ CONSULTING ENGIN~ERS AND ECONOMISTS
ffi PER SUNOBERGS V 1-3 5-18363 TABY SWEDEN I-cD-A""TEc--------I ~L-____ ~ __________ ~ __________________________________ ~ ____________ __J
r..t I ....... lS06l
Seismic Profiles
Seismic Profile:
District:
Topographic Sheet No.
UTM of O-point:
Profile Direction:
Profile Length:
Geophone Distance:
Description:
37
6-203 (Figure 6.18)
Tabora, Village: Tumbi
118/1
4666
N 950
1050 m
5 m
The profile is situated 1 km east of the Tumbi Village and drawn parallel to the road Tabora-Urambo. The intention of the profile was to determine the possible continuation of a weakness zone found by the airphoto interpretation. This zone is running in N-S through a valley area which is debouching about 0.5 km north of the road and which has been selected as a representative area (Tumbi representative area). The terrain could be described as a flatland with hardly any noticeable depressions. The dominant soil is the silty clay.
Results:
The thickness of the overburden varies between 10 and 15 m from the O-point and to 250 and then from 750 m to the end of the profile. In the middle part the depth to the bedrock is about constant 20 m. However a depression of 35 m is found at 5.25 m. The seismics recorded two velocity layers. The upper layer with velocities 450-700 m/s consists of dry silt and sand and the lower layer with velocities 1350/2000 m/s is estimated to be sand and gravel below the ground water level. The bedrock expoes the velocity 5000 m/s which is common for granitic bedrock. This velocity is dominating in the wide depression in the middle part of the profile, 250-750 m. On the both sides of the depression several low velocity zones are found indicating possible weakness zones, see table below.
38
TABLE 6. 5. VELOCITY ESTIMATES PROFILE 6-203
0; stance m from O-po; nt
35- 40 90-110
130-135 170-180 190-200 230-240 260-270 320-325 325-350 350-425 790-795 885-890 935-940
Velocity m/s
1700 4000 3400 2700 3000 3000 2200 3000 3600 4000 3000 2300 2900
A--
----r 5000 m!s
~Iill
T 7, -.... -<
i---
mamsl -'-1160
+1150
-+1140
~1130
500m
,{, '\
-1-----
~ ! -,
__________ -SOoom!s __________-1
1000m
mamsl ... 1160
... 1150
+1140
+1130
. "---.--~'--".'--.----------.,-. --~----------
39
465 -1"<, ..
/'.'-." -... ...... ..:-. 1 C .... 'v·... ! \.,.....' t i , 1
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',.(-'
. /-\ ;-----._. . .,
\ ( \.-.....
~.\
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f""1_./·-.....·-J
TABORA REGION
The United Reoublic of Tanzania Hinistry of \~ater Developll1ent, Ener9Y and t,1i nera 1 s
I "/ I VP;~'>~1944
Tumbi , .,:
6-203 ,,~., _=1 ~ )6_313;""
1160 ;;_
---_ .... ; ... ;; :: - -=- --
PART OF TOPOGRAPHIC MAP SHEET No 116/1 1 :50000
International Bank for P-econstruction and development
TABORA REGION WATER MASTER PLAN
SEISMIC SURVEY: PROFILE 203
~ BROKONSULT AB ~ CONSULTING ENGINEERS AND ECONOMISTS
ORAWINGNO. 6_18
PER SUNDBERGS V. 1_ 3 S~18363 TA8Y SWEDEN OATE.
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40
Sei smi c Profil e: 6-204 (Figure 6.19)
Di stri ct: Tabora, Village: Tumbi
Topographic Sheet No.
UTM of O-poi nt:
Profile Direction:
Profil e Length:
Geophone Distance:
Description:
98/31
4673
N 950
550 m
5 m
The profile is situated in the suthern part i.e. close to the orifice of the valley that was selected as a representative area, the Tumbi area. The profile crosses the lower portion of the valley and in the middle part the overburden consists of silty clay and on the si des of si 1 t and sandy si 1 t. On the eastern si de of the profile there is a zone of shallow wells which are said to be waterbearing during the whole year.
Results:
From O-point to 80 m the depth to the bedrock is 20-30 m and from 320 to 550 m the depth is 15 to 25 m. In the middle part of the profile, 80 to 320 m the depth is decreasing to 5-15 m.
The overburden has two layers, the first layer of which has velocities of 400-600 m!s indicating dry sandy - clayey soil to depths varying between 6-10 m. The second layer with velocities of 1300 to 1600 m!s consists of sand and gravelly sand below ground water level.
The dominating velocity of the bedrock characteristic for granite or gneissic low velocities are found (see table). the depression in the beginning of the
TABLE 6.6.
is 5000 m!s which is granite. Several zones of One of them is located in profile, 3000 m!s at 55-70 m.
VELOCITY ESTIMATES PROFILE 6-204
Di stance m from O-point
55- 70 320-340 460-470 490-495
Velocity m/s
3000 3000 3200 2000
Remarks
BH 106/78 located at 60 m
41
A borehole 106/78 was sited on this low velocity zone and the results correspond generally rather well with the interpretation of the lithology of the seismic profile.
However in the drilling point there are some differences. The bedrock was struck about 8 m higher than suggested which is explicable to the fact that the low velocity zone corresponded to a possible fault as well as to a rather deep transition zone between the weathered, decomposed granite and the fresh granite. The ground waterbearing layer was struck in the hole at the surface of the bedrock. The ground water level was here 8 m lower than estimated in the seismic profile.
"o"",~Jjt!';F- .,,.fiM .t, A"A;t21g;%~;">,;::,,,.:.~ .. ,> -,---------. -~. ~~~~=======r,~
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470 r----~,.C-__'-;T,CnC<c=-7/-,.--T",__C,C,C,T,,,,_:_lj
;::;:£11 = = -= JJI .:::: r =("~-=~ -mamsl
+1170
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_i-----!.AS~ I . \. __", . 'I
'-'r'> -- "-1--/-, -------.?, ~ \ ! - \
"....... j .. \ ,/ . / I ./ . \
~1_ ............. ..;
TABORA RE ION
The United Reoublic ( ~1inistry of Hater De' Energy and Minerals
Tanzania lopment,
PART OF TOPOGRAPHIC MAP SHEET No 118/1 1 :50000
International Bank fOr P..econstruction and development
Tt BORA REGION WAT :R MASTER PLAN
SEISMIC SL ~VEY: PROFILE 204
DRAWING NO 6.19 ~ BROKO SULT AB ~ CONSUL TlNG ENGI ,RS AND ECONOMISTS
S-1 ;3 TA BY SwEDEN PER Sl!~108ERG5 v 1- J
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Magnetic Profiles
Magnetic Profile:
Location and Siting:
Results:
43
6-304(Figure 6.12)
The profile was carried out in compliance with resistivity profile 6-104. It has the same O-point and ends 230 m east of the last probe 8. See fig. 6.11.
The values increase from normal at the O-point to a maximum of about 34650 gammas at 220 m. After the peak the values drop rapidly to 33600 at 300 m and continues towards W undulating about 33700 gammas.
The anomaly was obtained close to where an increase in the depth to bedrock was indicated by the resistivity investigation.
Magnetic Profile:
Location and Siting:
Resul ts:
6-305 (Figure 6.13)
The profile starts at the O-point of the resistivity profile 6-105 and ends at BH 5-208. The total length is consequently 1,500 m.
A very prominent anomaly was obtained at about 400 m which shows great similarities with the one in the previous profile. The peak value in this case is higher, 34940 gammas and the anomaly was registered in immediate vicinity of a depression in the bedrock.
Magnetic Profile:
Location and Siting:
Results:
6-306 (Figure 6.14)
The profile runs in compliance with resistivity profile 6-106. It ends 225 m east of the last probe 10.
An anomaly of the same shape as in previous profiles was achieved between 200 and 400 m. The peak value reaches 34700 gammas. As in previous profiles a slight depression in the bedrock was indicated at the place of the anomaly.
44
Magnetic Profile:
O-point UTM:
. Profile Direction:
Siting and Location:
Resul ts:
6-307 4 678
N 10°
(Figure 6.20) 94
406
The profile was sited along the path following the valley direction to search for tectonic irregularities traversing the valley. The profile crosses profile 6-104/6-304 at about 750 m. See location map 6.11.
No significant anomaly was obtained. The values are varying about 33650 gammas.
, ~rt/ ~~,,-.
,." 1"
~, ~:;
-It
---. " -t, ~I ~' •. i!.~;.
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I) T, ,{
x 100
.340
339
.338
337
.336
• 340
339
+ 338
337
+ 336
+
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+
~
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" ~ ~ 0 ~
'" ~ ~ ~ ~ ;;:
1= w
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45
,--------~- -,---- -- .---.----r---~T
~ ~ ~ ~
2 0 4 0 6 0
--
I i
--.~--
"\ V \ LA-LJ I -,..-_._.
8 0 10 00 llpOm
I
-J . ----f----- t-....... - j-- ----- ----
I i -I I , j--+- I !
- I --L--_
I I ,
. 1---_ .. _----- j ~------. __ ._----.---... ~
.~-.--I .. _-" ... - -_ .. --_ .. __ .-
I I I I
I -t-~--l-~--- -- f------ --, i I
J ____ _ __ ---I- ---- ---_.- ------_ ..
MAGNETIC PROFILE 6-307
~ BROKONSULT AB DRAWING NO. 6.20 CONSULTING ENGINEERS AND ECONOMISTS
PER SUNDBERGS V. 1- 3 5-18363 TABY SWEDEN DATE
Magnetic Profile:
Siting and Location.
Results:
46
6-313 (Figure 6.15)
The profile starts 100 m W of resistivity profile 6-112 and ends 200 m E of it following the Tabora-Urambo Road. See fi g. 6. 1 O.
Slightly higher values were obtained at 0-400 m of the resistivity profile where indications of weathering to large depths were achieved. There seems to be a relationship between the presence of the weakness zone and this weak anomaly. Another stronger anomaly was obtained between 500 m and 700 m which shows the same shape and fits to the positions of those obtained at the previous magnetic profiles. There is also a slight depression in the bedrock at the position of this anomaly similar to previous cases.
Magnetic Profile:
Siting and Location.
Results:
6-332 (Figure 6.17)
The profile is 610 m long and starts 100 m W of the resistivity profile 6-112. It ends 160 m up the slope E of BH 5-209. See fig. 6.11.
The profile starts with an anomaly similar to those in previous profiles. The peak value reaches 34300 gammas and the lowest value is 33300 gammas. The anomaly was obtained between 50 and 150 m and fits well to the presence of a depression and a weakness zone obtained at the seismic investigation. However, at the drill ing of BH 106/78 no tectonic zone was struck.
47
Summary of Geophysical Investigations
The bedrock surface in Tumbi valley seems in general to be very fl at. The overburden thi ckness is about 10 m in the mi ddl e of the valley and increases up the slopes on both sides to the outcrops. A slight depression was discovered in the western part of the va 11 ey. It runs in northsoutherly di recti on and is about 100 m wide. It reaches about 15 m below ground level in the north and about 20 m in the south. The·depression appears in connection with a prominent magnetic signature which easily can be followed from one profile to another on the ground magnetic surveys. The later review of the airborne magnetics showed that this anomaly fits into the general N-S magnetic pattern which covers most of the region. No intrusive rock or weakness zone has been indicated at the drillings; an eventual dyke is situated further to the west or the anomaly is caused by a more magnetite-rich part of the gneiss which obviously has weathered to somewhat larger depths when compared to the surrounding bedrock.
The overburden is silty sandy and very compact. There is a tendency towards less clay content and slight coarser material with increasing depth. The solid rock surface is covered by a layer of weathered bedrock of a thickness of about one meter. The major part of the ground water flow is presumably taking place in this layer.
The topsoil layers are silty clayey in the middle of the valley thus allowing almost no infiltraion during precipitation occasions. Up the slopes the topsoils are sandy silty and quite permeable. However, here is also found a layer of laterite which in some parts of the valley is rather impervious and makes the percolating water return to the ground surface down the slope and run off as sheet flow. The major refill of the deeper strata in the valley takes place through infiltration close to and in the fissured exposed bedrock.
2.1.2
48
TUMBI - DRILLING
Introduction
As already commented in the description of the geophysical investigations a number of boreholes were drilled: One deep borehole 5-206 (106/78) with the Schramm rig in the bottleneck of the valley. 10 shallow boreholes 5-201-206A, B - 209 with the CME rig and finally 2" ground water observation pipes 5-301-310 and 2" soil moi sture observati on pipes 5-401-412.
The boreholes served three purposes:
a. Control and complete the picture of the lithology surveyed by the geophysical investigations.
b. Control of the ground water conditions.
c. Supply the soil moisture investigation with suitable observation pipes.
General
On the whole the drilling results coincide well with the results of the geophysical investigations. The drillings have confirmed the presence of the structure running along the western side of the valley from north to south. According to the deep borehole at the outlet of the valley the structure does not imply any weakness zone nor any dyke but depends on a local more magnetite rich part of the gneiss.
The depths to bedrock increase from some 10 m in the central part of valley to about 20 m in the outlet of the valley. A slight relative increase in depth can be followed along the structure.
The many dri 11 i ngs wi th samp 1 i ng and soil investi gati on have given a good picture of the composition of the overburden.
49
The dri11ings are commented and listed as they appear in the geophysical profiles. The positions of the boreho1es are given in fig. 6.11.and the records of the dri11ings are shown in their respectiveprofi1e. If any additional investigation has been carried out as soil analysis, study of the penetration rate etc, boreho1e record has been given separately in this section.
Results
Profile 6-104
Only one borehole as carried out in profile 6-104:
Boreho1e No. Distance Depth
5-307 700 m 3.5 m
The borehole was drilled in the vicinity of outcropping laterite in order to maintain a record of the ground water level in the sediments on top of the impervious laterite. The latter was struck at 3.5 m and the static water level was recorded 2 m.b.g.l. in December, 1978. The drilling penetrated sand from the ground surface to the bottom of the hole.
50
Profil e 6-105
The following boreholes were drilled in profile 6-105:
Borehole No. Distance Depth
5-401 200 m 4.0 m
5-402
5-301
5-206 ) 5-206B)
5-302
5-403
5-303
5-404
5-207 ( 184/78)
5-304
5-405
5-305
5-406
5-407
5-208 (285/78)
400 m
400 m
400 m 400 m
600 m
660 m
880 m
800 m
1000 m
1000 m
1000 m
1200 m
1200 m
1350 m
1500 m
3.5 m
3.5 m
14.5 m 32.0 m
5.0 m
5.0 m
2.5 m
2.5 m
11.0 m
3.0 m
2.5 m
9.0 m
4.5 m
2.5 m
17.5 m
Remarks
No contact with solid rock formation too hard.
" "
11 11
10 m N of 5-206A - See attached borehole records with soil analysis. Fig. 6.21.
No contact with solid rock formation too hard.
" "
"
" "
No contact with sol id rock formation.
No contact with solid rock formation too hard.
" "
The determinations of the bedrock position coincide well with the resistivity at 400 and 1000 m where the CME drillings reached sol id rock. It should be mentioned though, that the drilling 10 m N of 400 m 5-206B reached 32 m so the depression recognized at 350-400 m is obviously deeper towards N.
... 1167.8
BH 183/78A (5 -205Al
+ 11670 Of, Soil analysis +_+1 VL ·100
0
T1-------__
:;;:a= 12
2
3
4
5
6
7
8
9 -j 0 0
o 0
10 -I o 0
o 0
11 -I . o 0
12~
52 50 sand
12 36 o clayey silt
0,001 0,01 0.1 10mm
% Soil analysis
100
48 SO sand
12 40 clayey silty 0 0------;
0.001 0.Q1 0.1
Soil analysis %
1 10mm
100
i ! SO
o I , ~ 40 5~ sandy ?rovel
0,001 0.01 0.1 1 10mm
13
14
15
16
17
18
19
20
21
22H
23i l-24
51
% Soil analysis
100 -':7"'1 24
50L/ ! Lw
0' ~ i , sand 25
0,001 0,01 0.1 lDmm
26 " o 0
o 0
27 ~ o 0
% Soil analysis
100 I i 501 £. I
o L_~_.3/:,"~d I 0.001 0.01 0,1 1 lDmm
o 0
28 H .. o 0
29 ~ 0 0
o 0
o 0
30 o 0
o 0
31 l' o 0
.0 0
32
% Soil analysis
100 r----.. ----.. SO c
o~ sond6O
0,001 0,01 0'1-·-·-....---·-----1 . 1 10mm
DRAWING NO. 5.21
DATE
;",~'-i"
52
FIGURE 6.22.
AUGERING WITH THE BORRDS DRILLING MACHINEAT 200 M IN PROFILE 6-105 (BH 5-401)
The major part of the ovet'burden consists of sand and silt which is very compact and ilard making it almost intpossii)le to penetrate by percussion and is further indicaterl'ly the difficulty to dri 11 th rou0h the lJyer wi th the 1 i ght BOt'ros dri 11 i ng machine. The hard formation combined with a noderate clay content of the top soil s makes the overburden in the central p'art of the profile almost impervious. This condition might explain why no ground water was struck during the drillings in the profile. However, at the drilling of 5-2068 north of the profile water \Vas struck at 26 m which rose to 24.5 m b.g.1- indicating that the ground water taill e at the time of the dri 11 ing (end of dry season) was situated 10lver than the position of the solid rock in profile 6-105.
53
FIGURE 6.23.
PULLING UP THE RODS. AlIGERING AT 200 M, IlH 5-401 IN PROFILE 6-105
,-,-om ahout 1100 m and fUl-ther towards SE the top soi 1 layers change to more sandy material. The drill ings at 1200 m discovered more sandy material which occasionally is lateritic. The drilling at 1300 m probably stopped at lateritic hardpan. This fonnation seems to o(J;ur occasionally as part of the strata of the hill sand area even if it cannot he seen outcropping on the surfaceat the site of the profile.
Drilling 5-208 was carried out not too far from outcropping rock and penetrated sandy and sil ty layers \1ith no indications of hardpan lateritic formation.
54
Profil e 6-124
Several boreholes were drilled in the profile and in the vicinity of deep BH 5-106 (106/78).
Borehole No. Distance Depth
5-106 60 m 98.8 m (106/78 )
5-201 20 m 22.3 m (238/78 )
5-202 20 m 19.8m (139/78)
5-203 20 m 22.9 m (140/78 )
5-204 10 m 22.3 (179/78)
5-205 ( 180/78)
5-209 (186/78)
5-308
5-309
5-310 5-311 5-312 5.313
20 m
330 m
o m
160 m
210 m 220 m 220 m 220 m
19.2 m
14.6 m
3.0 m
3.0 m
3.4 m) 3.0 m) 3.2 m) 3.0 m)
Remarks
See attached BH description extracted from Volume 6A.
SW 5-106 See attached BH record with soil analysis.
N 5-106
SE 5-106
N 5-106
NE 5-106
See attached BH record with soil analysis.
No contact with sol id rock.
.. ..
At the shallow well
55
The determinations of the depths to bedrock coincide well with the geophysical investigations. The thickness of the overburden decreases from about 20 m determined at and around BH 5-106 (106/78) to about 15 m at the eastern end of the profile BH 5-209 (186/78).
The overburden consists mainly of sand and silt. are clayey in the lower part of the profile while be more silty on the slope. The thickness of the layer is according to the drill ings in the center valley about 1.5 m.
FIGURE 6. 23B.
The top soil s they appear to cl ayey topsoil part of the
PERCUSSION DRILLING AND SAMPLING AT BH 5-310 PROFILE 6-124
BH 5-310 Q!
a. .. .. a. E
d E"'
EU 0
E't mbgl
o .11677 0 f1 (/)
.cc .c::> 00 oU)
I
y 1 150
~ 2 t<-
o 0 2
46.2
t 15.6
3. 11.4 12
0 0
~ J 3 1
% Soil analysis.
100 1.
50
26 51 clayey sand
0 0.001 0.01 0.1 1
100 2.
50
20 60
0 clayey sand
~~-r , 0.001 0.01 0.1
100 ~----------13.
50 I 19 52
o clayey sand ~ ... ------,----.-----,-'-'~"'~
0.001 0.01 0.1 1
56
Penetration rate
15 30 45 bumps / 20cm o hr ___ i-___ -L_~
100/20 cm
10 mm
10mm
10mm
DRAWING NO. 6.24
DATE
57
The shallow drilling at 210 m, 5-310, was carried out in the transition zone between the valley bottom and the slope. As shown in the Figure 6.24 the upper 3 m were easily penetrated consisting of clayey sand. The soil was saturated with water obviously trapped by impervious laterite which was struck at 3.20 m b.g.l. A few seasonal shallow wells are dug in this section of the valley, one of which is situated close to the profile.
.' ;',
~ " .
tt ~~I
t I I j
I I
·'1 "~
; .......• .. , .... '?
;~'I·. " li:,
58
FIGURE 6.25
RIG 53 DRILLING BH 5-201 IN TUMBI BASIN
The major part of the overburden is silty sand with a tendency towards coarser material at larger depth. Soil analysis of the bottom-most material from SII 5-201 (138/78) showed sand and gravelly sand. These layers are obvious \'iaterbearing as ground water was struck there at most of the drilling operations in the central part of the valley. The ground water rose to about 14 m b.g.!. in the drill holes at the central part of the valley. The drilling and soil analysis of BH 5-209 (186/78) showed more than 70% sand down to a depth of 12 m when the clay content increased to about 20%. Ground water was struck at 10.7 and 4.5 m b.g.l. and rose to about 2 m b.g.l.
+ 1166,8 ", __ .:L
·59 I
BH138178 (5-201)
mbgl o
1
3--1---1
4-·1--1
+ 1166,1 v
12 ~-~
00
00
13 o 0
14
15
16
% Soil analysis_
100
50
o 100
50-
70 sand
22 50 o -- wavell~_ . ..:s:.:a:c.nC:;~'--__ -i
0,001 0,01 0.1 1 10 mm
DRAWl N G NO. 6,26
DATE
'.! "
61
The detailed information on BH 106/78 is repeated here from Volume 6A for completeness.
1. Borehol e No.
2. Siting:
3. Location:
4. UTM:
5. Levels:
6. Drilling details:
106/78, WMP No. 5-106
The Tumbi representative area is situated about 10 km WSW of Tabora and 1 km E of the Tumbi village along the Urambo road. See map 106/78:1 (topographic sheet 118/1).
Air photo showed a well defined valley striking in N-W surrounded by ridges and outcropping bedrock and debouching towards the south. The valley bottom is covered by mbugasilt and the slopes mainly by sand-silt. The bedrock consists of granite. DUring the field survey several outcrops were found at the eastern side of the valley and also close to the valley bottom. Some water holes were found on the gentle slope close the valley bottom.
The following geophysical investigations have been carried out within the representative area, one seismic profile 6-204, three resistivity profiles 6-104, 6-105 and 6-106 and four magnetic profiles.
The results of the geophysi cal survey show a weakness zone depression running in southnortherly direction along the western side of the valley bottom. Furthermore, the magnetic survey showed an anomaly coinciding with the depression.
Tumbi, Ilolangulu Division, Tabora'District. Seismic profile: 6-204 60 m east O-point.
94402 Ground level: Top casing:
Depth: Water struck: Water 1 evel : Ca sing p 1 a in: Casing slotted: Uncased:
1166.31 1167.06
98.8 m 21.0 m 15.4 m 0.0-20.6; 25.5-31. 5 m 20.6-25.6 m 31.5-98.8 m
7. Water levels:
Description of profil e:
m 0.0- 2.7
2.7- 4.3
4.3- 5.8
5.8- 8.8
8.8-20.0
20.0-21.0
21.0-22.6
22.6-29.6
29.6-34.2
34.2-52.4
52.4-54.0
54.0-58.8
Yield and
62
Control date m below top casing
09/08/78 14.0 18/09/78 13.09 13/10/78 13.10 04/11/78 18.60 14/11/78 13.30 23/11/78 13.94 28/12/78 13.25 19/01/79 13.21
Recorder installed 19/01/79.
See 106/78:2
Greyi sh cl ay.
Greyish sandy clay.
Browni sh sandy si 1 t.
Greyish clayey silt.
Greyish silty sandy gravel probably boulder of weathered granite.
Greyish silty sandy gravel (weathered).
Brownish weathered granite, clayey.
Greyish weathered granite, sandy.
Brownish weathered granite.
Greyish fresh granite.
Brownish granite.
Greyish granite partly coarse grained. 3
Yield: 1.1 m /hr tested by airlift 8 hrs.
Well test Aqui fer test 24 hours. See 106/78:3:1_4 3 Safe Q = 1.4xlO m/sec.
T = 2. Oxl(J6 m 2/sec • S = 2.8xlO
10. Geophysical profil es:
11. Well log: See 106/78: 2
12. Water Analysis:
13. Remarks:
63
Seismic: Resi sti vity: Magnetic:
6-204 6-104, 105, 106 6-304, 305, 306, 307
Comments: The penetration is fast down to bedrock surface. The low speed through the weathered portion of the bedrock down to about +1120 (35 m) probably depends upon that the drill bit had not been changed. Below +1128 m the penetration diagram indicates the use of two compressors and the variation of the rate shows that the bedrock is intersected by small joints.
Below the waterstruck zone with the casing the resistivity curves are gently undulating down to +1082-83m "hdicating finely jointed bedrock with possibly small seepage zones. Below this level the bedrock is dense.
Tho temperature is ranging between 270C and 30 C.
See 106/78:4
-.. t}
(') :'?
n ".,
m.Q,sJ
... 1170
... 1160
... 1150
.. 1140
.. : 1130
+ 1120
... 1110
... 1100
.. 1090
... 1080
+ 1070
BH 106178 (5-106)
PENETRATION RATE {mini
o 20 40 60 , I Te ·"67.6 _ 4- .. ~I GL ""11563
!
~·r I +-- I + V > ::~ li
£ .. ?£.o ~
I +V+ - ~ I +V~ ~
+--++v: I~ I tV+ - + + +
:: -~~ ..... I i : : I, I I : : --I + . . + ~ '-----j
1 + + I ! +----i ... + i
+ + i i: + ... i _+-. ----, . , 1++ - , I
T---i I + +
+ +
""--'I~ ~ -'-- I I t I, +-:: -, I I
+ +
~"'-'"''
SP{mvl
o 100 200 , I I '
'~_.]I __ ~ ! :-1
I '
i ! :
. I LI -c-
I;IJ
RESISTIVITY {k ohmml R.LATERAL {k ohmml TEMP {C'I
o 2 4 0 2 3 4 15 20 2S
~H J
I l , I
f-----''-----+--+-~' I
f---+---+--~!~ I I:
I I I I I ,
11 I i !, 1\ i--(
I---i-+--- r)l __ -1
I
\1 i I
f---4 !--: I d
I
,
I
u- , H-
I i i
I ---T---'--
I -t t,
r-~'
BOREHOLE 106178 WITH WELL LOG
(-~ C~O~<ONSULT AS i ORAWING NO.
'-- ) / CC:'SULTING EN(,iNE;::;<S ANO ECONOMISTS 6,28 =-PER S:J~1D8SRGS v 1-3 5-18363 Tliay SWEDEN ~
65 106/78
EGION: Tabora LOCATION: Tumbi
ISTRICT: Tabora BOREHOLE NO: 106/78 (WMP) ........................
---------------------------
ate ~~---------------------------------
r----------------~--------
.t:..~_ductivity m S/m 240
.:D!.Cbidity 20
Colour Nil
pH 7.8 ---------------------------
Tota 1 Hardness meqv 11 12.0 -------------------- ----
Calcium (Ca) mg/1 164 -------------------------------- ---
~~a..g..ne~!um _(liV mg ~ ____________ 4_6 ._6 __________________________ _
A 1 ka l.Lfjity meqv /1 _ 2.28 -------------Sulphate (504) mg/1 12 ----------------------------- ----------------
I-,-on_(F_eJ mg/l 0.07 ---- ---------- ------------ --- -- - -------------------
Nil ---- ---------------------------------
0.03 Fluoride (F) mg/l
Al1moni~_lN1.mg/l
-----------------------------------
0.5
Pel-manganate Value mg/l 5.0 ---------------------- ----
22.25
66 106/78:3
AQUIFER TEST RH 106/78 TUMBI 17-18/11/79
Time after DRAWDOl,N IN m Recovery pump start testho1e Rema rks
Min. Sw
0 0.00 0.00 0.00 0.00 0.00 29.67 1 1. 47 0.04 0.01 0.02 0.04 28.37 No recovery 2 1. 40 27.29 measurements 3 1. 42 26.44 from obse r-4 1. 44 25.57 vati on boreho1es 5 1. 46 24.76 6 1. 50 23.64 7 1. 52 23.32 r ~ 20 m 8 1. 55 22.78 3 9 1. 59 22.18 Q ~ 0.7 m /hr ,
10 1. 62 0.02 0.04 0.29 0.07 21. 57 1.9xlO-4
12 1. 68 20.30 Average va 1 ue 14 1. 74 18.93 16 1. 79 17.70 18 1. 82 16.64 20 1. 85 0.06 0.04 0.00 0.01 15.40 25 1. 92 13.00 The drawdown in· 30 1. 97 0.02 0.04 +0.01 0.01 12.23 creased rapi dly 35 2.02 12.10 around 28 m BTC 40 2.07 0.02 0.04 +0.01 0.01 12.06 whi ch mus t be 50 2.18 0.02 +0.01 +0.03 0.00 11.78 taken into con-60 2.23 0.02 +0.01 +0.02 0.00 11.27 sideration if
70 2.27 0.02 +0.01 +0.02 0.00 10.26 installing a
90 2.46 0.01 0.01 +0.02 0.01 9.36 pump 120 2.75 0.02 +0.01 +0.01 0.01 7.73 Two shorttime 150 3.01 0.01 0.00 +0.04 0.01 6.45 tests (4 and 5hr)
180 3.19 0.01 +0.03 +0.04 0.02 5.48 showed the same
240 3.84 0.01 +0.03 +0.04 0.02 res ult as the
300 4.41 0.04 +0.03 0.04 0.01 24h rs. 360 5.07 370 0.04 +0.04 0.07 +0.01 480 7.59 490 0.09 +0.03 0.15 +0.01 600 9.31 610 0.18 ,·0.01 0.25 0.03 720 10.82 730 0.23 0.01 0.33 0.01 840 11. 68 850 0.30 0.01 0.42 0.01 960 11.96 970 0.36 0.03 0.51 0.01
1080 13.21 1090 0.43 0.05 0.59 0.04 1200 16. 13 0.75 1210 0.53 0.13 0.67 0.05 1320 23.21 1330 0.54 0.11 0.72 0.04 1440 29.67 Pumpstop!
1450 0.62 0.14 0.82 0.05
67
Comments on the Well-Testing Result of BH 5-106 (106/78)
The well testing of BH 106/78 was carried out as an aquifer test with observations on the drawdown during the pumping in the surrounding BH:s 5-201 (138/78), 5-202 (139/78), 5-203 (140/78) and 5-204 (140/78B). However, very little or no reaction was observed in the two northern boreholes 5-202 and 5-204, see Table 6.6. This might depend on the fact that those holes were either poorly flushed after the completion or that they were drilled to another aquifer. However, nothing in the geophysical investigations pointed towards the presence of any aquifer not connected to the one in the vicinity of BH 106/78.
The aquifer test was performed at a constant yield of 0.7 m3/h The pumping continued for 24 hours and observations were carried out regularly during this time. After pump stopped the recovery was measured in the tested borehole. All data from the pumping test is collected in 106/78:3. The time drawdown curve from the well test shows a discontinuous behavior indicating that the aquifer is i nhomogeni ous and evi dently consi sts of "pockets" which are gradually emptied during the testing. Moreover, the rapid drawdown at the end of the test indicates that the yield was chosen to be too high. But, by modifying the drawdown values according to the formula:
where:
h m
~ ho
= h 2 (ho -h)
2 ho
= The modified drawdown value = The actual drawdown value = The initial static water level
A fairly continuous curve was obtained for at least the middle most important part of the curve allowing T to be determined.
Thus, the presumption of homogenity and isotropy cannot be considered fulfilled and hence the T value calculated may not be rel iable.
However, the recovery data show a fairly continuous curve when plotted and the storage coefficient and transmissivity calculations from the drawdown in the observation holes also contribute to the calculation of an average T value for the aquifer at the Tumbi valley outlet. The table below gives the calculated permeability from the lithology at BH 106/78 consisting of the following layers:
68
Aguifer Layer Thickness Estimated Permeability
Si 1 ty sand 5 m -6 10 m/s
Gravel 1 m -4 10 m/s
Weathered grani te 13 m -6 10 m/s
Total aqui fer 19 m -6 6.2 x 10 m/s
In the following table all values concerning the aquifer are collected. Furthermore, the yields corresponding to each permeability is calculated according to the formula used to relate recharge, yield and subsurface conditions, see Chapter 3 of this volume.
Litho. Ca lcul. Aqui f. Test Modif. Recovery Observ.Pipes See above Drawdown 106/78 Date 106/78 5-201 5-203
Storage Coeff. S 3 - -6 --6 0.0049_50.0033_5 Transmis.T(m Is) m - -6 4.24x10_7 2.7x10_ 7 3.4x10_62.3x10_6 Permeability(m/s) 6.2x10 2.23x10 1. 4xlO 1. 8x10 1. 2xlO Q (m /h) m3 2.7 0.12 0.08 0.82 0.61
The table tells that the estimated permeabilities from the lithology are too high when comparing with the values obtained at the welltesting. The values obtained at calculations from BH 106/78 data are in general low when comparing those obtained from the observation pipes. The low and discontinuous values due probably to the following:
1. The horizontal distribution of the aquifer is limited. No drawdo~m was measured in the observation pipes north of BH 106/78.
2. There is a vertical distribution of aquiferous layers with different hydraulic properties. The time-drawdown curve at the yiel d test presents several "steps".
'H
'..'-: .-,'
69
Soil Moisture Measurements
The measurement methodology is penetratingly described in Volume 4, Chapter 5. In the following only the results from the Tumbi basin as an isolated water balance system will be discussed.
The Measuring Program in Tumbi Basin
Altogether 12 stations for soil moisture measurement were installed in Tumbi representative area. Every station with one exception (5-401), consisted of two tubes one plain tight for the soil moisture measurement and one with perforated point for ground water level observations. The latter was generally set to about the same depth as the former.
The stations were measured about once a week from the end of 1978 to May 1979. At each station a reading was taken each 0.1 m at the top of each tube and thereafter every 0.2 m to the bottom of the tube. See the picture. At the same time the ground water level was taken in the nearby observation pipe.
Resul ts
As already pointed out in Volume 4 the observation time is far too short for any definitive conclusions to be drawn. But the following trends can be noted: When comparing the moisture content of the soil s at the center of the valley with those * achieved from the observation pipes drilled in the hillsand it can be notified that the moisture content is generally higher at the center of the valley. This difference is larger during periods of little or no rainfall emphasizing the presence of more fine grained and more water keeping-material at the center of the valley.
At the slopes where the more coarse grained material prevails the water percolates faster tL·JS showing a less moist content., The content also tends to be more seasonal dependent as low values were obtained during periods of extensive draught. Thus the soil moisture measurements confirm the theory of very little infiltration in center of the valley while the main recharge of the ground water takes place in the hill sand areas up the slopes.
* See appendix 5, Volume 4.
70
..
"',
.. '~-'<",;' ," , "f" ,.-
FIGURE 6. 29
SOIL MOISTURE MEASUREMENT AT 5-404 TUMBI BASIN. NOTE THE GROUND WATER OBSERVATION PIPE 6-303 CLOSE BY.
2.1 .3
71
Summary of the Ground Water Conditions in Tumbi Representative Area
The occurence of the ground water in Tumbi area can be separated into two major aquifers.
One shallow aquifer supplied by water recharging in the hillsand area and within the exposed 'bedrock area inside the water divide, see Fi gure 6.30. The permeabilit~ of t~e materi al in the shallow aquifer is fairly high 10- - 10- m/s estimated from the grain sizes. The ground water level varies from one spot to another depending 0 the occasional occurence of laterite blankets which are buried in the hillsand. Hence there was no laterite and no water struck at the drilling of 5-208, while 5-305 ended on laterite. This last borehole responds comparatively fast to precipitation and shows fairly large variation, see Figure 6.31 The laterite blankets are more or less impervious and trap percolating water allowing part of it to continue downwards and forcing most water via subsurface outflow to the ground surface at the lower portions of the slopes. This water forms a sheet flow on the ground surface and is collected at the bottom of the valley where it evaporates.
The deep aquifer occupies the central part of the valley. It is mainly refilled by water from the shallow aquifer which flows through the coarse porti on of the overburden close to the surface of the bedrock. The communication between the two aquifers is very poor; a fact which is shown by the large differences in the positions of the static water levels, e.g. at BH 5-209 the level is 2 m b.g.l. vs BH 5-106 where the water level is about 15 m b.g.l. Also taking the difference is ground level between the two boreho1es into consideration the total difference in static water 1 evel sums up to about 20 m in a di stance of 300 m. .
A very small contribution to the aquifer is achieved from precipitation and sheet flow (see above) on the soils covering the central parts of the valley. The drillings have shown, that the soils are very fine grained and compact but the soil moisture measurements have proved that small amounts of water do, in spite of this fact, percolate through the overburden.
The upper parts of the valley appears to be dry most of the year with exception for occasional deeper depressions e.g. at BH 5-206B where ground water was struck 25 m b.g.l. (+1145 m). At the valley outlet in the south the level was recorded 16 m b.g.1. (+1154) at the same time. The differences in level is either another proof of the poor communication within the deep aquifer or means that it is separated into two basins by a threshold of bedrock.
~.'" :' 1('
I'
,;,
72
Figure 6.32 shows the ground water variations during one year in BH 5-106. The variation is, as might be read from the diagram, very small and no reactions are achieved from the ground water level on occasions of precipitation. The low value in the later part of November is suspected to be a measurement error.
At the bottom of the diagram the levels from 13 days in February 1978 can be studied in detail. The cm-fluctuations obtained depends probably on the tide.
LAGE'RBI..ANKETT FJLM PT 15 FORMAT A4
i Fig. 6.30 SIMPLIFIED PICTURE SHOWING THE GROUND-WATER CONDITIONS IN THE UPPER PART OF TUMBI VALLEY WATER
Dl~ +1220-!-
~ -t
+1200 I I
i~ ~ Q) ~ . v~y~??"~c:-7)~~ I~ j~ it 'vi ,.- ~ E-·· . ... + -- .. -+-) --~. - + . I \
-t ----+ 1180 I ~- - -( ------ --} - ~."'"'---~ ~ .......• ~~ + I +
\ ---- ~ .'., 4-._"-----~.~ ... • ,'... \ ... I ~.. "...".
+
+ 1170
0 400 800 1200 1600 m
LEGEND: ~ -- silt, clay surface water
~ -D sand evaporation ground water flow
...
~ ?- ground water level weathered rocks
~ ~ laterite percolation
74
..
,. .
:i,
... " . ' .
.
"
i~' , .
!W ' •. i,e'.' .. ,
. -
~. i ;
'." "' .. " /. " ,'\,
). '>::,': -
"
.' ,
-April May June July
,
<
~ 8-101
I J 8 -102
- 8 -101 + 8-102
PRECIPTAT10N AND GROUND-WATER LEVELS IN TUMBI RFPR ARF A'·.
TABORA REGION WATER MASTER PLAN
.. :iaROK.~,"'S~oLT Aa
~'''''"'~' . PER ." .,> T.li.BY SWEDEN
." '", "i.,c>,
' ......... 31
:-" )
mm
50
40
30
20
10
o
maSl .... IlbO,U
... 1185,0
... 1183.0
4- 1182.0 + 1176,0
-1-1175.0
+ 1172,0
4-1171,0 -+ 1169,0
-t- 1168,0
-t- 1167,0
.... 1166,0
197811979
~ 8-101
o 8 -102
~<
" § «
8-101 <- 8-102
February March
I ; I
) ~, , I I
~) \1
1 I
)
, 1
, }
1 /
<
~ , <
~ ~ , ~ ,
75
::::1. ~ E.," oc~'o I-.=SF--+--=---=::::J"--c .. oc-o
+1154.0 l===================~P==================r~~================f=~========~==--~------~============1
+1153.0 .-=------1 lQ7q .1IlNllllDY FEBRUARY MARCH ... "
GROUNO WATER RECOROER INSTALLEO 1979-01-19
'''''1 -I +1153_0
TIOE FLUCTUATIONS
'::::: 1 ===:==: ~.-:== :J o 1. 14/0 1. 14/03. 14/0 4. 14/0 5.14/06. 14/07. 14/08. 24/0 9.24/0 10; 14/011.14/0 12.14/013.
1 FEBRUARY 1978
GROUND WATER VARIATIONS IN BH 106/78 (5-106)
TU,18I REPR. AREA AUGUST-JULY 1978-79
2.1 .4
76
Computed Maps of Tumbi Representative Area
In order to compare the computed maps of Tumbi representative area with known conditions in a convenient way, extracts of the general computed maps have been made for the area and the surroundi ng blocks. In the following each of the maps performi ng yi e 1 d, geology, 1 andform and 1 and surface wi 11 be di scussed.
Genera 1
In the computed maps, Tumbi representative area is represented by 11 blocks which is 11 km2 and consequently covers 4 km2 more than the area mapped on the topographic sheets, see Figure 6.9 This depends on the shape of the area. To be exact, only about 1/3 of the northern two blocks are occupied by the area and about the same situation is valid for the three southern blocks.
It shou1 d a1 so be kept in mind that the each block of the computed map 2epresents the average situation inside that particular km when it comes to properties like geology etc.
The Ground Water Potential Map
Accgrdin g to the computed map each of the 11 km 2 would yield 5 m /h. The presumpti ons for that is a depth to bedrock of 23 m a permeability of 10-5m/s and a static water level of 4.0 m see Table 6.66 Comparing those values which are average values estimated for the whole region where this geology prevails with the conditions at Tumbi the following can be noted:
a. The depth to bedrock is 34 m at the valley outl et BH 106/78 and only about 10 m higher up in the valley (apart from the depression to the west).
b. The well-test of BH 106/78 indicated a transmissivity of 2.0 x_~0-6 m2/s implying a permeability ~f 1.1 x 10 m/s.
c. The static water level at the valley outlet is about 15 m and still lower higher up in the valley.
The most important factors which makes the Tumbi area produce less deep ground water than the computed map promises are the permeability at the valley outlet which is about 100 times lower than the estimated value and the aquifer-thickness which is very small in the upper northern part of the valley. Consequently, the Tumbi basin is too small to be representative for the granitic areas of the region as a whole when studying the possibilities to extract deep ground water.
... tt' ,
, -. ~~.·.:.;·I ~~ -,
77
The Geology Map
According to the computed map the whole basin belongs to geology class 8;soil over granite. This agrees with field observations in the valley. The flat land which occupies the valley-bottom is too narrow to be classified as alluvium and the occasional occurences of laterite at the sides of the valley are also too narrow to be classified.
The Land Form Map
The Tumbi basin is here represented by outcrops and pediments undifferentiated which agrees well with the field observations, see photos.
The Land Surface Map
According to the computed map the Tumbi basin is occupied by village land. grass and woodland. This seems to be good judgement with respect to the actual condtions compare the photos.
78
EXTRACTS FROM THE COMPUTED MAPS LANDFORM AND LAND SURFACE; TUMBI REPRESENTATIVE AREA
LANDFORM
Legend:
1111111111111111111 778888888888999~999 8901234567890123456
(=) : F1 ood pl ain
(X) :
(> ) :
(&) :
( $ ) :
Peneplain
Mbuga
Pediment
Outcrop,
~?.5 ;;::) 4 ,-. ,-,-, ,;:.,' ..., .:..L~
.:. r :
~ ,-' :~; .:. I ',' ~ 1 ':. .. , .., .. -:.. .
.:..':' .::..
.- 1 , .... .:.. ~ '.'
;;:. c '~'.
Undi ff.
no soil
~ I] 1 ~(!U
12 i 1111:1111111 77 8 8 8888990999~ 89 4 ~?8S012345~
.-------------------~ I £. n t11'1 £. if: t1 ,:, L f. > £ > £ :1 £ * f, 1-1 I IMMMM£MM£PM££~£M£)£M! 1££M*£$£i:liM*£~>~£*>MI l£M*MMMI~~~££~:~·M~:*~·>£I I t'1 \'1 tri £ fi £ ><::.~ *;;.. f > Vi t1 N t'1 >!-: :> £ I ~*~·~*M~£~:£{~;~:M£~MM:> -r I£.'1:+.\ft1t~:~:f{.fi£{t1:1'> >£ '>1 :;: !'H1 :+: .> f. ill';'~ t·1£ '1: .~. t: t1 i i £ £ { ~ IMM££."£i*£££££f££££1 I f1 j'1 * t'1 ;'1 11 i~ ~ ::.-~: t:. i _'I £ .-.. > ~. > "': r /. ;f: ,-r 11 :f. £. M i·1 f * ';. ;+: £. £. ;.I.: ... :. >~: :' I I£MM£f£~:*'·fi£~:>f.**>~I I :f:I'lt'lN'+ ;;-::./·r'1£!1/1i.o', >~Mf* >[ IMi1iM~M£~£f>rl~£»~M*I I ~: £ 1'1 :t: 11 £ H:1 ~; ti f ;1 ..., ;l.: >- > :> ~ > I ;: -1: £ f. *f I'; :'1:'1).' t'l r- £ ';. t1·t. [ [. -f; f I I~~:£*~£M£»L>*M~£~f£I I [N~' *{f :+',:. {.: '" .,"> £:-- > £,f. >I: I I £ £ >t: 't' '"': *' :-1' !'1 > ~ f1;4-: t·t * :-- £ [ {. {. I ~ > f ;.' ,> V ~; I'~ ;; r1:: f, > t'1 £;, £ £ '; £ ! : >l:£ *::t:'"' !f:l'iI1±:.I."jNft1t1: .'.£> ',I [£~~*~Mt1£MM£M££{£££~r 1£~d1£. ££>££H-.:+:f.£:1N*f.:-1 i~11,~£MMI1£11M~~:MHMM*>MI IM)££MM*MMMM*MlMM)MMI r : .. ;>: £. > ~l i., >I: >t. > f :)( 11 £. :£ t" N N ~'1 t1 I if:: i: 1\-:: '-, t1 " ) ). H :1 i, t-1 f .'> t1 N 11 r I ;-. i.. [-I {,. 11 >t; " 11 i'1 1'1 > !'1 * f t-1 > > f-l r : ;. '" n l'1 if > 11"., 1111 :-. !111:' > :- flt'll ~ ___________________ w
LAUD SURFACE
Legend:
( ) : Vi 11 age
(> ): Grass
(*) : Scrub
(M) : Woodland
L.
79
EXTRACTS FROM THE COMPUTED MAPS GROUND WATER POTENTIAL AND STRUCTURES
TUMBI REPRESENTATIVE AREA
GROUND WATER POTENTIAL 1111111111111111111 7788888888889999999 8901234567890123456 Legend:
( -) : (> ): (=) : (+) : (M) :
0-1 m /h 2-3 m /h 3-4 m /h 4-5 m /h 9-12 m /h
STRUCTURES
Legend:
(+ ) : Li neament
2.22 2.21 220 219 -2-18 2.17 2-16 2.15 2.14 213 2-12 211 210 2.09 ;W8 207 206 205 2-04 2-03 202 2-01 ZOO 1.99 1-98
222 221 220 219 218 217 216 215 214 213 212 211 210 209 208 207 206 205 204 203 202 201 200 199 198
*-------------------* [==-===-+++-++-+)+=+[ 1==-===-+++-+----+==[ 1---==-+-+-+++-+-+)=[ I++-==++-+++++-+}++)I 1++-=++--N=»+++++-+1 1++)}-++=)++++++)+++1 1====++++=+++++»-)+1 1=====+++++++--+»+)1 1=====+++~+»)+->=1 1====»>=+- +»++++>1 1-==--++>+ --+>+---1 1}=-)++-+ --}-+»+}1 1===»+--++ >+++}+--I 1}>=>==+++ »+-+>-++[ 1++»>=-==»+»»>+-1 1+++>----}>++-}-+++-1 [+++}---)-+++--++-}+1 1+++---====++--»»>1 !=>----====++=++-}--I I+>-}»======-+--++>r [}--=========-++--++1 [-+H====+=====+--}--I 1+>MM===>==-===+-NM-I [+++H==-===-===+M+--I [++-M=-===--===>====[ *-------------------*
1111111111111111111 7788888888889999999 8901234567890123456
*-------------------* [ + I [ + [ [ + I I + [ [ + [ I r [ I 1
D [
1 I 1 I I 1 r [ 1 [ [ 1 [ [ [ [ 1 [ [ [ 1 I [ I I + 1 [ + I 1 ++ +++1 I + + I 1 + I *-------------------*
GEOLOGY
Legend:
( ):
( ):
(P) :
Alluvium
Laterite
Granite
80
EXTRACTS FROM THE COMPUTED MAPS GEOLOGY
TUMBI REPRESENTATIVE AREA
221 :::~ 0 21 '} 218 :? 1 7 ;;:: 1 ;:~,
215 ;2 1 4 213 212 ;;: 1 ! ~iO 20 Sf 208 207 206 205 204 ;;:03 202 201 ~OO 199 198
1111111111111111111 7788888888889999999 8~0123456789012345G
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81
2.2 NATA REPRESENTATIVE AREA
General
The area is a fl at basin situated about 15 km north of Nzega wi the outlet close the the Shinyanga road. The basin extends 4.3 km towards south and its maximum width is 1.8 km, see Figure 6.
The rather flat basin has a well defined water shed which is easily determined from the topographic map with the help of air photos. The drainage basin covers an area of 4.9 km2 • The a lti tude of the southern hi ghest parts reach + 1200 m a. s.1. , while the altitude of the valley outlet is about + 1150 m. gradient of the stream which occupies the middle part of the valley and dewaters the area towards north is consequently 1. 25%.
FIGURE 6.33
FLAT BASIN OF NATA REPRESENTATIVE AREA. PHOTO TAKEN FROM THE END OF PROFILE 6-108 TOWARDS WEST
82
FIGURE 6.34
VIEW TOWARDS NORTHWEST FRO~1 THE END OF PROFILE 6-108. t.JOTE THE POND THE WATER OF WHICH IS TRAPPED BY IMPERVIOUS LATERITE. NATA REPRESENTATIVE AREA
Land Use
Most of the basin is cultivated. In the lower portion in the north ri ce paddies are found but for the rest the main crops are maize, cassava, sorghum and sweet potatoes. Also ground nuts are grown here.
83
Geology
According to the geological map the southern half of the valley consists of granitic bedrock while the northern part is a formation belonging to the Nyanzian series. This seems to be dark consist of shales, phyllites and quartzites judging from the results of the drilling carried out. The contact zone is on the map visualized as a staircase descending towards east, each of the three steps are separated by faults running in north -southerly direction. The faults are on air photos recorded as very weak lineaments. The overburden consists mainly of sand and sil t. Outcrops of lateritic hardpan are found along the eastern slope. At the margin of this formation a few waterholes exist. The water is seeping out of the hardpan dnd becomes trapped by the lower 1 aying sil ty cl ayey material. These waterhol es carry water throughout the dry season. Furthermore, shallow waterholes are dug in lowest parts of the dry river course. The stream carries water only during the wet season .
FIGURE 6. 35
. --~,:--- .. -" "., ~
.:..y.. N A ~,'2, (0
, '--
EXTRACT FROM GEOLOGICAL DEGREE SHEET 28 NZEGA, NW QUARTER. DARK GREY TO THE SOUTH IS GRANITE. t1EDIUM GREY IS NYANZIAN AND LIGHT GREY SUPERFICIAL UNDIFFERENTIATED DEPOSITS.
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NATA REPRESENTATIVE AREA
( -
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5-317
-r-r+-______ ~/~~----~---~~--------+-------~------+9549 :f 5-211
: I
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,6-309 6-10S 5-316 I 0 0 5-416
J /1 6-3 0 o
6-109 o 5-315
5-415
1160
5-314 5-413
5-214 5-213 5-414
5-314
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DATE ~I~ ~!I~~~~--L-----------------------,------------------------ ___ -L ________ ~
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86
Geophysical Investigations (see Special Map Figure 6.37
The investigations at Nata comprises the following:
Resistivity:
Sei smics: Magnetics:
Resistivity Profiles
Profile 6-107 (Fig. 6.38) O-point UTM: Profile Direction: Profile Length: Resistivity Probe Spacing:
Additional Investigations:
Location and Siting:
Resul ts:
Profiles 6-107-109 Soundings 6-406-411 at BH 5-108 (124/78)
Profiles 6-205-206 Profiles 6-308-310
~530 N 90 300 m 50 m
Seismic profile 6-206 with the same O-point and length. BH 5-109 (125/78) and BH 5-318 at 300 m BH 5-314 at 470 m. Magnetic profile 5-308 starting 200 m W of probe 1.
The profile was sited about 500 m S of the outlet point and crosses the vall ey, see Fi g. 6.38. The small stream, which runs in the center of the valley is passed at 400 m.
The largest depths to bedrock were obtained at both ends of the profile, 50 m at probe 1 and 95 m at probe 7. Between those two points the bedrock level was found between 20 and 25 meters. The depths agree well with those obtained at the seismic investigation and the drilling. At probe 7 a 86 ohmm layer was indicated at 30 m depth which probably is fissured schist or gravelly valley fill. The major part of the overburden is rather compact clay and silty clay averaging 12 ohmm which becomes more gravelly with increasing depth, (see borehole record 5-211). The clay content of 20% however, seems to remain from top to bottom of the borehole. Low resistivity 3.6-7.2 ohmm sectionwise at the surface, indicates clayey wet material close to ground surface. The alluvial sand at the stream is according to probe 5 about 2 m thick and continues as top soil about 50 m on each side of the stream course. The ground water level is close to the ground level which explains the presence of low resistivity layers at the ground surface.
m.a.s.l.
+1160
+ 1150
+ 1140
+ 1130
+ 1120
+ 1110
+1100 T, IS' x100 341
340
339
f60GJ
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5-109 5-318 5-314
Ill" 125!78fiYVL
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200 400
.... - .. - _._-_ .. __ .--~ ..• ~.- .. -'-
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RESISTIVITY PROFILE 6 -107 MAGNETIC PROFILE 6-308
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.. /"-
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At the western end of the profile the resistivities are between 16 and 19 ohmm implying coarse material. The same material is found at probe 9 and 10 at 10 and 16 m below ground level respectively. At the drilling of 5-213 a silty gravelly layer was struck at 26 m below ground level and it is believed that this is the resistivity layer mentioned above.
The 65 and 72 ohmm resistivities obtained at probe 7 and 8 could be fissured bedrock and the large depth at probe 8 thus indicating the presence of a weakness zone. Close to probe 10 there is a lot of outcropping laterite. There is also a shallow pond there trapping water, which flows on top of the laterite. Being saturated the laterite does not show in the resistivity measurements.
FIGURE 6.39
RESISTIVITY MEASUREMENTS AT 600 M IN PROFILE 6-108. THE BACKGROUND SHOWS NATA BASIN TOWARDS SOUTH
1
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. ,~ • " ~ 2 , " 3 " t; " i ~ 5
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+ 1150 I I ~21~ e:1f ~ 142 j i. 50 ~ ~ I I I I I I I 1 V 5~ 2§ 5.0 4.8 t': I I I I I
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RESISTIVITY PROFILE 6 -108 MAGNETIC PROFILE 6-309
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Profile 6-109 (Fig. 6.41) O-point UTM: Profile Direction: Pro fi 1 e Length: Resistivity Probe Spacing:
Additional Investigations:
Location and Siting:
Resul ts:
91
5152 95481 N 900
550 m 50 m
BH 5-315 at 450 m (Probe 7). Magnetic profile 6-310 starting 200 m W of probe 1.
The profile was sited 320 m S of the previous profile 6-108, see Fi gure 6.37.
At the western part of the profile depths of about 50-60 m were obtained. They decrease to about 30 m in the middle and increase again to about 50 m in the eastern end. The deepest part of the overburden is varying between 22-29 ohmm indicating gravelly material when comparing the resistivities of the previous profil e.
On top of this layer is a more clayey layer averaging 6.6 ohmm.
The top soil resistivities are varying a great deal indicating material with varying clay and moist content. The drilling 5-315 was too shallow to contribute with any information about deeper strata.
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92
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PER SUNDBERGS V 1-3 5-16363 TABY SWEDEN f-icnc.c,c,-------
93
Resistivity Soundings 6-406-411
Siti ng
The soundings were carried out as a special investigation around BH 5-108 (124/78) in order to gain information about the stratigraphy of the immediate surroundings of the borehole. The same layout used around BH 5-206 (106/78) at Tumbi has been used; thus 6-406 was sited 3 m N of 5-108 (124/78), 6-410 50 m to the North, 6-411 50 m to the south, 6-407 3 m to the East 6-408 50 m to the east and 6-409 50 m to the west. Shallow borehole 5-210 and Borros drill hole 5-317 have been shown on the drawing. (See Figure 6.22 )
Resul ts
All six resistivity soundings indicated depths to solid formation of between 23 and 29 m. The indications were obtained about 5 m deeper than those achieved at the seismic investigations.
The Nyanzian bedrocks in the area consist according to the drillings weathered schist on top of siltstone which at about 24 m depth turns into harder grey schist. This transition zone has obviously been recorded at the geophysical investigations. Deeper on, at 42 m, the greyish schist becomes harder as the quartzitic content becomes higher. This fact is clearly indicated by a sudden increase in the penetration rate. Ground water was also struck in the transition zone. The overburden consists mostly of sand and gravel, see the record of drilling 5-117, with a moderate clay content. The weathered schist was struck and sampled at 10 m b.g.l.
The ground water level was indicated at· about 1.5 m b.g.l. at the time of the investigation and was recorded at about that level at the resistivity investigation. The portion of overburden below ground water level and the weathered schist and siltstone down to the transition zone at 25 m obviously comes out as one single resistivity layer of 2.6-5.0 ohmm. The low resistivity depends on the comparatively high conductivity of the ground water 190 mS/m.
)
~ v A 94 ".,,_
~ I~
400- 700 rnls
---------- ----------, ~--------------
400~700 mjs
700-1500 rn/s 4,6
700-1500 m/s
3000 m/s
*- -------- 1500=14E ~ 2500-3000 m/5
$, 2TOOm/s
-_ ... _--- ~--- .. ----.--- .-- -,-100 150 200 250
5 El '"---' --,-
37. 5
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95 Seismic Profiles
Seismic profile 6-205 (Fig. 6.43)
District: Topographic Sheet No. UTM of O-point: Profile Direction: Profile Length: Geophone Distance: Additional Investigations:
Description:
Nzega, Village: Nata 80/1 5152 95488 N 950
350 m 5 m Resistivity soundings 6-406-411 Deep boreholes 107/78, 124/78 Shallow BH 190/78. Borros hole 5-317.
The profile is located in the northern part of the Nata representative area 150 km north of Nzega town. The profile is crossing the valley and the river course at the new bridge (Nzega-Shinyanga road), 1 km south of the Village Nata. The profile is crossing the flat river plain which is covered by sandy-silty fluvial sediments. On the sides of the profile the soil consists of clay and silt.
Result
The thickness of the overburden is 15-20 m and the surface of the bedrock is rather flat. Two layers of different velocities are recorded. The top layer with velocities 400-700 m/s has a thickness of 7-10 m and might consist of dry clayey silt and sand. The other layer has the velocities 700-1500 m/s which is supposed to correspond with silt and sand below the ground water. The velocities of the bedrock ranges between 2500 and 3000 m/s which is representative for schists. Only three narrow low velocity zones have been recorded. See below.
Distance m Veloci~ m/s Remarks from O-point
20- 25 2000 120-125 2100 170-180 1500 BH 107/78 and 124/78
One borehole 107/78 was sited on the velocity zone 1500 m/s at 172 m where a small depression is found also. As BH 107/78 caved in another borehole was drilled close to No. 124/78. The result of the borehole coincides fairly well with the interpretation of the seismic profile. Thus the clayey-silty-sandy loose sediments show the same thickness. The dense half consolidated siltstone has a thickness of about 15 m. The hard schist is struck at about 24 m which differs from the seismic with about 2 m. The water was struck at about 40 m in BH 124/78 and the ground water was rising to finally about 0.5 m below the ground level.
;0 -1500 m Is
"#=- .. --~--
'B1!f=rtl-;E'?m hi - #t'!'i>il ~ 111 jl~ 'e:H[l C'
..... ~ '_I )-~-
350m
BH 124178
o
~1151,O
--- ---
2500-3000m/s m/s
T depth 54 m
200 m
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TABORA REGION
The United Reou'blic of Tanzania ~1inistry of \~ater Development, Energy and ~1inerals
PART OF TOPOGRAPHIC MAP SHEET No 80/1 1 :50000
International Bank for P.econstruction and development
TABORA REGION WATER MASTER PLAN
SEISMIC SURVEY: PROFILE 205
~ BROKONSULT AB ~ CONSULTING ENGINEERS AND ECONOMISTS
PER St;NDI3EAGS V 1~3 5-18363 TJiBY SWEDEN
DRAWlNG NO. 6.43
DATE
It It --• • ••
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TABORA REGION
The United Reoublic of Tanzania ~lin;stry of \~a.ter Development, Energy and t~i nera 1 s
515
:\~MabangtJ ,//~'~~.
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PART OF TOPOGRAPHIC MAP SHEET No 80/1 1 :50000
International Bank for P-econstruction and development
TABORA REGION VVATER MASTER PLAN
SEISMIC SURVEY: PROFILE 206
~ BROKONSULT AB ~ CONSULTING ENG!NEERS AND ECONOMISTS
DRAWING NO. 6 .. 44
PER SUNOOERGS v 1·3 S-!8363 Tii,SY swEDEN DATE.
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Seismic Profile 6-206 (Fig. Di stri ct: Topographic Sheet No. UTM of O-poi nt: Profile Direction: Profil e Length: Geophone Distance: Additional Investigations:
Description:
97
6.44) Nzega, Village: Nata 80/1 5152 95 488 N 950
300 m 5 m Resistivity profile 6-107 Deep borehole 125/78 Shallow BH 191/78, BH 16/79 Borros hole 5-314 and 5-318
The profile is situated 500 m south of the profile S-205 within the Nata representative area. It is crossing the course of the small river that is dewatering the area. The central part is covered by fluvial sandy silty sediments. The dominant soils on the valley soils consist of silt and sand as well. On the eastern side layers of hardpan formation is outcropping and the margin of this formation shallow well s occur.
Result
The conditions are here almost the same as in profile 205. The thickness of the overburden varies from about 30 m at the beginning of the profile to about 20 m along the rest of the profile. The surface of the bedrock is rather even. The top layer of the overburden has a thickness of 5 to 8 m and the velocity 350-600 m/s which corresponds with dry silt and sand. The underlying horizon with the velocity ranging from 600 to 1500 m/s is interpreted to
. consist of sandy-silty material below ground water level.
The bedrock is giving the same velocity as in profile 205-2500-3000 m/s which is suggested to be a schist. There is only one low velocity zone here 2300 m/s at 100-110 m. The borehole 125/78 was· sited on this zone which here according to the borehole log seems to be a depression. The top soil in borehole consists of silty clay-clay which is followed by more calcareous gravelly material probably loose sediments on the surface of the rather hard and well consolidated siltstone which here when it is gradually getting harder in the lower portions gives velocity as a weakness zone in the bedrock. It is underlied by the hard phyllitic schist. The water is struck at 16.5 m, i.e. in clayey silt and then at 41.8 m in the hard schist. The ground water raised to the ground level.
Comments
In the boreholes in this area the clayey top layers correspond to the velocity-layer 350-600 m/so The gradually harder siltstone towards the depth whi ch is consi dered to belong to the 1 ake sedi ments described in the description of the geology and the boreholes gives the velocities 1200-1500 m/so Finally the nyanzian phyllitic schist corresponds to the velocity 2500-3000 m/s which is normal for a metamorphic sedimentary bedrock.
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Magnetic Profiles
Magnetic Profile: 5-308 O-point UTM: Profile Direction: Profil e Length:
Location and Siting:
Results:
No anomaly was obtained. 34,000 gammas.
Magnetic Profile: 5-309 O-point UTM: Profile Direction: Profil e Length:
Location and Siting:
Results:
No anomaly was obtained. gammas.
Magnetic Profile: 5-310 O-point UTM: Profile Direction: Profil e Length:
Location and Siting:
Results:
99
5 151
0 N 90 500 m reading taken every 20 m
The profile starts 20 m W of resistivity profile 6-107 and is carried out in compliance with the 1 atter. See fig. 6.38.
The values are slightly varying aaout
5150 95484 N 900
750 m reading taken every 20 m
The profile starts 200 m W of resistivity profile 6-108 and is carried out in compliance with the latter. See fig. 6.40.
The values are varying about 34,000
5149
95491 N 900
850 m read i ng taken every 20 m
The profile starts 200 m W of resistivity profile 6-109 and is carried out in compliance with the latter. See fig. 6.41.
No anomaly was obtained. The values are varying about 34,030 gammas.
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2.2.2 Drilling
The following boreholes were drilled in the area: Three deep boreholes by the Schramm drill rig, 107/78, 124/78 and 125/78. The borehole 124/79 was a substitute for 107/78 which caved in. Five shallow boreholes by the CME rig 190/78, 191/78, 16/79, 17/79, and 18/79 and finally nine holes by the Borros rig: 5-314-318 observation pipes and 5-413-416 soil moisture-pipes.
Profile 6-205
The following boreholes were drilled in profile 6-205 and in the vicinity of BH 5-108 (124/78):
BH No. Distance Depth Remarks
107/78 172 m 69.2 Caved in * (Fig. 6. 46l 5-108 (124/78) 172 m 55.0 * (Fig. 6.47 5-210 (190/78) 10 m 45.6 N 5-108* (Fig. 6.48) 5-317 3 m 10.3 S 5-108* (Fig. 6.49)
* See attached BH descriptions.
The first and northermost profile shows a good conformity between the geophysical investigations (seismic profile 6-205 and resistivity soundings 6-406-411) and the drillings. The overburden is about 10 m thick and according to the SChramm drillings it consists of clay and silt probably with layer of cal crete and gravel. A detail ed sampl ing was made by the Borros Rig BH 5-317 and expressed that the topmost meters consist of clayey and silty sandy layers underlain by mostly sandy and gravelly sandy deposits. The loose deposits are followed by a light gray half-consolidated stratified siltstone which gradually is getting harder at deeper portions.
The surface of the siltstone was determined from the analysis of the Schramm drillings. In the control-hole made by the Borros rig the surface zone was sampled and the sample consisted of very weathered Nyanzian schist. It is possible that it can be interpreted as weathered strata of the Nyanzian schist intercalating with the siltstone. Consequently the siltstone should belong to the Nyanzian formation. Another possibil ity is that the Nyanzian schist found at the same level as the upper part of the siltstone could belong to material deposited in a river bed or to a layer of gravel and boulders of beach sediments in a lake where the finegrained siltstones had been stratified.
According to the samples analyzed the thickness of the siltstone hovlever, differs in the two deep boreho 1 es: It is about 28 m in BH 107/78 and about 34 in BH 124/78 which might depend upon the
I
I ,
101
difficulties in obtaining proper samples with this type of drilling. However, according to the penetration rate in both the holes a harder formation is found at about 42 m below the ground level which should correspond to the hard grey schist which is underlaying the siltstone and which is partly quartzitic.
F IGIJRE 6. 45
RIG 48 DRILLING BH 124/78. VIEW TOWARDS SOIJTHWEST.
I:
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102
The detailed information on BH:s 107/78 and 124/78 are repeated here from Volume 6A for completeness.
1. Borehole No.
2. Siting:
107/78, WMP No. 5-107
The representative area at Nata is a flat basin situated about 15 km north of Nzega with the outl et towards north-east close to the Shinyanga road. The basin extends 4.3 km towards the south and its maximum width is 1.8 km. See BH 107/78:1 (topographic sheet 80/1).
The rather flat basin has a well defined watershed which is easily determined on the topographic sheet with the help of air photos.
According to the geological map, geological degree sheet 28 Nzega NW, the bedrock in the northern part of the valley consists of a formation belonging to the Nyanzian series which towards the south is succeeded by granite. The contact zone is visualized as a staircase descending towards east, each of the three steps are separated by faul ts running in north-southerly direction. The faults are found on air photos as very weak lineaments. The overburden consists mainly of sand and silt. Outcrops of lateritic hardpan are found along the eastern slope. By the edge of this deposit a few waterholes exist. The water is seeping out of the hardpan and becomes trapped by the lower lying silty clayey material. These waterholes carry water throughout the dry season. Furthermore, shallow waterholes are dug in lowest parts of the dry river course. The stream carries water only during the we t sea son.
Two seismic profiles have been carried out in the no;'thern end of the valley, 6-205 is the northermost one with a length of 350 m. 6-206 was sited 400 m south of the previous one. The length of the profile is 300 m. Resistivity profile 6-107 and magnetic profile 6-308 are running parallel to 6-206. Resistivity profile 6-108 and magnetic profile 6-309 were sited 300 m south and parallel to the previous one. Resistivity 6-109 and magnetic
3. Location:
4. UTM:
5. Level s:
6. Drill ing detail s:
7. Water levels:
8. Descri pti on of profile:
m 0.0- 1.2
1.2- 5.8
5.8- 8.8
8.8-10.4
10.4-14.9
14-9-18.0
18.0-25.0
25.0-38.7
103
differences in structure comparing to the and parallel to 6-108. No promising magnetic anomaly was recorded •
• One borehole 107/78 was drilled on the weakness zone in seismic profile 6-205. this hole caved in, and it was replaced by another hole 124/78. Furthermore, a few electric soundings have been performed close to BH 124/78 in order to investigate the relation between resistivity and transmissivity of the formation.
Nata, Nata Division, Nzega District. Seismic profile 6-205, 172 m east O-point.
M.A.S.L. Ground level: Top casing:
Depth: Water struck: Water level: Casing plain: Cas i ng slotted: Uncased:
Control date m below top casing:
See 107/78:2
Dark greyish clay.
1151. 0
69.2 m 38.7; 50.9 m 8.5 m
Dark greyish silty sandy clay.
Light brown silty gravelly sand.
Gravel of quartz, weathered granite and greyish soft silt-stone.
Greyish soft half consolidated siltstone wi th cal crete.
Gradually harder silt-stone - shale with some calcareous layers and some quartz.
Greyish brown rather soft shale.
Greyish harder shale.
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till
,
38.7-47.9
47.9-49.4 •
49.4-55.6
55.6-69.2
9. Yield and well tests:
10. Geophysical
1l. Well log: See 107/78:1
12. Water analysis:
13. Remarks:
104
Grey hard schist inter1ayered by greyish brown soft sha1 e.
Grey hard schist with quartz seams.
Brownish and grey quartzitic schists.
Greyish hard schists.
Yield: Well test:
Seismic: 6-205 see Vol. 7
Comments: The well log measurements could not be carried out because the boreho1e caved in but a comment should be made on the penetrati on.
The penetrati on is here very fast down to about +1110 m, 41 m below ground level. The speed is ranging between 2-3 min/1.5 m to 8 min/1.5 m. Below 41 m the penetration changes abruptly to 37-40 min/1.5 m, corresponding to the change of the lithology, from si1tstoneshale to hard schist. The increasing amount of quartzitic bedrock is ref1 ected by the slower penetration about 60 min/1.5 m below +1093 m.
See 107/78:3
The boreho1e caved in.
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+ 1130
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+ 1090
+ 1080
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GL +11510
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PENETRATION RATE (min)
o 20 40 60
J 1
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l~ .~
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DRAWING NO. 6.46
DATE ~L-________________________ -. ______________ -L ____________ ~
r:Ql:c..Iohnson 19856
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106 107/73
REG10N: Tabora LOCATION: Nata ............................. . " ..................... .
DISTRICT: .••...... ~~~9? ........... . 107/73 (WMP) ~ BOREHOLE NO: ......••.•.......•. . .
Oa te _________ _ 3/9/73
Conduct
Turbidi
Colour
Calcium lC~ mg/1 _____ _
!:1.ajnes i ~m~..:.:m2g!..../~1 ______________________ . __ _
A 1 ka 1 i ni ty meqv /~1 ___ .
Su 1 pha te . (504) m..::g"-/_l ____________________ .
_~h..l.()~:..i de.JS_1LIll.9j_1 __
].t-o~.1~eJ_.f1191.l_. __ . ___ . _ ____ ....Q:.2.3 _______ __ . ____________ _
Iil t~~te __ LN.LmllLl __ . _______ .2 . .2 _______ . EJ . .l!.0ride J£) mg/l 3.0
1. 22
~I-manganate ya 1 ue mg/1 __ __ 9.6
3.4 Silicate (5iOZ) mg/l ~~~---------
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1. Boreho 1 e number:
2. Siting:
3. Location:
4. UTM:
5. Levels:
6. Drilling details:
7. Water levels:
8. Descl"iption of pl"ofi1e:
m 0.0- 1.2
1.2- 5.8
5.8- 7.3
7.3-10.4
10.4-22.6
22.6-36.3
36.3-44.8
lG7
124/78 WMP No. 5-108
Description see BH 107/78. As BH 107/78 collapsed before it was cased, mainly because of engine problem it was decided to drill another borehole close to 107178.
Nata, Nata Division, Nzega District. Seismic profile: 6-205, 172 m east O-point.
5153 95491
M.A.S.L. Ground level: 1151. 00 1151. 52 Top casing:
Depth: Hater struck: Hater level: Casing plain: Casing slotted: Uncased:
Control date
10.09.78 14.11.78 19.12.78 25.01.79 06.02.79 20.02.79 27.02.79
See 124178: 1
Dark greyish clay;
53.9 m 39.3 m 4.57 m 0-37.5 m 37.5-43.6 m 43.6-53.9 m
m below top casing
3.87 1. 13 1. 28 1. 17 1. 10 1. 00 1. 00
Dark greyish si1ty sandy clay.
Light brown silty gravelly sand.
Gravel of greyish soft siltstone and calcrete.
Greyish soft half consolidated siltstone with quartz.
Gradually harder siltstone with quartz.
Greyish brownish hard shale.
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9.
10.
11.
12.
13.
44.8-47.9
47.9-53.9
Yield and well tests:
Geophysical profil es:
We 11 log: See 124/78: 1
Water analysis:
Remarks:
108
Dark grey hard schist pieces of grey shale and quartz.
Grey hard schist with some quartz.
Yield: 2.3 m3Jh Yield test by'airlift for 12 hours.
We 11 test:
Seismic 6-205 (see Vol. 7)
No log was carried out. The penetration rate is almost identical to the one made for BH 107/78.
See 124/78:2
No well test could be carried out because the area was flooded.
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m,o.s.L + 1150
+ 1140
+ 1130
+ 1120
+ 1110
+ 1100
BH 124/78 (5-108) re +1151,5 GL +11510
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PENETRATION RATE (min)
o 20 40 60
DRAWING NO.
:l m DATE
6.47
~L-___________________________ _.----------------~----------------~ I"'<fl: .. mhnson 7063e
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Tabora REGION: ............................. ~
DISTRICT: ... ~?~9? ................. .
Date
Conductivity mS/m
Turbidity
Colour
pH
Total Hardness meqv/l
Calcium (Ca) mg/l
i1agnesium (1-1g) mg/l
Alkalinity meqv/l
Sulphate (SOil) mg/l
Chloride (Cl) mg/l
Iron (Fe) mg/l
1>1 a n 9 a n e s e J.liI:Il mg /,-1:......-__
.riitraJ:~~/l
Fluoride (F) mg/l
27/12/78
190.
10.
10.
8.2
1. 40
11.2
10.2
17.44
9.
76.0
0.08
0.20
1.0
Ammonia (N) mg/l 0.37
!'ermanganate Value mg/l 4.8
Silicate (5i02) mg/l 5.1
110 124178
LOCA Tl ON: .•. N.a.t.a ...•.....•. ; •
BOREHOLE NO: 1.2.~ZZ~ ,(~r!~) .....
111
+ 1151.8 Y- %
Soil analysis.
BH 190178 (5-210) 100
mbgl \;1151.1 50 0 12
"~ 36 o 0
00
6 0 00 00
0,001 0,01 0,1 10mm
13 o 0
25 00 o 0 Soil analysis. 37· 00
o 0 %
WL 100
1 ? 100
1 10 0
2-1 14 o 0
38 o 0 50 , 26~ 10 0
16 25 5 ; o +_",l<'.I:(v 9~avelly ,sanJ I 0
o 0 0,001 0,01 0,1 1 10mm n M 10 0
3 o 0 15 39
00 o 0 loo
00 e 4 ,00
16 o 0
28 40 100 00
00 00 00
00 loo
5 00 o 0 29~ 17 41 00
10 0 00
00 00
6~ L-
30 -r:-::l 18 t-=J 42E
00
~ 00 o 0
00
7 19 31 43 00 10 0
o 0
00 00
8 20 32 00 44 - % Soil analysis.
00 100-
9n
00
50 J %
SoH analysis. "D 33 45 ! 19 '::C;: 00 o~ 22 26
sandy silt .'. A 0,001 0,01 0,1 10mm
10~
351
22 34 00
o -l----"!.<;Y-"Y sili:i fond i ~ loo 00 I
0,001 0,01 0,1 1 10mm 11
00
23E
35 ---J 0 0 00
o 0 00
ttJ 00
12~ o 0 00 I DRAWING NO. n 36 . 6.48
OATE
It.,.
." t 1; ... III
t a
mg bl
0
1 -
'-2
3
4 -
5 -
6 -
7 -
8 -
9 -
10 -
'" a. • ~ 1151.0 ~
(f)
1. 10,8
2. 16,3
11
~ 8,56
I--
00 ~ 5,35
0 0
0 0 5.
0 0
0 0
0 0
0 0
4,3
0 0
0 0
0 0
0 0
0 0
0 0
0 0
-w 6. 7,37
I 112
% Soil analysis.
100 1.
50
75 sand
0 0,001 1 10mm
100 2.
50
75 sand
0 0,001 0,01 0,1 1 10mm
100
50
0
3.
72 sand
0,001 0,01 0,1 10mm
100 4.
50
0 , 36 40 I
!:::::::;:=-~sa~,n1.'dJiy .. ~ 0,001 0,01 0,1 1 10 mm
100 5.
50
o ~:::::;::::::::S~~~ 0,001 0,01 0.1 1 10 mm
1:: 6 .---" :~~i:t~~ ,-_-"20 .-~~-. 42 I
o dae .~.~ 0,001 0.01 0,1 1 10mm
DRAWING NO. 6,49
DATE
~, .
113
Profile 6-107, 6-206
The following boreholes were drilled in profile and in the vicinity of BH 5-109 (125/78):
BH No. Distance Depth Remarks
5-109 (125/78) 105 m 49.5m (Fig. 6.50) 5-211 (191/78) 9 m N 5-109 38.0m * (Fig. 6.51) 5-212 (16/79 ) 10 m S 5-109 33.5m 5-314 350 m 3.6m * (Fig. 6.52) 5-318 2 m N 5-109 5.2m * (Fig. 6.53)
* See attached BH record with soil analysis.
The depth to the Nyanzian formation achieved at the drilling of 5-109 (125/78) coincide well with the depth obtained at the geophysical survey. Comparing the drilling at the valley outlet the clayey silty portion of the overburden is richer here at the sacrifice of weathered schist and siltstone. The CME drillings Nand S of the deep borehole showed 12 and 7.5 m thicker overburden respectively. Analysis of samples collected at the drill ing of 5-211 (191/78) showed clayey silt with increasing content of gravel towards the bottom.
The undisturbed samples collected at the drilling of 5-315 show that at least the upper 5 m of the overburden is fai rly heterogeneous with interlayering gravelly layers, probably of alluvial origin. At about 5 m depth the material became very compact, thus 1 imiting further drill ing.
The results from the drill ings of 5-314 on the eastern bank of the stream showed more homogenous material - clayey silty sand dOl~n to about 3.5 m when the material became too compact to allow further drilling.
, . !.
1 ; :
r. !
I I I I I I 1
1.
2.
Boreho 1 e number:
Siting:
3. Location:
4. UTM:
5. Levels:
114
125/78 WMP No. 5-109
Description see BH 107/78. The borehole was sited on a weakness zone found in seismic profile 6-206.
Nata, Nata Division, Nzega District. Resistivity profile: 6-107, 102.5 m east O-point. Seismic profile: 6-206, 102.5 m east O-point. Magnetic profile: 6-308,302.5 m rest O-point.
5152 95489
M.A.S.L. Ground level: 1153.22 Top casing: 1153.57
6. Drilling details: Depth: Water struck:
63.1 m 16.5; 41.8 m 0.0 m
7. Water levels:
8. Description of profile:
m 0.0- 1.2
1. 2- 2.7
2.7- 4.3
4.3-11.9
11. 9- 16. 5
16.5-18.0
18.0-21. 0
Water level: Ca sing p 1 a in: Casing slotted: Uncased:
0-19.5 m 19.5-24.4 m 24.4-63.1 m
Control date
19.12.78 02.01.79 09.01.79 16.01. 79 25.01.79
m below top casing
0.95
31. 01. 79 07.02.79 16.02.79 27.02.79
See 125/78: 1
Dark greyish clay.
Light greyish silty clay.
Whitish clay.
Light brown clay.
0.92 1. 00 1. 07 0.98 0.90 0.80 0.75 0.00 (overfl oa ti ng)
Silt with calcareous hard nodules, calcrete.
Greyish clayey silt.
Greyi s h clayey silt with some pi eces of quartz and brownish soft shale.
(.
J
9.
10.
11.
21.0-24.1
24.1-25.0
25.0-32.1
32.1-40.2
40.2-44.8
44.8-57.0
57.0-63.1
Yield and well tests:
Geophys i ca 1 profiles:
Well log: See 125/78: 1
115
Silt with pieces of dark greyish soft si1ty shale or siltstone.
Grey hard shale. Schist and calcareous nodules.
Samples disturbed by rotafoam.
Oark greyish schist partly quartzitic.
Dark greyish schist with pieces of quartz and ferruginous minerals (hardpan).
Dark grey schist almost phy11ite.
Hard dark grey schist.
Yield:
We 11 tes t:
4 m3/hr tested for 12 hrs water level recovered 25 minutes after pump stop. Aquifer test, step drawdown test. See 125/78:2 Safe Q = 1.1 x 10-
43 m3/sec.
T = 6.5 x 10- m2/sec. S = 6.0 x 10-4
Three well tests were carried out in this boreho1e, two step draw-down tests dated 07.02.79 and 16.02.79 and one aquifer test dated 08-09.02.79. The 6th step in the draw-down test dated 16.12.72 has been chosen when calculating T and S. No draw-down in the observation holes was noticed.
Resistivity: Seismic: Magnetic:
6-107 6-206 6-308
(See Vol. 7) " "
Comments: The penetration in this hole is a bit slower through the everburden and the upper part of the si1tstone and shale than in the other boreholes in the area, 107/78 and 124/78. The penetration rate is stepwise increasing down to about 40 m b.g.1. +1113, where the bedrock consists of the Nyanzian schist which here seems to have intercalating layers of.hardpan (murram) with quartz pieces. Deeper down at +1113 the deposits are harder with rates increasing to 180 min/1.5 m.
The increasing density downwards of the metamorphic sediments is shown in the SP and resistivity logs.
The temperature curve is rather constant at 27.0-28.80C with three local peaks going up to 32-330(, which might indicate water-bearing zones in the laminated sediments.
"I f
fl .
q . I
I
I I I I I I I , I I
12. Water analysis:
13. Remarks:
116
The uppermost one, at +1134, can coincide with water struck at 16.5 m i.e. +1136 m. The next one, at +1116, with a depression in the resistivity curve at +1135 (0.035 K ohm m) and finally the deepest one at +1105 m is coinciding with the resistivityO.045 K ohm m almost at same level.
The reactivity of the temperature sound is a little slow which could explain the difference between the levels of the water struck and the temperature maxima.
See 125/78:3
rn.os .L
.. 1150
.. 111.0
.. 1130
1120
.. 1110
.. 1100
BH 125/78 (5-109)
I LC=1 c
Te + 1153.5 GL +1153.2
W.L.
W.S.
LlrT 5 DIsturbed
li~
PENETRATION RATE Imlnl
20 40 60
J , i
~ I~~- I 90 ---i
~~ g !
.. 1090 I E:a 180 "0
1160
SPlmvl
o 20 40 60 80 100
-rr-Il-I ! i I , I
iT I 11 ; , ;--J
117
RESISTIVITY Ik ohmml TEMP ICOI
o 0.1 0.2 20 r30 1.0
. I
I
I I I
I I I
I
I I
c-
:
I
I ,
I i !
~ I :> , I I
BORE HOLE 125/78 WITH WELL LOG
r~ EHilOHO .. .JSULT tU;! ~ CONSULTING ENGINEERS AND ECONOMISTS
DRAWl NG NO.
P::R S~:r08::RGS v 1-) 5-18353 TA BY SWEDEN DATE.
6.50
·-.i .....
I f~.·1 ,~,
I it; I "'.
I I I I I I I I I I J
I
118 125/78
REGION: Tabora Nzega -Ndogo ........................... LOCATION:
DISTRICT: Nzega . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125/78 (WMP) BOREHOLE NO ••••••••••••••••••••••...
Date~ _______________ ~1~6/~1~1~/7~8~_
Conductivity m S/m 140.
10.
Colour 5.
pH 9.1
Total Hardness O1eCjv/l . ___ ... _2_._9_2 ___ __
43.2 .•. _-- ----_._.------
9.3
f~ 1 c i um j Ca) mg 11
1:1a_gne-"~U·1g) O1g/l ------ ------------- ---Alk~linity O1eqv/l 10.00
_Sul£.~~te (S04Lmgl.l__ _2_8. __
_ ~h..l~jj_~CflLm\l.LL _______ 77 ~ ____ . _____ ._. ______ _
l>~(! e lrl18!.l ______ .. ___ .2.:. 05 ______ .. __ _
I·langanese (i·If1.Lr11.g/1 0.10 ---- -~------ ------ -----_.-. ----- --._----- ._ .... _-----._--_.- -_.-----
i~i..0:~e_j!'il.rn.8.( 1 ___ 1. 6 ---------------------- ------.------
Fluoride (F) mg/l 0.4
Alllllonia (N) O1g/l 0.4
Permanganate Value mg/l 7.2 -------- ._----
Silicate (SiOZ) mg/l NIL
s~c:.? -~. -,...., -- .... - -, ....... lJr< .. / .... Jj-Ul..n,i\ I t.:; I ;,(, bH i 25/78
DATE 16/02/79
1st Step 2nd Step 3rd Step Time Sw Q S I S
Q min. VI Q w m m3/hr In i m3/hr In m3/hr
0.19 \ ,
1 0.65 I 1.35 2 0.16 I 0.67 i 1.42 3 0.62 I 0.69 i 1.48
. 4 0.83 ! I 0.71 1 .51 5 0.91 0.96 I 1. 52 6 0.97 1 . 13 I 1 .52 7 1.00 1 . 19 . 1 .53 8 1 .03 I 1 .25 . 1. 53 9 1.04 1 .22 , 1. 53
10 1 .05 I 1 .22 , 1.58 12 1.08 1 .20 , 1 .62 14 1. 29 1 . 17 I 1.66 16 1. 49 1 .13 ' 1.59 18 1. 54 1 .12 : 2.08 20 1. 55 i. 12 2.22 , 25 2.19 1. 10 2.25 30 0.83 1 .08 ' 2.43 35 0.74 1 .19 2.88 40 0.69 1.34 2.91 45 0.67 1. 32 2.85 I 50 0.66 1. 30 3.12 \ 55 0.65 1.30 3.15 60 0.65 1. 31 I 3.15 I
I
6 Sw 0.65 0.66 i 1 .85 I Q average 0.6?3 0.730 1 .287
_ ... -_ ...
;'--:-',S' .......-"".-:' ~ ..
4th Step Sw Q In m3/hr
3.26 3.43 3.52 3.59 \ 3.63 3.68 3.68 3.92 4.06 I 4.33 4.61 \ 4.67 4.70 4.74 4.77 4.84 5.30 5.39 5.36 5.39 5.56 I
5.62 5.81
2.65
2.031
'!:~ -,.' ',,' ~ ...:.. . ~~-' ,:.:..
5th Step S
I. Q w m m3/hr
5.91 5.92 5.95 5.96 , 5.97 I , 6.05 1
6.09 I 6.13 I 6.14 6.26 6.42 6.53 6.58 6.60 6.61 6.66 6.68 I 7.07 7.13 I 7.18 7.89 I
8.25 I 8.32 i 2.51 I
-~ ___ ~"'l'f" J ~--=-.'- .~,,;:;,:,~:::, .:~
6th Step Sw Q m \ m3/hr
I I
8.34 : 8.35 I
8.37 ! 8.37 I
8.39 ' 8.41 8.41 8.41 8.42 ' 8.45 8.47 : 8.48 i 8.50 8.49 ' 8.55 I
8.62 8.63 ' 8.63 8.86 8.90 8.91 8.84 8.81
0.49 ,
~
~
<!)
N en '-
" CtJ
2.86 L_ 3.211 _ ...
T"· .•.•
':~';: :.
, !,
,
------. -.' ~ , ,
-. -----. ~·I· '~, ,
-I -,
Time Min
0 1 2 3 4 5 6 7 8 9
10 12 14 16 18 20 25 30 35 40 50 60 70 90
120 150 180 240 300 360 480 600 720 840 960
1080 1200 1320 1440
120
BOREHOLE 125/78
AQUIFER TEST
8/2/79 - 9/2/79
Draw Down Di scharge
Sw sobs m3fhr
m m
0.00 0.00 0.20 0.55 0.79 0.90 0.98 1. 02 1. 05 1. 07 1. 08 1. 09 1 . 11 1.11 1. 13 1.13 1. 13 1.11 0.92 0.00 0.79 0.76 1.29 1. 20 0.05 0.75 2.01 2.38 0.06 2.78 0.02 1. 00 5.90 0.00 5.93 0.00 2.80 7.77 0.01 2.73 9.43 0.01 3.77 9.73 0.01 2.92
10.89 0.00 3.16 10.91 0.06 3.57 11. 12 0.04 4.01 11.19 0.01 3.42 11. 71 0.04 3.55 11.62 3.54 11.64 4.26 12.99 3.52 13.49 3.69
125/78
Remarks
r = 9 m
Q = 3.3 m3/hr
~l~!': 'j.' .
Il!! ...
"~I! : !mtj .
Ili! I~i 11.
Time min
0 1 2 3 4 5 6 7 8 9
10 12 14 16 18 20 25 30 35 40 45 50 55 60
120
Step ~sw S\1 rn m
1 0.65 0.65
2 0.66 1. 31
3 1. 85 3.16
4 2.65 5.81
5 2.51 8.32
6 0.49 8.81
B ~ 4660 ~ 4.7xl03
121
RECOVERY DATA IN BH 125/78
Aquifer Time Step draw-Sw m min down Sw m
13.49 0 8.81 7.76 1 5.84 7.10 2 3.38 3.61 3 2.12
2.70 4 1.65 2.16 5 1. 31 1.83 6 0.95 1.55 7 0.93 1.38 8 0.81 1.24 9 0.74 1.12 10 0.67 1.00 12 0.58 0.90 14 0.51 0.83 16 0.47 0.78 18 0.41 0.74 20 0.39 0.65 25 0.34 0.57 30 0.30 0.53 35 0.26 0.50 40 0.24 0.46 45 0.21 0.43 50 0.19 0.41 55 0.17 0.39 60 0.17
+0.05
125/78 NATA
JACOS'S ',lETHOD
0 sw/O SO CQ2 m3/sec sec/m2 m m
0.000173 3757 0.81 0.22
0.000203 6453 0.95 0.30
0.000358 8827 1. 67 0.93
0.000564 10301 2.83 2.32
0.000794 10479 3.70 4.59
0.000892 9877 4.16 5,80
sec/m2
C ~ 7287500 ~ 7. 3xl06 sec 2/m 5
125/78
Sw m
1. 03
1 .25
2.60
4.95
8.29 q qr;
.i 1154.0
BH 191/78 (5 -211)
.. 'tf""" o .. v 12 I 3 --W.9
o 0 o 0
o 0 13 i 0 0
001 w.s. %
Soil analysis
100 I 0 0
2 --1 ~ ~ W i 14
o 0 50 ~
~ o 0
I , Soil analysis 12 30 35 %
3 -l ~ ~ clo sand cavel 15 0 0 0 100 -r
0,001 0,01 0,1 10mm I , o 0 I
soJ
H;~ 16 t= 24 __ clayey 00
o , , 0,001 0,01 0,1
5t- 17~ 0 10 0 I
o 0 r-
6t
o
18t o 0
o 0 ~O 7 -fa 0 19
1 % Soil analysis o 0
,_100
1 "~}
8+ -I w:J . 20 43 o +---- c\oyey sit t .
"~ 9+ ~ 0,001 om 0,1 10mm
00
o 0
10-100
1 22 o 0
001 I--o 0
11 --1 0 0 j 23 -l===j
12B ,,8
24
25 00
o 0
26
00
27 00
" 28 loo
silt
10mm 10 0
29 o 0
30
o 0
31
10 0
10 0
32
10 0
10 0 33
ko
o 0
34
loo
35 -~ 00
00
35 B
% 100
Soil analysis
122
36 50
W5 o I cl~yey i :"'\\ I
0,001 om 0,1 10mm
37
38
% Soil analysis
100
~ 50
0 clayet silt
0,001 0,01 0,1 1 10mm
% Soil analysis
100 ~---------,
o 0 ~ 501 ~ 19 27.30 o I ci°Y~ gro,vell Slit o 0
0.001 0,01 0.1 1 10 mm
o 0
o 0
I QRAWING NO. 6,51
DATE
.~
I 1
I
I I I I
.~
.,~i4 ......
s
+1153.9 BH 5-314 '"
I i mbgl + 1153,1 0
Vl o --l-''----1
% Soil analysis,
100 -.--~-11.
50
Ci E§ Eo)) .cc 00
25 35 36 o cl~L_~_--=sa~n~dO-.--1
0,001 0,01 0.1 10 mm
100 ---.--~-.----.. ---
50
o
2,
16 cia e
0,001 0,01
14 silty
I
0,1
42 sand
10mm
, 123 I
% 100
50
Penetrot ion rate
o 15 30 bumps/20cm J---+-~-'
I..--~ 18 28 o cia ey sil !Y
29 sand
0,001 0,01 0.1 1 10mm
DRAWING NO, 6.52
DATE
llii'i ,
11: 'I,
~: ,I
i ~ I' I',
i: li ;
, , ! ~
1= !:! ~ ro ffi
+ 1153,9 BH 5- 318 '"
I a. '" '" EE EU
0. 0 0 Ft:
mbgl + 1153,1 E El/) 0 .!:c .!::J
(/) 00 01/) 0
I 1
2
3
4
5
% 100
50
1.
o 0
00
o 0
5.
Soil analysis
1.
37.0 55
4,20
12,7 9,09
14
19 72 o --r_<::J(]Y~:L ____ E,Ql'1d
0,001 0.G1 0,1 1 10 mm
100
'12~-~"--"'---""'-""'--50
1.-_--14 36 o .... _$Cl.Y..'Y_, __ §(J.l'1'J._.
0,001 0.G1 0,1 1 10 mm
100 3,
50
65 o .. --,-.. ____ s~ndy-gr,a.vel
0.001 0,01 0,1 1 10 mm
i 124
% 100
50
o
100
50
Penetration
0 15
4.
0,001
. _. 5.
rate
30 bumps/20cm
500/18 cm
40 sand "'-'-,-~--
10mm
t---~19 60 o + ____ c::I~ye~.-r sand
0,001 0,01 0,1 10 m m
DRAWING NO. 6,53
DATE
~L-________________________________ .-______________ L-____________________ ~
Mo..Iohnson 7~e38
¥
I , ~
t I , ~ , .~
, ( , I I
I I
I
I I
•
125
Profil e 6-108
The fo 11 owi ng holes were dri 11 ed in the pro fil e:
BH No. Distance Depth Remarks
5-316 100 m 3.0 See attached BH record with soil analysis Fig. 6.54.
5-214 (18/79) 380 m 36.6 5-213 (17/79) 530 m 44.2
The two CME holes were drilled on the eastern slope where the resistivity survey indicated large and varying depths to solid rock. The drillings confirmed the geophysical indications as comparatively large depths were achieved 36.6 and 44.2 m respectively. Studying the geological map the contact between the Nyanzian formation and the granite is not very far to the south, moreover, a couple of minor faults running in N-S direction appears to be connected with this contact. One expl anation to the 1 arge and varying depths to the sol id rock at the eastern part of th profile might be that a fault belonging to that system is crossing here. The gravely deep portion of 5-213 (17/79) should presumably be interpreted as weathered schist. The upper portion is mainly clayey silty while the topmost five meters most probably consist of laterite.
At the drilling of 5-214 (18/79) there were also signs of weathered schist at depths below 12 m but calcrete is also mixed into a large extent. It is impossible to determine from the cutting if weathered bedrock was struck at this particular drilling. The topmost 3 m seems to consist of laterite. BH 5-316 was a shallow hole carried out by means of the 8orros equi pment. It reached 3 m only where a too hard formation made it impossible to continue. The soil analysis showed a very sandy material with a fairly low clay ccntent of about 15%.
h
l.\1'l':J: "','1' "':. \
wt' '11
;11 " '/
I' I, )'
i')
~i Jl.
mbg o
1
2
3
I .
%
100
50
0
100
50
0
BH 5-316 + 1155,5
I '" Cl. E
,;1154,9 0 if)
~
Soil analysis
1.
cla e
0,001 0,01
2.
0,001 0,01
'" 0.
e E o
EUl .cc 00
23,1 21.7
13,4
sand
0,1
13
'" EU o E't: .c::J OUl
I
r 19
55
10mm
55 clayey sand
0,1 lOmm
. 126 I
Penetration rate
o 15
100/18 cm
DRAWING NO.
DATE
6.54
i~ .... ~~,::
" .. .. Iq
--. I~ ~,
" . , at ~r
it ~, ~,
M if' ,
Wf
;(
>1
I ~l
~l
127
Profile 6-109
The profile contains only one borehole:
BH No. Di stance Depth Remarks
5-315 250 m 2.70 See attached BH record with soil analysis Fig. 6.55.
The drilling was carried out on the eastern bank of the stream and reached 2.7 m b.g.l. where hard formation was struck. The stratigraphy shows great similarities with that of 5-315 with gravelly layers interlayering finer material •
i 128
BH 5-315 (l}
+ 1157,5 2( Ci. (l}
EE EU Penetration rate I
a. " " E EVl E't mbgl +1157,1 " .cc ..c;:J 0 15 30 bumps/20cm
(f) 00 OVl 0
8,13 10
o 0 t o 0 3,85 o 0
2 15
o 0 3. 6,91 1 -4. 8,57 100/8cm
".
% Soil analysis.
% 100 100 3.
---1.
50 50
20 60 18 40
0 clayey sand 0
clayey sand --I I
0,001 0,01 0,1 10mm 0,001 0.01 0,1 10mm
100 100 2. 4.
50 50 44 sand
12 32
0 0 c aY-"t- gravell Y
0,001 0,01 0.1 1 10mm 0,001 0.01 0,1 1 10mm
DRAWING NO. ~ w
'" 6.55
j ~ DATE ~~~ ______________________________ .-______________ J-__________________ ----
reoJOhnson 1VC3e
J
129
Soil Moisture Measurement at Nata Representative Area
General
The methodology of the measurements is described in Volume 4 Chapter 5.
The soil moisture measurements in Nata basin comprise four stations spread over the investigated northern part of the basin. The latter being very flat and with no expressed sandy hillslopes does not allow compositions as those made in the Tumbi representative area. The amount of stations in Nata also limits the possibilities to draw any extensive conclusions from the soil moisture measurements. However one interesting comparison has been made below.
The soil moisture variations in Nata representative area.
The measurements at Nata began in the middle of December 1978 and were finished at the beginning of May when the WMP project ended.
Hhen comparing the drill ing records from BH 5-314 = 5-413 figure 6.52 and 5-315 = 5-415, Figure 6.55 The following can be noted:
(1) The upper meter is more fine grained at 5-413 with 36% sand against 60% at 5-415.
(2) The portion 1-2 m contains mainly gravel 65% at 5-415 while the corresponding soil at 5-413 consists of clay silty sand.
In Figure 6.56 the water content 'In nm has been shown varying with the depth for the three holes 5-413, 414 and 415. Looking at the upper meter the two holes 5-413 and 5-414, they present about the same moist content. At the depth between 1 and 2 m, however, BH 5-413 shows generally larger values. This means that the water drains off downwards faster in the case of BH 5-415 due to the more coarse grained material, growth, at that particul ar depth. The presence of gravel due probably to the fact that BH 5-415 was drilled in the vicinity of the stream at the center of the valley and the gravelly layer is thus of alluvial origin and not especially thick.
BH 5-414 was drilled up the slope to the east and not very far from the water divide. The soil moisture content shows about the same picture as that of the previous borehole. The presence of coarse material due in this case to the lateritic sand and gravelly layers which, according to the additional investigations, continue to quite large depths. Thus the main infiltration to the deeper laying strata takesplace on the hillsand areas. Judging from the tables in VO,lul'le 4, Chapter 5 the soil moi sture content of BH 5-416 behaves 1 n about the same way as BH 5-413.
-----1978 1979
..............
BH 5-415
BH 5-413
BH 5-414
130
SOIL MOISTURE CONTENT WITH DEPTH
AT NATA REPR. AREA
19/12 26/12 2/1 9/1 16/1 o 10 20 30 40 50 mm 0 10 20 30 40 50 60 mm o ;0 ,20 ~O ~O 50 ~O ?O mm 0 1O?0 (0 40 ~O 8J 70mm 0 10 20, 30 40 50 60 mm 0·0 1 11 ' I! ''7I! ! !
i, i I d h , I
0.5
1.5
1.0
L: __ , L,
'-I ,
r-........ -................ "
L..~~~_
m 25/1 b.g.l0 10 20 30 40 50 mm 0.0 h ' -I ' , ,
0.5
1.0 -, ~.
U 1
L, , -1 ,
J ,
1 __ ~~lj
I-i
1 __ 1
11 I
1--
LJ -----
'1
111
'1 1..., ~
" f.~
1 '--, ,
'--, I
_...J
-.......................... ;
1 1 '--,
I L-, , L, ,
' __ -1 J---- -
'----___ ~L--__ _
-, 1 Ll
1 " _-J.
~~------: 31/1 612 20/2 27/2 7/3 o 10 20 30 40 50 60 mmO _ 10 20 30 40 50 mm 0 10 20 30 40 50 mm
, , I' , I ' ': " , , I ' '11 ' , ,
;1"'1 -1"',
'+, . ..11 _,
LI ----, ,
,r U • ::
,..--I ___ ..l
T····~ ,' .... , 1 : -l=
I: i!····-l , --1
o 10 20 30 40 50 mm 0 10 20 30 40 mrr; I • ~ ! ! , ! 1. ' .1' !
i •••. :
-------- "':
i-----...JI. ......
'----_ I ...... , ~~_ '------_
Fig. 6.56
• ~ ~ ~ .~ ., -I -I -I ~I I I I I I I
I I I I I I
131
2.2.3 Ground Water Conditions in Nata Representative Area
The ground water conditions at Nata differ in some respect from those in Tumbi. The main difference is the presence of artesian and subartesian water in the central part of the valley. See the simplified picture in Figure 6.57 This means that the valley partly must be considered a confined aquifer supplied from water infiltrated upstream and from the sides of the valley close to the water divide. The aquifer responds to precipitation during the wet season with some delay. This fact is e.g. showed by the overflowing of BH 5-109 (125/78) at the beginning of April, see Figure 6.58 while the heavy precipitation was in February and March. BH 5-108 (124/78) situated at the outlet of the valley shows the same picture as seen by the rise in the SW after the heavy precipitation period but delayed up to one month. So does CME hole 5-213 close to the water divide in the eastern central part of the valley. However, this particular borehole reflects water level condition similar to the shallow ground water aquifer in spite of its depth, thus proving that infiltration of the deep ground water takes place up the hillslopes.
The shallow aquifer behaves about in the same way as the one at Tumbi. The fluctuations of the water table are very small in spite of rainfall. There are visible variations of a few decimeters in boreholes 5-315 and 5-316, (see Figure 6.58 ) using the results of the ground water levels from boreholes 5-314, 5-315, 5-316, 5-318 and 5-213 a contour map of the shallow ground water has been drawn (see Figure 6.59). The contour map is valid for the month of April; by that time the area around the outlet point to the north was flooded and the shallow ground water level coincides with the ground level +1151 m a.s.l.
The ground water situation at the outlet point BHs 5-108 (124/78) 5-210 (190/78) and 5-317 is quite interesting. The three boreho1es all reach different depths and all show different ground water levels. See Figure 6.58.
The deep boreho1e 5-108 (124/78) reflects the deep ground water as in BH 5-109 (125/78) presenting the same artesian conditions and fluctuations and the same chemical composition. 5-210 (190/78) and 5-317 show ground water levels aaout 10 m b.g.l. with a difference of one meter between them obviously reflecting pressures heads of different layers of the ground water separated by impermeable or semi permeable layers thus effecting
·a hydraulic disconnection. According to the dr411ing observations there are several coarse grained layers which we consider are more or less separated aquifers. When studying Figure 6. one sees a sudden rise of the ground water level at BH 5-317 sometimes about the 20th of March. This could be a refill of an
~111: '
~I/i:i '
~Iiii ~IT IU",I
I1
11
11,
II,!
I' I' ,
132
aquifer about 10 m b.g.l. Sometimes in the middle of April this water has reached the lower aquifer of BH 5-210 (190)78) implying a 0.6 m rise in the ground water level. Assumed that the increase due to the same percolating water there is a percolating velocity of 34 m in 28 days which means a rate of a 1 ittle more than one meter/day.
The ground water conditions are described by the existence of the a sealing layer effectively separating the surface layers from deeper lying layers. The intervening clayey silty layers leads to very little recharge of the deeper aquifer through layers. Further up the hill a lateritic layer plays a similar role. The recharge of the deep lying aquifer takes place from the edges of the valley where the sealing from intermediate layers is not complete.
, ';,,,';';c;-'-' ,._;0~";.'i_~~;\"_.
LAGERBLANKETT FILM PT 15 FORMAT A4
tl +1170 .+ SIMPLIFIED PICTURE SHOWING THE GROUND-WATER CONDITIONS IN NATA REPR. AREA E
+ 1150
+ 1130
+ 1110
T]
lCl
01
U1 '.:i
... -. , . --.-
j. ... .. ~, .. ·t·· . '. I ' ( . 7 •. a • • • - -. •
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0 400 800 1200 1600
LEGEND: ~ direction of ground water flow
\ \ c1aysy silty mtr.
< percolation in soil D sand evaporation in air
I:: :1 river bed gravelly deposit 1%1 1 ateri te
~ ground water table
~ schist ~~I weathered schist
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5
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516
CONTOUR ground water level in m a sI.
direction of ground water flow
DRAWl NG NO.
6.59 CONTOUR MAP SHALLOW GROUND WATER
APRIL 1979 NATA REPRESENTATIVE AREA ;~ _ ~ DATE
jL-________ L-______________________ ~----------------------------L---------Rl!:t..Iohnsan f~&Ja
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134
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~ -1.. re 5-211
I t 125178 ~ _109.;+; -' ~: . -+ Te 5-109 + _____ = ______ .L __________ ~_+~ -L Gl, 5-109
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+ 1153.5
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+ 1141.5 I I 5-317 7 + 1141,0
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PRECIPITATION AND GROUNDWATER LEVELS IN NATA REPR. AREA
TABORA REGION WATER MASTER PLAN
~ BROKONSULT AB ~ CONSULTING ENGINEERS AND tCONOMISTS
PER SUNDBERGS V t-J $-111.363 TABY SWEDEN
DAfE owe; Nn r; ~ R
136
2.2.4 Comments on the Extracts from the Computed Maps; Nata Representative Area
For comparison with known conditions at Nata representative area extracts from the computed maps of ground water potential, geology structures, land form and land surface are presented. In the following the results will be discussed.
General
Nata representative area is situated about in the middle of the computer extracts. The lxl km blocks which concern the area are marked on the maps. However, as can be seen in all 8 blocks are marked while the basin in reality occupies only about 5 km 2 , which means that the basin only occupies parts of some of the blocks.
Ground Hater Potenti a 1
The computed yield map shows possibilities to extract 3-4 m /h at the outlet of the valley in the north. The two deep boreholes 124/78 and 125/78 produced 2.3 m /h and 4.0 m /h respectively which consequently agrees well with the computed yields. Further to the south there are possibil ities to obtain higher yields, 9-12 m /h. This depends on the presence of the contact zone between the granite to the south and the Nyanzian bedrock types to the north. The structures type lineaments actual to the extracted map has been shown and it might he noted that they imply an about 100% increase of the yields.
Geology
The geology map shows granite to the south, laterite in the middle and alluvium to the north. The distribution of the blocks agree well with the field observations, compare the photos.
Land Form
The land form map coincides well with the geology. The granite blocks to the south are pediment undifferentiated, the laterite blocks in the middle have been mapped peneplane and the two alluvium blocks to the north have become floodplain.
Land Surface
The southern part is occupied by village land and woodland while scrub and grassland are found in the north. Compare the photos.
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137
EXTRACTS FROM THE COMPUTED MAPS GROUNDWATER POTENTIAL, STRUCTURES AND GEOLOGY
NATA REPRESENTATIVE AREA
GROUNDWATER POTENTIAL Legend:
( - ) : 0-1 m /h ( : ) : 1-2 m /h ( > ) : 2-3 m /h ( = ) : 3-4 m /h (+) : 4-5 m /h (X) : 5-7 m /h (M) : 9-12 m /h ( $ ) : 12-16 m /h
2222222222222222222 2222333333333344444 6789012345678901234
*-------------------*
l26 325 324 323 322 3.2 1 320 319 318 317 316 315 314 313 312 311 310 309 308 307 306 305 304 303
2222222222222222222 2222333333333344444 6789012345678901234
*------------~------* 1=======--==>----=--1 I======---==>--->---! !======---===--=---=! 1--============>--->1 I-X=============---=! I-X============>---=I
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1 1 .!. .
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l ! ;; I l i +: +i; I; i 1 + + + +1+ 1 1 1 + + + ! 1 + + +++ 1 I + +++++++ + I 1 + + + 1 I + ++ I 1 + +++1 I + +++++ I r + ++ +I I + +t ++ I 1 + ++ + + ! 1 + + + 1 I ++ +>~ ++1 *-------------------*
STRUCTURES Legend: (+): Li neament (X): Fault
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138
EXTRACTS FROM THE COMPUTED MAPS LANDFORM AND LAND SURFACES; NATA REPRESENTATIVE AREA
LANDFORM
Legend:
(= ) : (X) : ( ! ) : ( & ) : ($) :
Fl oodpl ai n Penepl ai n Plateau Pediment Undiff. Outcrop, No Soi 1
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;>:=~·t&3;~$tt~~~&~~~;~&I I==~~~l~&&&t~:~~~&~~~I !)(~==Gtt;.&~;&(~·&~&~=~r -~·~~t=~~:&@:2.&~~·&a=:~~r :):~x~~=====&t~:~t~.t=&tJ ~ ;.,:; :< >': =::: ::~ :-< :-< j::~. ;:: ;:.,;: :::.: ;':. ::.: ~.: ::..: ;~: I : ::: ..... ; :::: ;:: ; .. ; :-;: :< ;.< >;:~ :::: :.~: L :: :: :;::..~":;:";: I
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LAND SURFACE
Legend:
( ): Vi 11 age (»: Grass (*): Scrub (M): Woodl and (X): Water
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139
CHAPTER 3 GROUND WATER POTENTIAL IN TABORA REGION
In this Chapter the waterbearing capacities of the different geological formations are discussed. The geology and the structural pattern of the region are described in Volume 8. In that chapter the formations are grouped in socalled mapping units which have been coded for the computer treatment. The list of these units is given below:
Code Unit
1 Swamp ) Mbuga clay ) All uvi um )
2 Lacustri ne deposits
3 Deep resi dual Laterite
4 Bukoban
5 Ubendian
6 Nyanzi an
7 Dodoman
8 Gran i te
soi 1
Basic Description
Mapped as one geological unit
(more than 5 m deep) (Laterite soils and murrum with pisolite laterite)
(Mudstone, shale, phyllite, sandstones)
(Marble, quartzite, graphitic schist, chloritic amphibolitic kyanite schists etc.)
(Quartzite, phyllite, conglomerate, sandstone, banded ironstone, mica-schists, acid volcanics etc.)
(Gneiss, schist, etc.) , (Foliated gneissic granite, microgranite, granbdiorite)
The first part of this chapter describes "the deep ground water" i.e. the aquifers in the overburden and the bedrock which preferably can be exploited by drilling boreholes through the waterbearing formation.
The second part is dealing with the socalled shallow ground water. The denomination shallow ground Ivater has been chosen only to describe the aquifers that supply the shallow wells which are dug by hand, the oldest and most common way to artificially catch the surface water, penetrating and percolating in the overburden and in particular the uppermost portion of the overburden.
.. .. .. at
-.. .. " .. .. .. -" " !b ~ ,. --"-:~f ~.
140
It should be stressed upon that the distinction by using the terms shallow and deep is based upon the method of exploitation • Thus the shall ow well s in the region usually have been dug down to 3-5 m and they are sel dam deeper than 8 m. So generally the exploitation of the shallow aquifers is limited to 0-10 m below ground level. However, some of the exploitable shallow parts are deeper and the water supply can be enhanced by drilling shallow boreholes down to 20-25 m in some instances •
The span of the shallow ground water or wells can be 0-20 m and the span of the deep ground water or wells everything below 20 m. The limits depend upon which horizon is giving the greatest amount of water i.e. when drilling a borehole in a valley the water inflow usually increases below 15 m and a common water struck zone is the transition between the overburden and the weathered bedrock which very often is found between 20 and 30 m below ground level •
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141
3.1 Aquiferous Properties of the Hydrogeo10gical Units Relevant to Deep Boreho1es
Unit 1: Mbuga clay, alluvium
The denomination of this unit is a bit strange being a mixture of a material of a particular grain size, and the general term for material transported and deposited by streams. The reason for this classification is that on the geological maps the region is to a great extent covered by the socalled clayey deposits which cover the flat lands and has the Swahili name mbuga. The mbuga i~ usually of alluvial origin and covers in the valleys alluvial silty sandy gravelly deposits i.e. the alluvium in the unit name.
As an aquifer the mbuga (clay, silty sangy clay etc.) is poor the permeability being usually less than 10- m/sec. On the other hand the alluvium (silt, sand~ gravel) exposes permeabilities ranging between 10-8 and 10- 1 m/sec or higher if the material is coarse. The alluvium is usually found in the central part of the valley fill and thus the waterbearing, comparatively porous material can reach thicknesses over 5 m. The thickness of the overlying clayey sediments varies depending upon the local conditions. In wide valleys with a low gradient where the conditions during the sedimentation have usually been calm the thicknesses of the clayey sediments is larger than in narrow valleys with higher gradients. The records of the eXisting boreholes and the record of the WMP boreho1es together with the result of the geophysical investigations have given a statistical estimate for an average figure of the depth of alluvial deposit in the valleys as 30 m. The standa rd devi ati on is 6 m.
Unit 2: Lacustrine Deposits
The 1 acustrine deposits occupy the pa rt northeastern f1 at1 and of the Igunga District. See the geological map in Volume 8. According to earl ier drill ings and some gravel pits these sediments consist from the top of calcareous depOSits, half consolidated si1tstones intercalating with layers of clay here and there silicified. This half consolidated top1ayer has a thickness varying between 10 and 20 m in different locations. In the deeper portions of the f1atland these deposits are covered by black si1ty clay or clayey silt, the socal1ed black cotton soil which sometimes reaches a thickness of 2-3 m and more. Below the calcareous sediments a series of silty cl ay and sandy sediments follows. The latter is probably half consolidated towards the bottom and resting upon the Nyanzian formation.
I
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142
Considering the drilling carried out (there are very few existing boreholes and only two successful WMP ones, 160 and 169/78) show that the formati on usually does not offer sati sfactory aquifers. The water is usually salty and hence the area is considered to be less promising for ground water supply. It should be mentioned that fresh water can be found in the shallow aquifers in the calcareous deposits as for instance at Sakamaliwa but the capacity of these aquifers seems to be small. In the big valleys of Manonga and Wembere the depths to bedrock are more than 100 m but in the plateauland and southwest of these valley the depths do not exceed 100 m.
Unit 3: Deep Residual Soil and Laterites
This group of soils comprise insitu weathered and short transported material which usually is found on higher portions of the valleys and lowlands than the alluvial sediments. To this group the common lateritic formation belongs for instance the socalled hardpan or murrum which is described in the geology chapter in Volume 8.
The two units 1 and 3 can intercalate with each other and it is sometimes difficult to diffferentiate them in the transition zones. A very common lithology is where alluvial sediments cover residual material. Many borehole profiles bear witness of this condition for instance the boreholes in the valleys around Uramba and Tumbi (SH 66/78, 67/78, 68/78 and 106/78). A borehole which possibly exposes a more pure residual soil profile is 181/78 as well as 1/79.
Unit 4: Bukoban
This formation is found in the westermost part of the region. No field investigation has been carried out here because the outcrops and possible borehole sites are located in remote and almost inaccessible areas. According to the photointerpretation the formation occurs as flat plateaus with step slopes outcropping west of the railroad Kaliua-Mpamba. The bedrock is interpreted as a sandstone which probably is quartzitic. Earlier investigations in the same formation in the West Lake Region have shown that the quartzitic horizon can be interlayered by schists and dolerite sills.
The formation has exposed comparatively good waterbearing properties. In the Biharamulo area yiel ds of 5-10 m /hr (1.4 -2.8 x 10-3 m /sec were observed. The values of yields coincide
.. with information given in the publications "Hydrogeology of Tanzania Mainland, East Africa" by W.S. Lyimo, 1977.
143
Unit 5: Ubendian
This formation covers the southwestermost part of the region, that is mainly the vast flatland of the Ugalla river valley. Very few outcrops coul d be found here by the photo interpretati on and the accessability is the same here as for the Bukoban formation. Also for practical reason this area, being a forest and game reserve, could be looked upon as a less preferential subject than the habitated zones. The bedrock is here highly metamorphic and consists of gneisses, schists of different kinds, marble etc. The water potential of this type of bedrock is usually rather low. According to the publicatton mentioned above the yields reach about 2.0 x 10 -3 m 3 /sec. However the i nformati on is based upon rather few examples which seem to originate from the Masasi area in southeastern Tanzania.
The characteristic permeability for this formation with its high variation of bedrock is difficult to calculate but is here estimated to 4.0 x 10 -6 m3/sec.
Uni t 6: Nyanzi an
This formation occupies the northeastern areas of the region. Outcrops and the characteristic reddish soil originating from the weathered bedrock are found from the northwestern part of the Nzega district to the northern and central part of the Igunga district. The banded ironstone which usually is building up the central part of the ridges is not that frequent here as for instance in the Mwanza region. However the higher ridges seem to consist of ironstone' but the lower portions are built up by shales, schists and quartzites. The ironstone is a poor aquifer but the schistose and quartzitic parts of the formation seem to be comparatively promising in this area in combination with the overburden. Thus boreholes in the Nata area and at Nyandekwa have shown that the sedimentary bedrocks offer rather good waterbearing properties. It is possible thilt the obviously rather flat bedding of the laminated part of the series here is favorable for the catching and carrying of the water i.e. building up aquiferous zones along more porous and jointed layers. Naturally weakness zones, faults and joints, which are intersecting the layered bedrock increase the capabilities of the waterbearing bedding planes portions.
Unit 7: Dodoman
The bedrocks belonging to the Dodoman formation are considered to be the oldest in Tanzania and are metamorphic, gneisses and sChists, i.e. old sediments. It covers the central and southern part of the region and the boundary towards the granites is more or less striking from southeast and towards northwest
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144
diagonally over the region. The schistose gneissic bedrock in itself usually is not a very promising aquifer but along weakness zones a borehole can give better yields better than in a granitic area.
The outcome of the boreholes drilled in the gneisses or gneissic granites for instance in Urambo can be considered as good.
Within this series of bedrock the influence of the weathering is important. It is obvious that the frequency of the weathering increases along joints, faults, transition zones between different types of the bedrock and in schistose zones (see also Unit 8: Granite 1 •
Unit 8: Granite
The granitic formation exposes a variation between the granites, i.e. isotropiC masses with no visible parallel orientation of minerals and the gneissic granites, foliated and with bands of oriented minerals. The bedrock mass is dense and has a low permeability. The disposition for cracking of the granitic bedrock is initially depending upon the orientation of the minerals in the isotropic mass which gives the characteristic almost cubic or rectangular joint structure in the outcrops. Due to the releasing of the pressure the structure is more accentuated close to and at the ground surface. The tectonic movements enhance the initial ·cracks· forming faultzones and jointzones.
The joint- and faultzones are as always exposed to the weathering agencies which to a certain extent increases the possibility of promising aquifers. The weathering of granite and granitic bedrock in a certain phase creates clay minerals which can seal the porous zones in the bedrock. However, it is clear that the weathered parts and the jOintzones in the bedrock are creating the aquifers. The values of yields and permeability in this report thus refer to jointed and weathered bedrock.
It shoulti be mentioned here that the dolerites have' not been looked upon as a separate unit. The permeability of the fresh dense dolerite is almost same as or lower than the one of the granite. The weaterbearing zones in the dolerites are the jointzones and the contact zone with country rock such as granites is usually in itself a poor aquifer. This result is characteristic for all dolerite dykes found in this part of Tanzania. Thus similar conditions were found in the Mwanza Region. However, the grani te close to the dol erite sometimes seems to have been affected by the dyke intrusion which has resul ted in an increased joint frequency as well as deposition towards weathering. Possibility to drill inclined boreholes should enhance the probabil ity to find the waterbearing zones at the dolerite dykes.
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145
3.2 Control of Ground Water Levels
In order to investigate the variation of the groundwater level in different parts in the region some boreholes were controlled from the beginning of the field work in May 1978 and to the end of the project in March 1979.
The control began with an existing borehole in Urambo District No. 3/69 and continued with the WMP boreholes as they were drilled starting with BH 66/78 in Uramba Village, Tabora District. The following list shows the boreholes and the type of bedrock and overburden in each case,see table 6.7. '
It should be mentioned that in the description of the representtative areas, Chapter 2. the ground water situation within these areas is discussed in detail.
146
TABLE 6.7 GROUND WATER LEVELS IN TABORA REGION; CONTROLLED BOREHOLES.
BH No. Overburden Bedrock Water Struck Remarks
66/78 Gravel Sand and si 1 t W. Granite 21.0 0.0-42.4 m 42.4-50.3 m
67/78 Gravel Sand and si 1 t W. Granite 21.0 0.0-34.8 m 34.8-44.8 m
68/78 Cl ay sand W. Granite 22.6, 30.2 and sslt 0.0-27.1 m 27.1-34.2 m
105/78 Clay and silt W. Granite Water level 0.0-2.7 m 2.7-11.9 in the hol e
Fresh granite at 30-31 m 11.9-90.5
106/78 Clay, silt W. Granite 21.0 gravel 21.0-34.2 0.0-21.0 Fresh granite
34.2-58.8
124/78 Clay, silt Sil tstone 39.3 sand gravel 10.4-36.3 0.0-10.4 Shale
36.3-44.8
125/78 Clay, silt Silt- 16.5, 41.8 0.0-21. 0 sil tstone
21.0-24.1 Shale and schist 24.1-44.8
137/78 Lateri te W. granite Water level sil t and sand 2.7-17.4 in the hole 0.0-2.7 Fresh grani te at 24.9-25.4
<'3.5-90.5
144/78 Laterite W. grani te 43.3, 54.6, 57.6 silt and sand 11.3-12.8 0.0-4.3 Fresh grani te
12.8-57.00 W. grani te 57.0-60.1
7/78 No record No record Water level probab 1y gnei ss in the hole
0.2-0.9 m.
3/69 No record W. granite Water level 0.6-46.97 46.97-55.20 in the hole
Gneiss and 0.51-3.2 m. granite 55.20-80.2
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The results are recorded in diagrams. See Fig. 6.60, 6.61, 6.62, 6.63.
Following comments on the results can be made:
For the boreholes 66/78 and 67/78, where the aquifer is located mainly in the overburden and the upper weathered part of the granitic bedrock, the water level in all follows the yearly variation of the precipitation. After May the level in 66/78 is sinking about 0.5 m and the level is fairly constant to the end of November after the rains have started. Then the level is rising again about 0.5-0.8 m during December and remains at that level during the wet season. BH 67/78 shows the same picture but the increase after November is much more accentuated the level going up from about 4 m to 0.5 m below top casing in December.
Boreho1e 68/78 is showing the same variation but the rythm is slower as the water level is going down in June and then rises slowly in February •. The delayed reaction depends upon that the aquifer mainly is located to the jointed bedrock.
This condition is more accentuated in the borehole 105/78 where the water infl ow is low and enti rely recorded in the bedrock. The water movements are small varying between 0.4-0.5 m and the level is not sinking until August and is slowly rising again during December-January. In boreho1e 106/78 where the control did not start before August, the level was rising from 14 m to 13 m from August to September and was then almost constant during the rest of the field period. The downward peak in November is probably an error in the measurement. As the water level is almost constant during the rainy season the waterbearing conditions seem to be slow but stable.
The two boreho1es 137/78 and 144/78, also drilled in granitic bedrock and with the inflow recorded only in the bedrock, indicate similar conditions as were found in for instance the borehole 105/78. The reaction of the precipitation is very slow as the water level is going down both in the boreho1es only during November and is then very stabl e for the rest of the peri od. The boreho1es 7/78 and 3/69 which both are drilled in granitic and gneissic areas as well show a delayed reaction on the precipitation. However it seems to be faster in 3/69 than in 7/78 as the level is sinking after May from 0.5 m down to about 3 m in October and is then constant to February when it is moving upwards again. The measuring period is shorter in BH 7/78 but is showing the same tendency but with smaller variation.
Unfortunately there is only one boreho1e recorded in the Nyanzian formation No. 124/78 at Nata. The tendency is here that the water level reacts rather quickly after the dry period as it is rising from 4 m in September to 1 m in November andi s very stable for the rest of the ra i ny peri ods. It shou1 d be menti oned that the boreho 1 e 125/78 exposed almost artesian conditions the water level being at the ground level or sl ight1y above the ground level (in the casing) throughout the period.
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9,0
148
CONTROL OF GROUNDWATER WARIATIONS IN DEEP
BOREHOLES IN TABORA REGION DURING 1978-1979
a.> c
'" 'J
~
"'\
f\. .-
-
.....-
0-a.>
</)
-
. ..., u
o
. > o z
./
. u a.>
Cl
/ V
-
-
C ..0
'" a.> 'J . L<..
'"
--FIGURE 6.60
~on19S~3
-
-
I; '. .1'
::l !;(
" '" 0 ~
~ ~ n.
" J
u: I: w
" z :I '" '" w
" 5
m. b. T.e. 30 ,0
BH 105/78
31 ,0
13, 0 BH 106/78
14, 0
n , BH 124/78
,0-2,
n v 3,
4, n
149
CONTROL OF GROUNDWATER WARIATIONS IN DEEP
BORE HOLES IN TABORA REGION DURING 1978-1979
'----_. -~---- ---
----
-........
0-QJ
V>
r---..
/ /
. _----
. ..., > u 0
C) z:
\ \ V
I1 I -/
1----
/ _ ... _--
/ '.>
/
. U QJ
Cl
--
/ /
. c
'" ...,
r-
- 1--.
... _.-
FIGURE 6.61
198<3
. .c QJ
lL.
_.-
-I
~ 1
~ 1
~I
I I
BH 125/78
BH 137/78
BH 144/78
BH 7/78
m. b. T.C. o
1 , 0
24,0
25,0
25, n
26, n
o
1 ,0
I 150
CONTROL OF GROUNDWATER ~/ARIATIONS IN DEEP
BOREHOLES IN TABORA REGION DURING 1978-1979
>
QJ C ::l ...,
0-Q)
Vl
. +' U o
-
. > o z:
1
'"
u Q)
Cl
rv /
/
. ..Cl
<f
i-
V
FIGURE 6.62
~~==~-------------------------r----------------------------------~ "*«tfwtson 7 se. 3
~r ~II ~II: -Ill '.Ifi ' ~IIII &hl~ :
hili' ~l~ ! l},!1 ' It I,; i
~!
Ill! '
Ilil: ;
III !
m. b. T.e. D
BH 3/69
1 ,0
2,0
3,0
151
CONTROL OF GROUNDHATER WARIATIONS IN DEEP
BOREHOLES IN TABORA REG.ION DURING 1978-1979
"-'" ~
~
FIGURE 6.63
. ..... . 0. ...., QJ U
(/) Cl
~
. > o z
. U ID Cl
. s::: '" ....,
. .Cl ID
lL.
I
I
I1 V
152
.Conc1 usi on
The investigations have shown that the aquifers in the region with few exceptions are complex and that the .Yields are the result of the combined waterbearing properties of the overburden and the bedrock. Thus the grouping of the aquifers resu1 te-d finally in only three big units of aquifers: Deep residual soil s, -alluvial soil sand structures.
The two overburden units include the UP~r weathered portion of the bedrock whi ch is looked upon as a transiti on zone hard to define as overburden or bedrock.
The aquiferous properties of the bedrock are determined by the frequency of joints and faults.
The frequency of 1 ayered bedrock which can offer aquiferous porous laminated horizons is not that high in the region so it can affect the dominance of the structures as enhancement of aquifers in the bedrock. The two overburden units are here called the main aquifer. The characteristic of the units is given in the following table. 6.8.
It is cl ear that the 1 ake sediments and t.he Nyanzi an "core bedrock", the banded ironstone, are poor aquifers Considering both the frequency of waterbearing zones and as for the Lake sediment, the water qual ity. The structures, joints and faults creating valleys - catchment areas increase always the aquiferous properties. Thus, the low frequency of structures in the northeastern part as well as in the southern-southwestern part of the region makes it d,ifficult to define and survey the aquifers in these parts of the region. However the interpretation of the airborne geophysics can offer an opportunity to solve the problem at least in the southern and southwestern part of the region.
TABLE 6.8.
AQUIFER PROPERTIES OF INVESTIGATED GEOLOGICAL UNITS IN TABORA REGION.
AVerage Stand-ard Average Standard Average Average Geology Class Land Cl ass Depth to Devi ati on Water Deviation Permeabil ity Q 3
Bedrock (H) Struck (so) (M/Sec) (M=-/sec)
Deep resi dual Deep soils 28 m 6.5 4.5 2.5 2 x 10-5 2 x 10-3 soil
Alluvium Alluvial 30 m 5.5 4.0 1.5 8 x 10-6 2 x 10-3 deeosits
Structure . Structure 48.0 19.0 1 x 10-5 1.5 x 10-3 U1 w
~%'i!,;;!;;;'!i4%ff:'~"-'" 3 < ";iII
~ ~it -. -. --. -1 ~,
r~:1
>1
1 ~ t t , t ~
if '~ ;. r~~'~
~t _ _ ,.k
3.3
154
Deep Ground Water Potential Estimates
The calculations made for the determination of the groundwater potential are based on informations gathered from the existing boreholes, WMP boreholes, geophysical investigation geological and landform surveys and finally the estimations of recharge within the different climatic zones.
Basic Calculation, Deep Ground Water
The problem that must be solved is how to estimate the yields to be expected from well sited boreholes. This is an extremely difficult question and the answer we provide here should be considered a first approximation. As ground water is exploited in the region the basis for these estimates can be improved. We have sought to establish a connection between the yield and the basic hydrogeological conditions which would permit estimates of the yields. The usual approach to these estimates involves identification of the type of aquifer and then links the hydrogeological conditions to the yield in a manner dependent upon this aquifer type.
If one uses a confined aquifer then the steady state yield equations require specification of the radius of influence of the well. There seemed to be no useful way to estimate this. Furthermore, in the conditions typical of Tabora where one is dealing with aquifers in rocky conditions the water available for pumping is precipitated in the vicinity of a borehole. As we know something about this recharge potential of the ground water it was decided that we should consider the aquifer 'as unconfined over a long period.
Thus to establish a yield equation we assume a steady state, isotropic, fully penetrating well, recharge, non-confined aquifer. Essentially this means we calculate how much water can be extracted indefinitely from the aquifer i.e. without "mining". The rainfall?n any particular year may be high or low while the extraction rate from the borehole is constant; thus the ground water reservoir serves to smooth out the difference between recharge and extraction. We take the aquifer to be unconfined as the best approximation to the actual conditions. If a more or less confined aquifer prevails the sealing layer is given such a low permeability that it does not effect the calculations but still allows us to use the equation val id for unconfined conditions. We, are averaging over the year, there is always 'downward movement of the water and the ground water reservoirs are presumably full, so the unconfined aquifer with recharge is a plausible approximation. To understand this argument, we reiterate that the well behavior is meant to be averaged over long periods. The areas considered are typically one square kilometer so we believe we are usually including the recharge area even when the ground immediately around the borehole is impermeable.
I
I i
'I I
155
On these assumptions the relevant equation is:
=
where:
Ji. (r2 _ 2K w
o is the extraction rate
W is the potential ground water recharge (m/sec)
K is the permeability
r is the radius of the borehole w
r is radius of the zone of influence o
H
s o
is the depth from the surface to the sol id bedrock.
is the depth from the surface to the static water 1 evel •
h is water level in well measured from the bottom of the w well.
See Figure 6.64. for the notation. Also we have the relationship relating extraction, recharge, and radius of i nf1 uence.
"- 2 "·r o
W = o i.e. recharge equals extraction.
In effect this eleminates the unknown ro'
To obtain the maximum extraction we want to obtain the maximum practical drawndown. This maximum drawdown allowed is defined by the depth of the borehole (H) with an allowance for the pump and for head loss due to turbulence. For H given, we can determine the maximum drawdown as a function of O.
= 2
3 + CO ~
We estimate C from the drawndown tests. The 3 meters is the pump turbulence. In the drawdown equation we use the above to eliminate hand r and obtain: w 0
156
1 1 1 1 i+ t-rw , , , , "~,,
M "~"""~,, "",.""" d" H< '"= '''] ::::~.&; :;::-F. ::rr~/. :/(0:::"':"/_ ::::-1'/.:1'=//.::: 1'~//_'r=I'/_ /1:::
H
So
SIiI, ro ." --- I- .
-
hw
FIGURE 6.64 Steady flow to a well penetrating an uniformly recharged unconfined aquifer.
i'
[
For a given
For the area ground water 1 ogi ca 1, and
157
JL In 7fK
aquifer we specify H, s, K. o
for which we are making the estimate the potential recharge is known from the precipitation, climato-1 and use data. (See Vol ume 4.)
Then the above equation is solved for Q, the extraction rate. This is the basic calculation done for each geology class (i.e. aquifer type) in each square kilometer block in the region.
=
We now proceed to estimate th parameters H, s , and K under different conditions, investigate the sensitiijity of the equation to various parameter changes and then compare the actual test results with the computed results. We have analyzed the data to obtain an overall consistency of results. Then we have used the results of the parameter estimates to determine the potential yields in every square kilometer of the region.
SpeCification of H
It should be kept in mind that H is the sum of the thickness of the aquifer and the distance from the ground to the static water level. Apart from existing boreholes and WMP boreholes (see below), data from geophysical profiles, especially the long profile program Volume 7, Section 3.5 have been used. In this way it has been pos$ible. to estimate a value for all eight geology cl asses. Th~ estimated H = "Depth of Overburden" for each of the geology classes is shown in Table 6.9.
Irregularities of the bedrock, i.e. structures will increase H considerably with major effects on the ground water potential. The structures have been divided into two groups:
A. Lineaments: Comprising jointzones, weakness zones and contact zones between different kinds of bedrock. These features can be
"recognized on air photos but are often difficult to distinguish from each other. They imply often a magnetic anomaly and increased thickness of weathered bedrock in the central part of a valley or in the close vicinity of it. Drilling for water in these zones means increased yields in most cases. When lineaments are present H have been doubled.
o
~~"~ .•.. ~ . . :~? '4
f
i f i 1 I f t f f
.. ~
B.
158
Faults: These features comprise a movement of one part of the bedrock in relation to another causing a displacement in more or less vertical direction. The movements cause cracking and decomposition of the bedrock which imply enhanced weathering in those zones. Faultlines are in general quite extensive and can be followed several kilometers through the landscape. They often have a damming and draining effect on the ground water which makes them in general good aquifers. However the position of the faultlines in the landscape implies often that the groundwater levels are found comparatively deep. When faults are present the value of H are increased two or four times depending on the geology class see Table 6.9.
Specification of K
Permeability (K) estimates are obtained from the well test data. The well test gives an estimate of the transmissivity. Also transmissivity is equal to k x thickness of aquifer (HB - S or H-S ) (it can be noted that the upper limit S of the 0 aquifeP sometimes is equal to the static water 19vel). If there is no structure the thickness is equal to the depth to bedrock which sometimes includes the uppermost weathered part of the bedrock. If there is a structure the total transmissivity of the borehole is considered as follows i.e. transmissivity of the aquiferous overburden - weathered zone + transmissivity of the structure zone +transmissivity of the remaining nonaquiferous part of the borehole.
The permeability values obtained from the well tests were compared with the total sum of the permeabilities of the different aquiferous layers as they are given in the basic information above. The permeability values are here collected partly from reference literature (column 1l partly from well test results (column 2).
Col umn 1 Col umn 2 m/sec m/sec
Dl clay -10 -10 K = 10 10
D2 si lty cl ay 1 -8 -8 K = 10 10
D3 silt 2 -7 -8 K = 10 10
D4 si lty sand 3 -6 -6 K = 10 10
DS sand fine 4 -5 -4 K = 10 10
D6 sand 5 -4 -4 cOOrse K = 10 10
D 7 gravel 6 -3 -4 K = 10 10
D8 weathered 7 -6 zone K = 10
Z structure 8 -6 zone Z = 10
"
~ill i
iil.
/1 .,
;i
!
! I
!iJ: .. I,
159
Total permeability for an aquifer consisting of n layers without structures:
=
with structures:
=
1 fj:$-
z
o
H-s o
n
L D x K 1 n n
K + o
n
1 LK H-S 1 n
o
x D n
Thus for the lithology of a borehole we are able to compute the estimated permeability by averaging the layering.
Specifications of So
The estimation of static water levels have been based upon data from representative areas,existing-and WMP boreholes. To some extent contribution has been obtained from geophysical profiles. The static water level for each geology class has been estimated to between 4 and 9 m. The last depth is thought being valid for 1acustrine areas. The presence of faults means a lower ground water table because of the fact that the comparatively coarse material which appears in connection with this feature is situated fairly high when comparing the surroundings.
In the drawdown equation it is the difference H-s that matters. As s is usually small compared to H a 9arge error in So has rela~ively little impact on the estimated yield.
Specifications of W
The potenti al in Volume 4. land use.
ground water recharge is calculated as described It is a function of climate zone, land form, and
The meaning of the potential ground water recharge is that it is the volume of water which would go down to the ground water reservoir if there was room for it! If the reservoir is full then the water cannot percolate and will appear as run off. However, as ground water exploitation continues and the amount of water increases then one makes room for increased recharge. That is why we call this estimate the potential recharge. However, this means that the actual recharge is variablft accordin·g to the amount of pumping. For calculation pul'poses it is correct to use the potential ground water recharge as this defines the water actually available.
A.
B.
160
The parameters ro and C
There are two remaining parameters necessarily to solve the well equation. Those are the following constants:
The radius of the well r o
r = 0.075 (m) (radius of 6" casing)
The well loss constant:
c = 3.5 x 106 2 5 (sec /m )
Thi s val ue is an average fi gure obtained from the well test calculations.
In Table 6.10. we give the parameters for the three cases of: no structure, lineaments, and faults. The~ using these . parameters we have calculated the yield (m /hr) for the eight geology classes for two characteristic recharge rates 50 mm and 200 mm. This table indicates the range of yields we believe can be achieved in Tabora in different aquifer conditions. Examination of this table shows clearly the importance of drilling on faults or lineaments if these c3n be located. Yields without structu§es are less than 5 m /hr (this corresponds to 50-60 m /day). Typically yields increase 2-3 times if the borehole can be sited properly. This indicates why it is worthwhile to invest substantial resources in the careful siting of boreholes using geophysical and remote sensing. This table also indicates the very poor ground water prospects in the lacustrine deposits which from these estimates have very little prospect to yield usable volumes of ground water.
IIIl" ....... is -= ~~:--=-..,
OJ3
!!i!!!" """'" ....".. -----,.
'J;
Geology Cl ass
~ ~. 1. Alluvium, mbuga ~'::l -h~ swamp rD'< -,
V> o 2. Lacustrine deposits ~.
~
- I 3. Deep soi 1, 1 aterite
4. Bukoban formation
5. Ubendian formation
6. Nyanzian formati on
7. Oodoman gneiss
8. Granite undiff. .,
'" I
ta,Y;<ii'. .-.~~ . .;~::::::- -~~ ~~ ~ r::::r- ,;;;~ ~i~ 1!!!F =!!! ,&.£j .~ . J&? .. ;;;;;;; c.!!' J
'-;-. -.--:~''''-'~
;::: -:::-.::-::---.... -. -.-~',--' .. ----~- --'-<,..,.,.,...,..~-.---,--. -·----·----=-_ .•. _, .. -,-O' ____ ."7:":'"T_ __~_:_-
TABLE 6.9. TABLE OF PARAMETERS FOR ESTIMATING DEEP GROUND WATER POTENTIAL
Depth of Permeabl- Lineaments Faults SWL Overburden 1 ity SWL Depth of Over- Permeabi- :'WL uep"tn or uver- permeaOl-(m) (m) (m/s) (m) burden (m) lity m/s (m) burden (m) lity m/s
4 22 8 x 10-6 4 44 !>.9 x 10- 5 10 80 8.4 x 10- 5
9 40 1 X 10- 10 9 80 5.7 X 10-9 9 80 5.7 x lO- 9
4.5 18.5 2 x 10- 5 4.5 37 4.9 x 10-5 10 80 9.0 x 10- 5.
6 15 3 x 10-4 6 30 1.8 X 10-4 6 30 1.8 x 10-4
6 30 4 X 10-6 6 60 5.7 X 10-5 6 60 5.7 x 10-5 0)
7 45 1 x 10- 8 7 90 5.5 X 10-7 6 90 5.5 x 10-7
4 20 1 X 10- 5 4 40 7.4 X 10-5 10 80 8.7 x 10- 5
4 23 1 x 10- 5 4 46 5.9 x 10-5 10 80 8.3 x 10- 5
162
Evaluation of Parameters of the Well Equation
As the well equation is quite complicated an evaluation of the different factors has been carried out. The most interesting one is undoubtedly the yield Q and in the following Q the effect of changes in the different factors belonging to the formula has been investigated. The parameters have been allowed to vary within reasonable limits.
A. Yield vs Permeability and Structures
The study has been carried out with parameters belonging to geology Cl ass 7 and the results plotted in Fi gure 6.6'5.
An interesting fact is that the yield increases from greater permeabiliti~s only up to a particular limit. That limit is about at 10 m/s, slightly higher in the case of "without structure" • Note that no _~nhancement of the yi el ds are obtained at permeabilities over 10 m/so The permeabilities used for the regional yield-map are specially marked on each curve.
T~e presence of structure increases the yield substantially. Presence of a lineament means an increase of about 50% at high permeabilities and still more at lower. A fault increases the yield more than 100% at high permeability and as much as 10 times at lower permeabi1ities. This effect depends largely on the increased H value. Variations of the static water level s affect the yield very little. o
These results indicate that the choice of permeability for structures is robust and yields will not change for errors of a factor of 10. For the non-structure case the yields are more sensitive to this assumptions. A factor of 2 in the permeability will change the yield by 30%.
B. Yield at Varying Recharge W
In order to check the effect on different recharge yields were calculated at the recharges of 50 mm/y and 200 mm/y. The effect of this manipulation is shown in Table 6.10. It is obvious that differences in recharge have little or no influence on the yield. Small differences are found at cases of low yield and no structures where an increase of about 10% was obtained in a few cases. Consequently, we conclude that the yield estimates are robust with respect to the, potenti a1 recharge.
C. Yield vs Well-Diameter
The relationship between yield and well diameter was studied in geology class 2 lacustrine area at the case of no structures. The following result was obtained.
N3/H
10
"0 ~
Q)
>-
1:0 "
0.1
~L.
.. '--6'--"'~ , 1 0 ' ' . ....+.---+
" . -] -
.. ~~IFt·i~':r. i-··n~~.;.msI~;g~JI' ~~:~t~;:; " i I !,Ii' ',·F"",·."i'l"., .. ,.I, I. . I •••. H~;t.., '.,
.-< •• ,
i: , . ..., -iTEr I '.' ~ l~INi[~~~Ntt : ':1 . . 1 :. j ; i ! I ! " I .. :' ,,! I" ,.
1_ ,.0 "h ,> ,:, ~~E:::::j-=:.a--"Tt1 +: J ~F=~~,:lP~7W, ", ~~ ,~' ""i' .":;;' . I· .. ·, .. j:::: '~I" : -fA I , .. " .1., .. 1. .. LL:::j!:
·-:-:::-:--·-~-:-:-~·~-~~~'r.-·· ·:-ll-~-b,t:·~~'·-----·-;-:··-:·-·L;::j:':*:-:: ::.':~. ~ : d.~ "" ... , .... ".1 . .,.1 ..•. ,! i .!,nl··--j·"i, +-r'T:~:'iT '+~I:;i:1 ~J:lj]i:;iii .. ,,,,' i,. "1'1 " <",l--,,·,.I,;,}, iJ- 'j' ,·1 '1ff!i+H+!-'Sf:+;
_!mr i :h+r'++~i~T=ijf ; 11 i Ilj'Ti1!lL ".,cuc" ,,'f 'j!
: i~::I~1 chosen::K:~hl~e-;plll-t +'i'I:l !', ,I -11:i1[ I ! .
'·:~'~l::~LLF\.. _.:,).,L:~)·~j ~ :!i I 't', ~- i " -:: ':·f-:-'-L:-°·:++1l'!~J :~.:='L'i.::j:::==fu·' ~ -+!'
ut· ., :r·+~:;:·;(:~.uJ.:~~~~~.+~ ::._-'-C;;:: Ll,:"
·"tT; :'-FIGiJRE:&.651 4 ',++1++
rJHjdl::~'-':-::1 ,:., , , ' I '
.~ _. ____ 1_.--': _--i _ . _'._~ ~_#.! ,~ I ':' ., I I
f·1 'I i i' 1 ' , : 1: :. :: L 1 ,-! i j T! ' ! ,f 1 i ,! I I if.
'\ : ... (I I • I I" : \ - -I - ~ , :. . ,., i . I i . 11 I': . I"""
... ::-5"- --+--;----+--t----+4". ,I 4 I 10 10'
.J ._.
, ._; .• .l ._L--+ ___ _
-; -
'L~I :;,
-·:~.::·~~i;,,'~ljlt;-. ut-t, t· , . 1 ' I • ,
~:::.m:n.r~· ,,' ::+:;cJ=-IP:~I r-'-;---'
: i'
.l
: i
10'3 Njsec ._."... ..... .t€,rmeilbi 1 i ty
~:
! .. ;l .1. ,:
-+
1. -r F
.... -i .
.--!- .)
.L
~
., I
"
(J)
w
Geology Class
1. Alluvium
2. Lacustrine Deposits
3. Deep Soil, Laterite
4. Bukoban
5. Ubendi an
6. Nyanzi an
7, Dodoman gneiss
8. Granite u'ndlff. - -- ----
•
TAr 6, -
YIELDS AT VARYING RECHARGES
DEEP GROUND WATER
YIELD - RECHARGE (m 3/hr) (mm)
Without Structure Lineament Faults 50 mm 200 mm 50 mm ZUU mm bU mm ~Ou mm
3.6 4.0 11.4 11.4 15.6 15.6
3.1 10'4 3.6 10'4 5.3xlO-2 5.9 10-2 5.3xlO-2 5.9 10"
4.0 4.1 10.0 10.0 15.7 15.7
4.5 4.5 7.7 8.7 7.7 8.7
3.2 3.5 13.5 13.6 13.5 13.6
2.8 10"2 3.210-, 5.1 5.6 5.2 5.7
3 1 I 3.3 10.8 10.8 15.7 15.7
4.1 __ 4.4 11. 7 11.8 15.6 15.7 --- -- -- --- ---_._--
2
0'\
""
I I' . il~:" , i .;'1'
11 . , . ,'I I ,.
I· I .
I .1
165
3.7x10-4
3.5x10-4
3.3x10-4
3.1X10-4
6" 8" 10" 12" Well diameter
Fig.6.66. Yield vs. Well Diameter.
The relationship is linear and an increase in well-diameter does not improve the yield to any greater extent. This particular geology case was investigated to determine if it was possible to increase yields significantly by larger diameter boreholes - the answer is that it helps but not enough to make the ground water prospects interesting.
D. Yield vs Well-Loss-Factor C
In order to see the effect of different well-loss-factors on the yield the former was allowed to vary within limits which were collected from earlier conducted well tests at the Tri-Region WMP. The following results were achieved.
C(s2;m5) Yield (m3;h)
5 x 105 6
1 x 106 5 x 10
The values were calculated with the geology Class 2, no structures, and calculation shows that changes in C the yields.
3 1 10-4
• x -4 3.1 x 10_4 3.1 x 10
other parameters from a recharge of 50 mm. The has little or no effect on
166
D. Yield vs Pumping head
Varying the pumping head gives the following result:
PH Cm) Yield ~/h 1.0 3.3 2.0 3.2 3.0 3.1 4.0 3.0 5.0 2.9
The calculations were carried out by means of parameters in geology Class 7 at a recharge of 50 mm/y •. The result shows a slow decrease of the yield. Experience has shown that a convenient and safe pump head is 3 m.
Conclusions
The evaluation of the well equation at which different parameters have been allowed to vary one or a few together at a time the following can be stated: the recharge W, the well diameter 2r , the well-loss-factor C and the static water level s ha~e little or no effect on the yield. The pumping headoPH should be kept at 3 m for saf~5Y reasons. The permeability have importance at low values_~ 10 m/s but practically no influence at values> 10 m/so The most important parameter is H which at reasonable positions of static water level s determines the aquifer thickness. 0
IIIt'II'! ' 1., "
Illi'l
Ill: '
'I~ I It! III
11
I
167
Control of the Computed Yield Map with Data from Existing Boreholes
In order to check that the computed map is relevant to known conditions, those blocks which contain existing boreholes with data on the yields have been extracted from the computed map and shown in the attached list. Only those borehole have been used that carried information on the yields at least by means of an airlift-test. Those yields have been compared to those,yields obtained by estimating the permeabilities from the lithology and calculated by means of all known parameters for a particular borehol e whi ch appear in the well equati on. Fi gure 6:67 shows the relationship between the two yie'lds obtained in this manner. One sees that the values are fairly well assembled around the line indicating 100% agreement. Column ° in Table 6.11 are the yields derived from the computed map. YThe relationship between the computed yield Q and O? is shown in Diagram 6.68 ,between ° and 01 anciY03 (sp!!cially marked) is shown in Di agram y 6.'169.
Comments to the Relationships
Look i ng at the Di agrams Fi g. 6.68-69 one sees tha t many values are quite spread out and apart from the ideal line. Those of the values which are mostly apart from the line are either high-yielding boreholes situated within a block where the computed map shows low yield and vice versa. In all those cases there are structures involved. In the first
case the drilling has hit a structure which does not show on the earth's surface implying that they are not mapped. Note that in most of these cases there is an adjacent structure block carrying a yield comparative to the borehole. The opposite case when the computed map indicates high yield and the borehole performs a poor yield the structure might have been missed. In the following section where the computed yield map is commented district by district the drillings versus the computed yields are further discussed.
However, in general the above results indicate a good result using the yield equation when the lithology of the borehole is known following the drilling. Agreement between computed map and existing boreholes is fair to good. If we include the 3 x 3 kilometer block formed by taking the adjacent blocks into account then we find the correspondence quite good. In our view thi s accurately refl ects the accuracy of our abil ity to pl ace structure locations on the computer map.
· AB LL 0. 11 . YIELDS OF EXISTING BH AND WMP-BH
o 1 02 03 Q 4 BH No. UTM Map Coord. Airlift Calc.Litho. Well Test Computed Remarks
42/79 5522 95323 272.2 302.3 10.4 5.8 15.7 Fault I9 10.8
15/79 5524 95324 272.4 302.4 0.9 2.0 15.7 Structure I9
10/79 5258 95345 245.8 304.5 4.7 0.6 11.4 " I9 Safe yi el d
1/79 5483 95126 268.3 304.5 13.0 14.4 6.8 11.3 .. I9
147/78 5613 95301 281.3 300.1 2.0 2.3 0.063 I9
111/70 5387 95554 258.7 325.4 6.2 5.0 3.1 I9 ~
125/78 5152 95489 235.3 318.9 6.8 4.0 3 Nz '" 00
124/78 5153 95491 235.3 319.1 2.3 1.9 3 Nz
267/76 5258 94742 245.8 244.2 14.7 14.7 4.3 Structure Nz
62/72 5094 95 522 229.4 322.2 2.7 4.0 4.0 Nz
23/60 4860 95338 206.0 303.8 3.2 3.6 3.0 Nz
143/76 3490 94550 69.0 225.0 6.8 6.5 3.8 Ur
12/76 3970 94400 117.0 210.0 3.4 5.4 10.0 Structure Ur
130/75 3482 94545 68.2 224.5 4.5 6.8 3.9 Ur
70/74 3874 95045 107.4 274.5 11.4 12.6 3.9 Structure Ur
48/73 3458 94 570 65.8 227.0 5.3 7.6 3.9 Structure Ur
:~,:X;,t ,_.:;);"~".' ". - "~~;';;' •. ~-.
'-'--'"
Yields of Existing BH and WMP-BH (Cont'd) 01 02 03 04
BH No. UTM Map Coord. Ai rl ift Calc.Litho. Well Test Computed Remarks
47/73 3455 94 540 65.5 224.0 5.7 7.6 3.9 Structure Ur
3/69 3940 94280 114.0 198.0 4.7 4.5 3.1 Structure Ur
8/67 3665 94408 86.5 210.8 12.1 8.1 4.0 Ur
5/66 3668 94410 86.8 211.0 10.0 11.8 4.0 Ur
BH 69 3935 95030 113.5 273.0 6.5 6.8 3.9 Structure Ur
BH 42 4065 95025 126.5 272.5 2.3 2.8 3.9 Ur
BH 40 4115 94990
131.5 269.0 1.2 2.8 3.8 Ur
106/78 4675 94402 187.5. 210.2 1.1 1.2 4.2 Tb
68/78 4701 94400 190.1 210.0 0.7 0.7 4.2 Tb 0'> <.0
66/78 4740 94472 194.0 217.2 1.1 4.3 1.2 2.0 Tb
1/77 4970 94570 217.0 227.0 5.7 6.1 2.7 4.3 Structure Tb
60/75 4652 94388 185.2 208.8 0.9 0.9 3.8 Tb
238/74 4649 94392 184.9 209.2 1.1 1.2 4.2 Structure Tb
119/72 \65 94397
186.5 209.7 2.6 3.2 4.3 Tb
32/66 4250 94355 145.0 205.5 13.5 9.9 3.0 Structure Tb
3/67 3670 94410 . 87.0 211.0 2.3 4.0 Ur
1) Close to 10 m;/h yield 2) Close 0.063 m /h yield
------- ~"."
,---,--. ,---.. ~
Ql M3jH
170
15-r ________________ +-________________ ~--------------~~
+' 4-.~
•
•
lO~--------------~~--------------~~----r----------+-
<: 5 -r--------------~~--------------+----------------+-•
• •
•
5 10
Q from lithology
FIGURE 6.67 Diagram showing the relationship between Ql and Q2(see the text).
Q2 M3/H
171
15.~ ________________ 4-________________ +-________________ ~ • •
• •
101-________ ~~----+_----------------~--------------~-•
~ en 0
,--0
0= +> 5 ,--
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CY
~
•
• • • • • •
• .. ..
••
5 Computed Q
•
•
10
FIGURE 6.68 Diagram showing the relationship between Qy and Q2 (see the text).
•
•
Ql /Q 3 M3/H
172
154-______________ ~---------------4---------------7f-
• • • BH 1/79.
• •
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BH 66/78 same e •• '.
5
Computed Q
®BH 1/79
• value)
10
FIGURE 6.69 Diagram showing the relationship between Qy and Q]/Q3 (see the text)
173
Comments on the Computed Yield Maps
Genera 1
In the following section the computed yield map will be discussed and compared to known conditions district by district. Figure 6.70 is a region map compiled from the district maps and diminished to present a convenient overall view of the region. In the last part of the section we provide a village list where the highest yielding block has been given within a circle of 3 km from each village center. "Number" in the map legend refers to number of lxl km blocks wi~hin each yield class; "upper/lower" limits g~ve the interval in m /s, corresponding to the marked values in m/h.
A. Igunga and Nzega Districts
The two districts being shown on the same map Fig. 6.71 will be commented together.
There is a striking resemblance.between the geology map and the yield map which of course would be expected with the methodology employed. To the north are the nyanzian formations which present in general mod~rate yields; the most common block to the northwest yields 3-4 m /h. Four boreholes carrying information on the yield are drilled in this part: 124/78 WMP 5-108, 125/78 WMP 5-109, 62/72, 23/60 and 111/70. The two first ones belong to the Nata representative area and are discussed in Chapter 2 2f this volume. 62/72 and 23/60 dischargi2g 2.7 (01) 4.0 (O?) m /h see Table 6.11 .and 3.2 (0,) 3.6 (02) m /h 3 respectively agree well with the computed yield§ of 4 and 3 m /h respe3tively. Borehole 111/70 discharged 6.2 m /h by airlift ~nd 5.0 m /h calculated from lithology; and computed map reads 3 m/h.
To the northeast are the vast areas of lacustrine deposits of large thickness. The chances for high deep ground water yields here are extremely small and drillings here is thus very haza rdous.
Leaving the nyanzian area and the lacustrine deposits and going towards the south the granite area is entered. The most striking features are the high yield blocks in compliance with the structures mostly running in southeast northwesterly direction. The most prominent one is the faultline associated with the Kagongo basin which runs from north to south in the middle of the map. A carefully sited borehole !n one of those structure blocks produces between 9 and 15 m/h.
-
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A few attempts have been made to drill on the structures: 10/79 WMP 5-118, 15/79 WMP 5-119, 42/79 WMP 5-121 and 1/79 WMP 5-117.
The drilling of 10/79 obvio~sly missed the structured as the yield remained at about 3 m /h only. The yield situation around that particular block where the borehole is situated looks as follows.
434 4 11 11 11 11 4
The yield of the borehole 10/79 agrees consequently better with that of the block to the north, see also the description of resistivity profile 6-116, Volume 7.
The boreholes 15/79 and 42/79 are both situated in the same block, see description of resisti~ity profile 6-116, Volume 7. The two holes produce~ 2 and 10 m /h respectively and the block "promised" 15 m /h. The drillings were carried out after fairly extensive geophysical investigations and a few attempts were made before a high yielding hole was obtained. The situation emphasizes the need of careful preinvestigations and perhaps a few attempts of drilling before obtaining a high yielding borehole in these types of formations.
Boreholes 1/79 WMP 5-117 managed to hit a structure by means of geophysical investigations; see description of Seismic profile 6-209 Volume 7. The c~mputed map promises 11 m /h; airlift t~st of 1/79 gave 13 m /h and well test a safe yield of 6.8 m /h (however, this latter result is a limit of the pump capacity rather than the aquifer). Apart from the structures the granitic areas of the middle and southern parts of3Nzega and Igunga districts produces yields ran~ing from 2 to 5 m/h. Borehole 148/78 discharged about 2 m /h with the following situation around it:
440 3 0 0 3 0 0
Borehole 267/76 was drilled in a 4 m3/h block but hit obviously a structure which is visible only at the adjacent bloc§s to the west and southwest. The borehole discharged about 14 m /h at the following situation.
3 3 0 11 4 4 11 3 4
('" ". :2 3 5 . 234 m '" '" "Hg '" !. 227
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Urambo District (Figure 6.72)
The major part of Urambo District carries granitic and gneissic bedrock which produces fairly moderate yields 3-4 m3/h. A few boreho1es produce yields of about the same magnitude as the computed:
BH No. Location Ql .Qz .9.4 computed
143/76 Igaga1a 6.8 6.5 4 130/75 Igaga1a 4.5 6.8 4 47/73 Urambo 5.7 7.6 4 Structure according
to BH record 3/69 Urambo Prison 4.7 4.5 3 3/67 Kal'iua 5.4 4 Well tested 2.3 m3/h
BH 64 U1yanku1u 6.5 6.8 4 BH 42 U1yanku1u 2.3 2.8 4 BH 40 U1yanku1u 1.2 2.8 3.8
To the west of the district when entering the vast alluvial plains the yields decrease considerably.
The most interesting formations from ground water pOint of view are undoubtedly as previously discussed, the structures. The district is intersected by several lineaments most of them running in southwest northeasterly direction and increasing the possible yields at least two times. Unfortunately none of the existing boreho1es have managed to hit any of'the structures.
BH 12/76 was drilled in a structure block promising 10 m3/h but obviously missed the lineament as the yield stayed at 4 m3/h. The situation around the boreho1e looks as follows:
10 4 3 4 10 4 4 10 10
The opposite situation can be studied at BH 32/66 which was drilled in a 3 m3/h block. However the borehole produced 10-13 m3/h. In this case there is a structure block in the northeast which obviously continues to the southwest but invisibly on the ground surface.
4410 333 3 4 4
• 178
The yield of BH 70/74 at Uyowa is an example of the presence of structures invisible on the ground surface and consequently not mapped. In this case there are no structure blocks at all in the vicinity of the actual block which promises 4 m3/h. The borehole 70/74 yielded about 12 m3/h. The situation shows that all structures are not necessarily visible on the ground surface and hence mapped in this investigation. It is possible to find additional waterbearing formations but one have in general to spend more efforts on preinvestigations to be able to carry out a successful drilling.
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The area of the Tabora district is so big that it has been divided into two maps Tabora district (north) and Tabora district (south). The northern part of the district shows great similarities with the southern parts of Nzega and Igunga districts.
The granitic and gneissic areas continues from the north yielding between 2 and 5 m3/h. A few boreholes indicate that the computed yields are in the right magnitude:
BH No.
66/78 1/77
119/72
Location
. Uramba Upuge Tumbi
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A few boreholesproduce less yield than the computed for that particular block. In these cases the block is surrounded by low yield blocks:
BH 106/78 WMP 5-106 Tumbi representative area see Chapter 2 of this volume:
Yield 1.1 m3/h 0 4 0 4 4 0 4 0 3
BH 68/78 WMP 5-104 Kapande yield 0.7 m3/h:
3 4 4 3 4 0 4 3 3
BH 60/75 Tumbi yield 1.1 m3/h:
4 4 4 0 4 4 0 0 3
BH 238/74 Tumbi yield 1.1 m3/h:
4 0 0 4 4 4 4 0 4
The yields of the three last boreholes are much lower than promised but the presence of low yield blocks around the actual one may serve as a warning for siting in the particular area unless careful preinvestigations are carried out.
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One special problematic area seems to be that peneplanized landscape west of Sikonge where the ground water situation seems not very promising. Deep ground water exploitation there takes a lot of preinvestigations.
The intrusive rocks of the district have been intersected by several dykes and disturbed by fau lts. There is no doubt that those features are the main sources for extraction of deep ground water. Presence of a lineament increases the yield about twice while a faultline makes it possible to obtain about three times the "norma 1" yi el d.
The most important structure is the continuation towards south of the faultline causing the Kagongo basin. There are also several tectonic movements associated with this fault causing lineaments and minor faults mainly to the east of the Kagongofault. Apart from this complex there are several lineaments and minor faults e.g. west of Sikonge, which might serve as targets for deep ground water drilling.
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184
Village List (Appendix 1)
In order to ease the interpretation of the yeild map an appendix has been prepared where all villages in Tabora region have been listed. The computer has been programmed to select the optimum yield block within a §ircle of 3 km from the village center. The yields are given in m/day (24 hours).
Values given e.g. 6.2998E-03 means 6.3xlO-3 m3/day and in practice no deep groundwater available.
The columns to the right give the UTM for the actual block.
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185
Geological and Hydrogeological Report on Shallow Dug Wells
This section reviews the geological and hydrogeological results of the shallow well investigations. In Volume 3 the survey results as to aquifer types, reli.ability, geology and land class were presented. To investigate in more detail the hydrogeology pump tests were carried out on thirty three wells. The results of this work are reported herein.
For shallow wells investigations the land classes used in the Water Master Plan have been combined into the following categories:
a. Filled valleys (Land class, alluvial deposits) b. Lateritic horizon (deep soils) c. Deep residual soil horizon (deep soils) d. Shallow residual soil horizon (shallow soils) e. Lacustrine deposits (lacustrine deposits) f. Weathered rocks (shallow soils)
The shallow aquifers with greatest potential in this region are situated in the filled valleys. These valleys are filled up with quaternary sediments consisting of silty clay to sand. They exhibit some geomorphological as well as certain other advantages over the other land classes, which are indicative of greater groundwater potential. These valleys occur at locallY the topographically lowest level and thereby possess the advantage of accumulating surface run-off for percolation into the aquifer. The top soil is usually silty loam to sand-loam which is more pervious for vertical percolation of surface run-off. The most promising shallow wells were encountered in this horizon at Usoke Railway.Station, Kaliua Railway Station, Sikonge (Tabora district) and Mwangoye and Igusule (Nzega District). Most of these are fitted with diesel pumps and serve as water sources for moderately large scale water supply scheme. This formation is most favorable for the development of large diameter shallow dug wells. These filled valleys are widely distributed all over the region. Of course their size and shape are not uniform everywhere. These filled valleys are indicated in the land class map and geological map within the alluvial deposits. Atypical cross-section of the aquifer is given in Figure 6.75.
Of the 162 shallow wells inventoried, twenty wells were located in alluvial depOSits (Filled Valley). Out of these twenty wells, fourteen were selected for repeat water level measurements. The result of which is given subsequently.
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186
h~!~ri!i£_~2ri~2~ (Figure 6.76)
This horizon is distributed in different parts of the region particularly Urambo district and south of Tabora district around Sikonge, Ipo1e and Chabutwa. A number of shallow wells were encountered in this horizon.
There are three types of 1aterite were encountered in region viz (a) hardcrust 1ateritic; (b) disintegrated (murrum type); and (c) 1ateritic clay. Hardcrust and disintegrated 1ateritic consists of sma:ll piso1itic modules of brown impure haematite and coarse quartz grains cemented together wi th 1 imoni te. Partially weathered pieces of the mother rock is often found associated with it. It is vesicular and water flows freely through it. In general disintegrated murrum 1aterite is more permeable than the hardcrust 1aterite. In some parts of the region, particularly around Iga1u1a (east of Tabora) a clayey 1ateritic horizon was encountered which is very sticky, plastic and permeability is very low. This clay horizon is not suitable for shallow well development.
In the Urambo district, in and around Itundu, Urambo, Kaliua, Igaga1a, Kazaroho, Igwisi, Kalemela and Urambo town the overburden generally consists of wide thickness succeeded by a fairly porous weathered bedrock. This formation is also encountered in and around Izimbili, Tumbi, Sikonge, Ipole, Chabutwa, Igalula and Upuge (Tabora district) and in and around Zogoro, Nata, Mywangowe, Bukene etc. (Nzega district). The water table in these areas generally follows the surface topography. In some parts of this region effluent seepages from the upland slopes form good ground water aquifers. These seepages percolate through laterite and along the weathered profile resulting in considerable discharge during the wet months.
Of the shallow wells inventoried, forty six wells were located in this horizon. Out of these twenty one were selected for repeat water level measurements.
The deep residual soil horizon consists mainly of sands, variable in composition, color and size. These sands are not generally well graded. Judged by the case of vertical infiltration this horizon is very promising. This class is distributed in different parts of this region as marked on the geological map.
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187
TYPE I: TYPICAL CROSS-SECTION OF SHALLOW WELL IN THE FILLED VALLEYS -ALLUVIAL DEPOSITS
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TYPE IV: TYPICAL CROSS-SECTION OF SHALLOW WELL IN THE RESIDUAL SOILS (DEEP)
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189
Fifty three shallow wells were located in this horizon and nineteen wells were selected for repeat water level measurements.
Four wells were selected for pumping test. The average optimum yield is 0.024 m3/min (standard deviation 0.028 m3/min).
d. ~b~llQ~_B~~ig~~I_~Qil_~Q~i~QQ (Figure 6.78)
This horizon also consists of sands, variable in composition, color and size like the deep residual soil horizon. Only here the depth to bedrock is less than 5 m. In this horizon some of the wells are reported by the villagers to go dry during the dry months, (September to December). But during the course of present survey (April 1978 to April 1979) very few dry wells are found even during the driest months. This is probably due to high rainfalls during the years 1977-78, compared to previous years. Shallow residual soil horizon followed by uniformly weathered profile is more promising for ground water. This horizon has been demarked and shown in the land class map.
Forty two shallow wells were located in this horizon and twenty nine were selected for repeat water level measurements.
Northeastern part of this region (Igunga District) the areas in and around Igunga. Igurubi, Mbutu, Sakamaliwa, ~1vJamashinga, Itunduru are covered with lacustrine deposits. The whole surface is to a great extent covered with black cotton soil usually up to a depth of 1 m, followed by calcareous deposits such as highly fractured soils. Few shallow wells are found in this formation. There are five shallow wells around Sakamaliwa (Igunga District) - one is lined and the others are unlined. The depth of these shallow wells vary from 10 to 12 m below ground level and water table varies from 7 to 9 m below ground level. The main aquifer is impure limestone to calcrete which is highly jointed and fractured. Near Igurubi, there are about 100 water holes (shallow unlined wells) scattered over 1 Sq.k.l. area. The internal diameter varies from 0.5 to 1.0 m and the depth varies from 5 to 7 m below ground level. The aquifer is mainly calcareous sandy silty clay. Little seepage of water generally occur at the bottom of the well. People used to fetch 3 to 4 buckets (approximately 0.0035 to 0.004 m3) at a time and wait for one hour for recovery. The wells are some places located even 1 m apart. These series of wells are situated within the lacustrine deposits. These are the only two localities within the lacustrine deposits where we have encountered dug shallow wells, remaining parts of lacustrine deposits are completely devoid of any shallow well.
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All the rock types have been subjected to strains due to tectonic causes and fissures have resulted. In the granite these fissures are in the nature of joints, generally at right angles to each other, trending NE-SW and NW-SE. Some places it is better developed than the other places. This jOinting in the granite store up under ground a considerable amount of water in its joint planes, but from the field evidence it has been observed that in many places, these joints have been sealed up with clay and secondary minerals due to weathering so as to become ineffective as underground water reservoirs. Generally, there are three sets of joints in the area under investigations: (i) vertical joints or tension joints; (ii) angular or longitudinal joints or sheer joints; and (iii) horizontal or secondary joints. Generally, vertical and angular jOints which yield water. Horizontal joints are generally filled up with secondary minerals. But interconnected jOints are more promising and potential for ground water. Wide and deep joints are quite favorable as a good conduit for ground water movement and storage. These joints and fissures may hold considerable amount of water. But many areas in this region these joints and fissures have extended below the economic limit which is not favorable for shallow dug well sinking. In this region there are very few shallow wells in this horizon. Most of the cases this horizon is lying under the residual soil horizon or laterite regolith.
191
3.5 Pumping Test Methodology, Shallow Wells
There is practically no standard formula to determine the aquifer potential of shallow dug wells. All the standard procedures have some deficiencies to determine the optimum yield of large dug diameter shallow wells.
The practical problems to determine the aquifer potential of shallow dug wells are as follows:
a. No proper pump is available to control the yield as low capacity as per as 0.008 m3/min. Honda pump's capacity is 0.25 m3 to 0.4 m3/minute. So within a few minutes the pump empties the well.
b. Most of the unlined shallow wells are not of regular shape down to the bottom. Due to this irregularity, water stored in the well cannot be easily calculated.
It is not always practical to pump the well for few minutes at high capacity and wait till the water level to recover the original level. To overcome this practical problem it is necessary to determine the optimum yield of the shallow well.
Dr. Jasminko Karanjac*has established one method to calculate the optimum yield of the dug shallow wells, considering all the factors mentioned above 33 dug shallow wells were tested with a Honda pump (capacity 0.25 m3/min to 0.40 m3/min) in Tabora region. The pumped wells were chosen with respect to different land classes.
The Methodology is as follows:
The well is pumped at the available pump capacity. The pump discharge is measured and the pumping time noted in which a substantial drawdown is created in the well (or well emptied). The pump is then stopped the time needed for recharge to fi n up the well up to the original static water level is recorded (pre-pumping water level).
* Dr. Jasminko Karanjac, Energo Project Co. Leleni Venac 18 11000 Beogard, Yugoslavia IT, Jrl. of Ground water, NWWA -July - August 1975, Vol. 13. No. 4
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192
The volume of water that refills the well after the pump is stopped, Vrec, will be defined by the following equation:
Vrec = /R Qrec (t) dt " QR tR ............... (1) o
where:
Qrec (t)
tR
QR
is variable inflow into the well
is the recovery time
is an equivalent average inflow rate from the aquifer during the time of well recovery. This quantity is an empirical expression of what might termed "optimum yield of the well"
The total volume of water discharged from the well during the time of pumping tp can be separated into two parts (1) volume of water stored in the well between free and pos t pumpi ng level and (2) volume of water that aquifer yield to the well during tp.
Mathematically this can be expressed as:
tp tR tp J Qp dt = f Q rec (t) dt + J Qaq.(t) dt .... (2)
o o o
Proper mathematical expression of the balance of mass in the case of fully penetrating well with uniform well geometry is the following equation:
2 rrrw T Jtp ds(rwt) dt - rrr2w dr o
where:
is the transmissivity of the aquifer is the effective radius of the well is the drawdown in the aquifer
tp J Qp dt ... (3)
o
T rw s sw is the drawdown in the well at time t.
Equation (3) express the fact that the total discharge of the well during the pumping time tp is equal to the sum of the volume of water that aquifer yield to the well and the volume of water stored within the well.
193
Equation (3) is but one boundary condition of a boundary value problem. Instead, an approximation of the following type has advocated by Dr. Karanjac.
The integral on the left hand reduces to Qp tp, where Qp is QR tR and QR tp respectively. semi-empirical expression for
side of Equation (2) radially the steady pumping discharge, With this approximation a
the
QR =
i . e.
Qp tp tp+tR
QR results.
is the optimum yield of the well is the pumpi ng rate is the pumping time
(4 )
QR Op tp tR is the recovery time to original static water level.
This method has been applied and the results are given in the list of shallow wells given at the end of this chapter.
Shallow Well - Control of Ground Water Levels
The control of the ground water levels in the selected shallow wells started in April-May 1978 and continued up to April 1979 thus comprising a full year cycle. The result of the control program shows that the main categories of aquifers supplying shallow wells in the region are:
1. Alluvial soils (filled valleys - river courses) 2. Lateritic soils 3. Residual soils deep 4. Residual soils shallow 5. Lacustrine deposits
Unfortunately the control program of the shallow wells dug in lacustrine deposits could not be fulfilled due to transport problems particularly during the rainy season when the area is inaccessible for vehicles.
The results have been compiled and are shown in Figure 6.82. To the left are the annual fluctuations - the differences between the highest measured ground water level and the lowest. Those values have been shown for each category of geological environments.
Regarding the alluvium category one may note the comparatively small fluctuations averaging .8 m which means that wells dug in this aquifer need not be dug more than some 1.5 m below the highest SWL to keep it from going dry.
I':
"
,. ,.(
-
1 '.
194
The laterite category shows a greater spread of values. Looking at the regional distribution of those wells the values to the left are collected from the peneplanized area around Sikonge where the wells dug in the lateri te "blankets" obvi ous ly vary less than laterite wells from the other parts of the region. On average in the region a well dug in laterite should be some 3 meters below "normal" SWL.
Deep residual soil shows an average drop of water level of 1.5 m which means the well needs be dug about 2 m below normal SWL. Wells dug in shallow residual soils show a slightly higher average drop 1.8 m so the annual fluctuations imply a well should be dug about 2.5 m below high SWL to prevent it from going dry.
To the right in Figure 6.79 collected in the histogram to illustrate the changes in SWL
These shallow wells are:
one typi ca 1 well the left has been during the record
Alluvium Lateri te
out of those chosen to peri od.
4:2078 4: 2072 4:2050 4:2089
Chekeleni Kaliua Bukene Kipalapala
Residual soil, deep Residual soil, shallow
The detailed description of these wells is found in Volume 3S.
The results of the water level measurements have been plotted on diagrams, see figure 6.79.
The following comments can be made on the results.
The well 4:2078 is situated in a wide valley and the aquifer seems to offer a sufficient water supply for the well during the year. The well is very shallow, the bottom only 1.25 m below the ground level but the water inflow seems to be enough also during SeptembGr - October when the effect of the dry period influences the water level in the well considerably. The water level sinks from 0.6 m in May-June to 0.7 m in August and then finally to 1.2 m in October. The effect of the beginning of the rains is reflected clearly as the level is rising from October to December to 0.35 m below ground level. It is characteristic for a good aquifer that the variation during the year is comparatively small, here about 1 m only.
The well 4:2072 Kaliua shows the same rhythm as the Chekeleni well during the year but the variation is larger. The level is sinking from April-May 2.7 m to 4.4 m in October and then is recuperating again during December-January to 3 m and 2.5 m. This variation
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7 HALLOW RESIDUAL SOIL
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3 4 5 mbg l A M J J A SON D J F
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1,0
1,5
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KIPALAPALA 4,2089
... 3,5 i==~====~~=~=="1
3.6
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-196
of the level is reflected in the depth of the well the bottom being at 5.0 m below the ground level. The behavior of the ground water shows that the movements in the lateritic aquifer are comparatively slow compared with the alluvium.
The results of the investigation of the aquifer "deep residual soil" 4:2050 Bukene, again indicate a slow reaction on the precipitation cycle. The lowest water level, 1.8 m is recorded in November and then stepwise is moving upwards again to 0.7 m. The comparatively small span indicates here as well as in the alluvium a comparatively good aquifer with rather fast water movements in the aqui fer. The moderate depth of the well, 2.5 m is also significant for a good water supply of this type aquifer throughout the year. The well is located on the slope of a comparatively wide valley which is aprt of the criteria for a good well.
The well 4:2089 Kipalapala which is located in shallow re~idual soil on a hilly area reflects the precipitation conditions faster. The water level is sinking to its lowest pOint, 2.5 m, in August-September and is then rather constant through OctoberNovember. During December it is going upwards again and reaches 0.9 m in April. The depth of the well is 3.6 m which indicates that the capacity of the aquifer sometimes is decreasing which forces a deepening of the well.
Shallow Ground Water Potential Estimates
The basic information for the estimations of the shallow ground water potential is collected from well-tests performed in existing shallow wells in the region and regional geological data supported by data as soil analysis.
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One of the basic ideas behind the following calculations is that the annual drop of the shallow ground water level during the dry season does not affect the yield of the shallow well. The range of those fluctuations has been related to the geology class and are described in the previous section. In the following it is consequently assumed that the drawdown caused by the yield follows the annua 1 drop of the water 1 eve 1. The well mus t then be so deep that the drawdown does not drop below the bottom of the well at the particular part of the year when the unaffected ground water level reaches its lowest position. The deeper the shallow well the more expensive; we concentrate in what follows on the mi nimum depth of a we 11 to estab 1 ish a reasonable re 1 i abil i ty.
197
A shallow well might be considered as a partly penetrating well of the main aquifer out of which the deep ground water well yields its water. The length of water entry is less than the total depth of the aquifer. We assume an unconfined isotropic aquifer and steady state conditions.
The following equation will be valid:
where:
Q K H hw
hs
H - hw = l 4nK
lnn.hs 2rw
is is is is
is
the extraction rate the permeability the total thickness of the aquifer; undisturbed conditions the distance between ground water level in the well and the bottom of the aquifer.
the distance between the original undisturbed ground water level and the bottom of the shallow well.
See Figure 6.80.
For each of the eight geology classes we know the depth to bedrock 0, the static water level O-H and the permeability K. The values are collected from the shallow well inventory and pump-tests carried out at the Wt~P (see below).
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198
• rw ,-
~ F' a/{~I(_I/&rt: N& //~ rr·-I/crtF I.S!"II~"'-::'I: p ',.-=-1', ~/(.s=' //~r/#I', :::://'#"~r~u-""" '/;:/1.-
SWL -- - - - - -- - --
~ hs \
r
et hw
FIGURE 6.80 Steady flow to a well partly penetrating an unconfined aquifer.
H
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2)
3)
4)
5)
6)
7-8)
199
~~!i~~!i~9_!b~_E~r~~~!~r~_fQr_~~1~~1~!iQ~_Qf_~b~11Q~_~~ll Ground VJater Potential ----------------------The results from the shallow well inventory have been compiled with respect to each geology class and listed below:
TABLE 6.12
PARAMETERS DERIVED FROM THE SHALLOW WELL INVENTORY IN TABORA REG.
Geology Class Static Water Depth of Thickness of Permeabi 1 i ty* Level m.b.g.l. Well (m) Aguifer (nl) m/s
Alluvium 1.5 2.9 22 5 x 10-5
Lacustrine Dep. 8 10 40 1 x 10-7
Deep Soil Lat. 3.8 5.4 18 2 x 10-6
Bukoban Form. 2.8 4.0 18 3 x 10-5
Ubendian Form. 3.0 4.2 18 5 x 10-6
Nyanzian Form. 3.8 5.4 45 1 x 10-6
Sha 11 ow Resi-dual Soil over Granite and Gneiss 3.1 4.3 5 1 x 10-6
The permeabilities are calculated from lithology.
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In the table below depths of the wells with respect to different extraction rates has been calculated for each geology class. As 0.3 m ha o to be allowed for the inlet of pump the expression on the left .and side of the equation on page will be hs - 0.3 instead of H - hw·
Using the parameters from Table 6.12 solve the equation for Q = 2 m3/h Q = The results are given in Table 6.13.
in the previous section we 3 m3/h and Q = 5 m3/h.
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200
TABLE 6 .. 13 - RESULTS OF DEPTH CALCULATIONS; SHALLOW WELLS
1.
2.
3.
Alluvium
Q = 2,0 m3/day Q = 3,0 " Q = 5,0 "
Lacustrine Deposites
Q = 2,0 m3/day Q = 3,0 " Q=5,0"
Deep soi 1
Q = 2,0 m3/day Q=3,0" Q = 5,0 "
4. Bukoban Form
Q = 2,0 m3/day Q = 3,0 " Q = 5,0 "
5. Ubendi an Form
Q = 2,0 m3/day Q = 3,0 " Q = 5,0 "
6. Nyanzian Form
Q = 2,0 m3/day Q = 3,0 " Q = 5,0 "
H = 22 m H = 22 " H = 22 "
H = 40 m H = 40 " H = 40 "
H = 18 m H = 18 " H = 18 "
H = 18 m H = 18 " H = 18 "
H = 18 m H = 18 " H = 18 "
H = 45 m H = 45 " H = 45 "
7-8. Soil over Granite/Gneiss
Q = 2,0 m3/day Q = 3,0 " Q = 5,0 "
H = 5 m H = 5 " H = 5 "
K = 5x1(~ K = 5x10_5 K = 5x10
K = 1Xl0=~ K = 1x10_7 K = 1x10
K = 2X1(~ K = 2xl0_6 K = 2x10
K = 3x1(~ K = 3xl0_5 K = 3xl0
K = 5Xl(~ K = 5xl0_6 K = 5x10
K = 1Xl0=~ K = 1x10_6 K = 1xl0
K = lXl(~ K = lxl0_6 K = lx10
H-hw = 0,26 m H-hw = 0,31 " H-hw = 0,36 "
H-hw = 0,35 m H-hw = 0,35 " h-hw = 0,35 "
H-hw = 1,94 m H-hw = 2,49 " H-hw = 3,41 "
H-hw = 0,36 m H-hw = 0,36 " H-hw = 0,40 "
H-hw = 1,07 m H-hw = 1,40 " H-hw = 1,94 "
H-hw = 2,96 m H-hw = 3,79 " H-hw = 5,14 "
H-hw = 3,01 m H-hw = 3,85 " H-hw = 5,24 "
Reg'd Depth
3,2 m
10,4 m
7,9 m
4,4 m
5,6 m
9,2 m
8,2 m
Well No.
4:2029
4:2040 4:2044 4:2055 4:2037 4:2039
4:2036 4:2056
4:2017 4:2021 4:2013
4:2006 4:2009 4:2001 4: 2011
201
The depth of the well must be the lowest static water level plus the drawdown of the well as given from the above equation.
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In order to check that appropriate values for the permeability have been used a number of tested wellshave been used applying the above formula for partly penetrating wells. At this calculation the optimum yield and the actual Hs Rw and H - hw have been taken from the well test data in the appendix. In some cases H have been known from additional investigations and consequently used in the calculation. Otherwise the estimated H for the actual geology class of each well have been used.
The results of the calculation have been listed by district in compliance with the well test data.
Diagrams 6.81 - 83 are compilation of permeability data from each of the three geology classes represented 1, 3 and 7-8 where the permeability calculated as above is compared to the value calculated from the lithology.
TABLE 6.14. CONTROL OF PERMEABILITY ESTIMATIONS.
District: Nzega
Q
1.3'10-4
2.0'10-4
1.3'10-4
1.6.10-4
1.8.10-4
Hs Rw H Hw K
7.87.16-6
1.89'10-5
1.34'10-5
2.50.10- 5
3.63'10- 5
6.78'10- 5
2.07.10-5
1. 55 '10-5
K 1 ith. Geology Class
2.16.10-4
6.6'10- 5
9.5'10-5
2.95 1.8 7.20 1.30 1. 76 1.80
1.80 2.89
District: Igunga 1 . 1 . 10-4 1 .94 1.3'10-4 6.45
2.5'10-4 2.27 4.16'10-4 1.03 3. 8 . 10-4 0 . 88
2.8'10-4 1.25
2.66'10-4 2.57
0.5 0.5 0.74 0.60
0.52 0.50 0.50
1. 25
16.15 14.60 11.2
11.9 3.96 4.20 4.15
21.09
0.50 3.64
0.45 6.45 0.50 3.64 0.50 3.57
0.57 17.68 0.50 20.72 0.71 19.7
H = depth of well
14.15 12.97 10.6 10.93 3.19
3.70 3.65
20.65
2.74 4.86
3.34 2.97
17.10 19.72
19.26
1.87.10-5
6.48'10-6
1 .18 '10-4
1. 29 '10- 4
1.06.10-4
4.90'10-5
6.56.10-5
3.5.10-5
10-6
10-6
10-6
4.8'10- 5
10-6
10-6
3.9.10- 5
4.9'10-5
4.0.10- 5
10-6
5.8'10-5
5.9.10- 5
6.6'10-5
3.9'10-5
3
3
3
3
7-8 7-8 7-8 1
7-8
7-8 * 7-8 7-8
202
District: Tabora
Well No. il Hs Rw H Hw
4:2086 4.2.10- 4 1.48 0.58 19.93 18.7
4:2102 1.1.10-3 3.63 2.15 17.07 16.6
4:2093 1.8.10-4 2.78 0.50 20.78 18.15
4:2089 4.0.10-4 1.28 1.0 2.28 1.14
4: 2112 1. 8.10-4 2.12 0.50 13.92 12.00
4:2109 1.6.10-4 0.90 0.60 14.25 13.52
4:2094 2.16.W4 0.92 1.30 1. 92 1.32
4:419 4.5.10 -4 0.95 1.0 2.15 1. 70
Distri et: Urambo
4:2082 1.2.10-3 3.31 2.0 6.30 5.54
4: 2072 1.6.10-4 1. 28 0.50 14.0 12.95
4:2071 2.6.10- 4 2.83 0.50 14.58 11.85
4:413 1.5.10-4 0.92 0.75 12.08 11.17
4:415 2.3.10- 4 4.70 0.70 12.98 11. 14
4:414 1.5.10-4 0.52 0.60 12.07 11.60
4:2073 3.3.10-4 2.40 0.62 13.5 11.60
4:416 3.3.10-4 1. 18 0.60 14.68 13.56
4:2078 3.16.10-4 1.04 0.50 26.68 25.82
See Volume 7, Section 3.6.2
K K Lith
5.13.10-5 5.2.10-5
4.37.10- 5 4.6.10-5
9.86.10-6 3.19.10-7
3.29.10-5 6.3.10 -5
1.35.10-5 10-6
3.35.10-5 10-6
9.58.10-6 10-6
7.45.10-5 10-6
7.65.10-5 3.74·10-5
2.65.10-5 10-6
1.18.10 -5 10-6
1.69.10 -5 10-6
1.01.10-5 10-6
3.06.10- 5 10-6
2.10.10-5 10-6
4.51.10-5 10-6
6.7·10-5 3.16.10-5
Geology Class
1
3
1
7-8
3
3
7-8
7-8
1 ;It
3
3
3
3
3
3
3 1 ;It
I
:1
I il ,
, ,
li j
+' Vl -, ,
203
M/~~c 10 _______________ +-_______ -t-______ _._-.,;t:
-5 10 _____ -+ __ _
-5 Chosen value 5 x 10 M/Sec
G> 0·
10-6+--__ --1 _________ ~~----------+--- -------f
10- 7 +-_~jL_- ----------+----------f---------
10- 7
I'l : Tabora )( : Nzega 0 Urambo • Igunga
FIGURE 6.81
10-6 10-5
Relationship between K (lithology) and K (welltest) Geology class 1.
10-4
M/sec K(lith)
~ ....,
: ~1 ~ ~
<lJ
12:'f ~
2.04
M/se 10-4+-__ -+ _________________ 4-______________ ~~--------------+
x
10-6 10-5 10-4 M/sec K (lith)
(i] Tabora
k Nzega
<i> Urambo
• Igunga
FIGURE 6.82 Relationship between K (lithology) and K (welltest) Geology class 3.
205
____ ~----------------+----------------T--------------
10-6
El • Tabora
" Nzega
~ Urambo
• Igunga
-6 Chosen value 2 x 10 M/sec
------- ----+--
10-5 I 10-4 M/sec
FIGURE 6.83 Relationship between K (lithology) and K (welltest) Geology class 7-8.
K(lith)
1.
2.
206
Geology Class 1: Alluvium (Fig.6.81)
The compari son di agram fi g. 6.81 shows good agreement between the calculated K-va1ues and tne one 5xlO-5 chosen to be representative for the geology class.
Geology Class 3: Deep Soil (Fig.6.82)
The K-value derived from well tests are mostly between lxlO-5 and 5xlO- 5. Still the difference between the chosen permeability lxlO- 5 and those ten times higher is fairly small and not of great importance within such a low range of permeability values.
3. Geology Class 7-S Shallow Soil over Granite and Gneiss (Fig.6.S3)
The values in this class are very spread out and the permeability of 2 x 10-6 chosen to be appropriate is on the safe side.
I 207
CHAPTER 4 HYDROGEOLOGICAL INVESTIGATIONS
This chapter presents some practical comments on hydrogeological field investigations. This is not meant to be a comprehensive listing but only points of interest reflecting the Consultant's experience particularly during the Tabora Water Master Plan field investigations.
4.1 Organization and Conduct of Resistivity and ~1agnetic Surveys
B§~iHi~HY
Proper planning and choice of configuration, maximum electrode spacing, probe spacing, and profile siting are essential. The following observations are made:
Planning
Configuration
Decisions on geo-electrical survey method should be taken with respect to factors as geology and topography and additional data e.g. old drillings. In the Tabora Region W~lP the Schlumbergerconfiguration was chosen being the most efficient for the purposes of the WMP. This also depended on the fact that master curves for field interpretation were available. The measuring program comprises double segments of the field curves (see 7.1.3). Hence the field work becomes more extensive but the comparatively little loss in time corresponds well, in our opinion, to the raise in reliability of each sounding. Hence, not one single sounding carried out at the WMP had to be excluded because of irregularities in the measured values.
Electrode Spacing
An important matter is the decision on the maximum electrode spacing which should be chosen with respect to the desired depth of the investigation. In the survey carried out for the WMP, determination of depth to fresh bedrock has been the most important target as this depth is an important factor in determining the hydro-geological potential. This meant that the maximum electrode-spacing was chosen to be 2-3 times the expected thickness of the overburden, which means AB/2 ~ 300-400 m. To be sure of the fact that fresh bedrock was always reached this electrode-spacing was used routinely.
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208
Probe Spacing
The probe-spacing should be determined with respect to the desired accuracy at every profile-site and was, during the investigations of the WMP, adjusted between 50 and 100 m. The distance 100 m appeared to be sufficient in most cases, so was used routinely in the short profile program. The direction of the array was carried out perpendicular to the profile unless features as outcrops, brooks, etc. made this impossible. Levelling of the profiles should take place at the same time as the resistivity mea"surements.
In the long profile program, the probes were carried out two by two some 200-400 m apart in each valley track. One was taken perpendicular, the other parallel to the road.
The distance between the valley-tracks decides of course the distance between each couple of probes, but 3 km was common.
Siti ng
The siting of resistivity profiles should be carried out by geologist/geophysicist with respect to geology, topography, air photos, airborne geophysics (if available) etc. Presence of bushy terra i n wi 11 de 1 ay the measurements and shoul d be avoi ded. As the resistivity technique presumes plane-parallel layers, this fact should be kept in mind at the siting and the profiles should, if possible, be sited on flat land.
Resistivity Team Composition
"A team operating one set of resistivity equipment should be composed as follows:
Team Crew
Operator (water technician)
Responsibi 1 ities
Supervise team, take readings and calculate and plot curves.
2) Driver
3-6) Labors (1-2 might be local) Measure and move electrodes.
For transport of one team, one landrover is sufficient. If many teams work together a truck is recommended for the heavy and space-consuming part of the equipment as e.g. tents.
1 )
2)
209
Magnetic Investigations
Magnetic survey along the resistivity profiles has showed to be of great value especially when irregularities of the bedrock are struck. The magnetic profile was often extended in one or both directions especially when an anomaly was obtained and the shape of it was wished to be achieved properly.
The distance between the reading was normally 20 m but when anomaly values were struck it was decreased to 10-5 m.
Survey Crew
The resistivity/magnetic survey crew of the Tabora WMP consisted of two resistivity teams, composition as above and one magnetic survey and .levelling team. The latter which works in intimate coopera ti on with the two former cons is ted of two members.
Team Crew
Field surveyor
Field assistant
Responsibilities
Carry out the levelling and operate the magnetometer. Take the readings and plot the profiles.
Support the levelling and the magnetic profiling.
As this activity is finished quite soon at an investigation site the two team-members support one resistivity team each.
Equipment
Field equipment for the complete survey crew should be composed of following items:
2 Land Rovers
2 ABEM terrameters including V-box, G-box, batteries and connecting cable.
8 Cable-reels 8 Connecting cable 1 m with clams and plugs 8 Connecti ng cabl elm with plugs 8 Iron electrodes 8 Hammers 4 Measuring tapes, cloth or plastic 100 m 40 Harking sticks, wooden, small 1 Leve 11 i ng ins trument 1 Levelling stick 5 ~arking sticks, steel, 1.5 m 2 Umbrellas, for sun protection 2 Pads of VES forms 3 Electronic calculators 1 Camping equipment including 3 sets of tables and chairs
~",
210
Analysis and Interpretation
A well-trained team carries out 3-4 probes per day. The time for analyzing and interpretation of the field work depends on the length of the profiles, numbers of probes, the shape of the field-curves (= the number of the resistivity-layers) and availability of additional data. In "normal" cases with a profile length of 1 km, interpretation and analysis takes 2-3
'days. Many resistivity and magnetic profiles within the same area will increase the reliability of the interpreted results if the geology is not changing too much.
The interpretation should be carried out by an experienced geophysicist. In order to check and on some occasions interpret complicated resistivity field curves, a computer is needed. Several programs for making master curves as well as for semi automatic and automatic interpreting are available today. Magnetic anomalies were interpreted only qualitatively as a quantitative interpretation needs a considerable volume of additional data which was not available.
FIGURE 6.84. RESISTIVITY TEAM TAKING A READING ON THE ABEt1 TERRAMETER
~~. j.~:.}. )l"t
211
4.2 Operation of a Seismic Team
Based on the experience of the Tabora Water Master Plan a brief outline of the procedures for a seismic team is provided in the fo 11 owi ng:
The team should consist of the following staff:
l. 2. 3. 4. 5. 6. 7.
Seismic Engineer (team leader) Seismic Operator Shot master Driver Field Workers Cook Watchman (local)
1 1 1 1
3-4 1 1
The seismic engineer handles the interpretation of the seismic curves and profiles and writes the reports. The interpretation takes about twice as much time as the field work, thus the best solution is that an engineering geologist with long experience of the seismics performs the interpretation in coordination with other geophysical and geological working groups. In that way the operator can entirely deal with the field work and thus obtain rapid, accurate results.
Operator - Directs the field work, surveys and levels the profiles; responsible for the seismic equipment, the explosives and the crew.
Shot master - Responsible for the dynamite and the detonators, Handles the shot cable and charges the shot points.
Drivers - Responsible for the car and the transport; should be able to help the field workers.
Workers - Clear the area for the profile, measure the intervals between the shot points, prepare the shot points, move the geophone cables and place the geophones in the ground.
Cook - Responsible for food, water supply and storage, preparing food, keeping tents and the camp clean, guarding the camp during day time.
Watchman - Guarding the camp during the night.
Comments on Operation of the field team
It is important that everybody in the team knows his tasks and performs such efficiently. Taking into account all the difficulties
:::~:"'. ~r
r
212
that can occur during the field work such a breakdown of vehicles, illness, heavy rains, time consuming food and water supply, the effective working time during a week usually comprises four days. The daily working time usually is extended to 10 hours.
The length of profile that can be measured during one day depends upon the chosen interval between the geophones, 2 m, 5 m or 10 m. With 10 m interval a profile lengths of about 800 m can be completed in one day, with 5 m interval - 500 m and with 2 m interval - 400 m. These figures refer to results w.hen using the 12 channel ABEM seismic equipment. The 24 channel equipment increases the working capacity about 50%.
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Seismic unit and spares. Equipment recommended is AB EM TRIO 12 or 24 channel recorder-amplifier seismic refraction unit with fittings for charging the instrument. Shot box with one or seven channel - cable of the length of 25 m. 210-250 m single cables for 12 or 24 channel geophone cable. The interval between the geophone connectors is 10 m.
If the interval between the geophones is 2 or 5 m a 10 m geophone cable with 5 m interval between the connectors should be easier to handle. It is advisable to keep 4-6 geophones as a reserve. The consumption of the dynamite and the detonators is difficult to estimate.
~~~Ei~9_Sg~iE~~~!
If working in tropical conditions: Light tents (2 persons), beds, mattresses, sheets, mosquito net, shower tent, tables and chairs for every man in the team, several water cans, kitchen utensils, crockery and a gas-driven refrigerator.
Y§!bi~l§!
The team is living and working in the field usually for long periods and therefore the driver must keep the car in good order and should be able to carry out minor repairs.
4.3 Recommendations for Drilling Operations
The strategy of a dri 11 ing program for a water master plan project can be looked upon in two ways ei ther as' a pure research i nvestigation or as a combined investigation and production hole program, the latter phase of course being the secondary purpose or extra benefit of the results of the drilling.
213
Type of Drilling Unit and Organization
The choice of drilling unit is depending upon the targets in each particular project and also naturally the area to be investigated the topography, geology etc. and last but not least the accessibility of the drilling sites.
If the project is looked upon as research, light rotary drilling units can be used which is a great advantage for the movability and the flexibility of the field work. Usually the light rigs and drilling holes of small dimensions with continuous or interval sampling. Depending upon the type of method the samples are disturbed such as blown or augered soil samples and chips of bedrock. Undisturbed samples are collected with core drilling which is comparatively slower method but gives more accurate informations about the lithology. The rigs are able to drill with bigger dimensions for instance up to 20 or 25 cm through the overburden but in the bedrock usually not more than 10 cm and if core drilling 32-74 mm holes are the common dimension.
There is, however, a possibility to carry out core-drilling using 101 and 146 mm drilling bits which in that case allow bigger pumps with correspondingly larger capacities to be used.
So for a complete test program, holes with bigger dimension are a must which determines the size of drilling machine. This type of machine can drill bedrock holes of bigger dimension 16-25 cm and thus submersible pumps can be used for the well test with a diameter of 10 to 13 cm with maximum capacity varying from about 5 m3/hr to 40 m3/hr. The figures given are based upon the curves showing the capacity of the pump on different depths in the holes.
The operation of the big drilling units needs careful planning and for the field work a well organized transport team has to be created to avoid unnecessary delays of the drilling time which will jeopardize the outcome of the project. Particularly the fuel and the sparepart denvery has always been a bottleneck for the rig operations. If u rig has no movable workshop operating in the field a local workshop must be established, for instance, at the ~1AJI yard.
The following arrangement can be looked upon as examples how to organize a drilling unit.
1 )
1 )
4)
1 )
Staff --
Foreman
Dep. foreman
Workers (suggesting 2 2 workers per shift.)
Mechanic
214
shifts -
Eguipment
1 drill rig Schramm or similar
1 land rover with radio
1 truck with long flat, crane and hitch
1 fuel bowser, 3000 It. 1 water bowser, 2000 It.
If the unit is provided with a movable workshop it will be one driver for the workshop if the mechanic is not able to drive it.
Extra personnel such as watchmen should be employed locally.
If the work is carried out far from a depot one extra truck should be allocated to the unit for transport of fuel and spares.
~2Q!rQl_Qf_QrilliD9~_~Qr@nQl@_~Qg~_@!£·
One hydrogeologist should be in contact with the rig continuously and at times stay with the rig particularly when it is drilling for control of the collection of samples.
During the drilling the penetration rate should be measured very carefully, the timetaking, changes of bits, compressor etc. must be recorded properly.
During the drilling, analyses of the samples should be performed. If possible a well log unit should be able to control the hole and the unit must work together with, or be the responsibility of the hydrogeologist.
215
FIGURE 6.85 CHECKING THE SAMPLES. RIG 48 DRILLING AT NYANDEKWA
The possibi: ity to carry out well tests during the drill ing where waterbearing zones are struck is usually difficult but would be a great advantage. However the drilling team is often forced to pull out and finish a drilling as fast as possible due to fast climate changes which during the rainy season can lead to that the rig can be bogged down at a drilling site. Likewise the problem with transport and spares can delay the drilling seriously vlhich in tum vii 11 force the foreman to finish the hole when it is possible without delay i.e. he is drilling for water and when a satisfactory amount is I'eached, no matter if 2 or 3 waterbearing zones have been crossed, then the hole is completed. Itence immediately after completion the well test can be carried out.
216
FIGURE 6. 86 WELL TESTING OF'BH 106/78 TUMBI REPRESENTATIVE AREA
If the rig has been able to drill an observation hole the well test should begin with an aquifer test followed by a step drawdown test. Otherwise only the drawdown test can be carried out.
Water samples should be taken preferably during the drilling when water zones are struck if it is possible to clean the hole before sampling. Otherwise the sampling should be done after the completion and then during the well test two or three times to control if any changes of the water quality after continuous pumping.
21 7
FIGURE 6.87
CHECKING THE DRAWDDWN. AQUIFER TEST OF BH 106/78 TUMBI REPRESENTATIVE AREA
APPENDIX 6.1
VILLAGE LIST
COMPUTED YIELDS (MAXIMUM) WITHIN
A 3 KM CIRCLE ABOUT THE VILLAGE CENTER
~
t. .. A6.1-1
DEEP BOREHOLE PO TEN TI A L
t. NAME VIL NR YIELD UTM-X UTI'i-Y
~ -------------------------------------------------------------
BUCHENJEGELE 112 239.2 5465 95555
BUDUSHI 289 93.66 5355 94705
~ BUGEMBE 281 272.1 5085 94845
BUHEKELA 135 279.0 5755 94735
BUKAMA 67.00 6.2998E-03! 5905 95375
~ BUKEHE 265 239.4 4875 95315
BUKOKO 54.00 375.8 5785 95175
\ BULAMBUKA 241 94.69 4995 95655
~ .! " BULEHYA 69.00 130.3 5825 95415
BULUMBELA 101 376.1 5485 95375
BULUNDE 203 279.3 4965 95245
~ BULYANG 60.00 375.4 5725 95295
BUL \'ANGAM I UI 100 375.9 5405 95415
BUSOI1EKE 123 102.7 5505 95005
~ I BUSOHDO 280 272.8 5185 94795
1 BUTAHDULA 227 279.0 5145 95395
CHABUHJA 217 94.69 4705 93695
• ! CHABUHIA 294 272.8 5385 94805
CHAMINHWA 248 94.69 4895 95465
CHAMIPULU 234 239.2 5075 95505
~ CHAMWABO 252 239.4 4985 95365
CHAPELA l2B 102.7 5535 94925
CHEKELENI 324 96 .43 4185 94385
• CHESA 13.00 103.3 4375 94565
CHIBISO 96.00 74.15 5375' 95645
! CHOMACHAfII(OL 97.00 92.08 5405 95575
• GOWEKO 168 272.4 5145 94115
GULUf1UNI 221 375.9 5395 95415
HINDISHI 68.00 6.2998E-03! 6085 95445
-; rBAM B 0 329 376.0 4355 94675
! IBELAMILUNDI 44.00 272.4 5205 94685
U30J A 242 94.69 4935 95655
• IBOLE 88.00 374.9 5865 95635
IBOLOGERO 103 376.1 5515 95305
I B US HI 296 272.3 5255 94935
-I IBUTAMISUZI 61 .00 6.2998E-03! 6055 95385
ICHEMBA 330 279.3 4275 94735
IDITIMA 276 279.3 4725 95325
• , IDUBULA ! 258 279.2 4975 95295
IF UNB A 228 93.66 5255 95545
lFUTA 317 272.4 3695 94245
~ , IGAlULA 166 103.3 5005 94195
.1 IGALULA 209 272.8 5075 95455
IGIGWA 189 279.2 4735 . 94065
-rGOGO 51. 00 272.8 . ! 5805 95235
[GOKO 40.00 103.3 5105 94665
IGOl1BE 20.00 279.3 4735 94705
• IGOWELO 134 278.9 5645 94765
IGUMO 130 376.1 5485 94935
IGUflGA 77.00 6.2998E-03! 5965 95255
• rGURUBI 90.00 374.9 5795 95635
IGWISr 334 96 .43 3765 94555
IJANIJA 197 279.2 5155 95355
• -------------------------------------------------------------
• ......
A 6.1-2
CEEP BOREHOLE POTENTIAL
'ilL tlF' YIELD U TM- X UTM-Y ---.-------------------------------_.------------------------_.-
1,.1 Or...lOHYA 65. DO I G. 2998E-03! 5945 95465
IKIhDWii 263 94 .69 4895 95445
IKOfiGOLO 28.00 103.3 4885 94(;·65
~1<:lI(IGU- IF'! NA 1010 102.7 5375 95 ! 15
:LriGr-'j,JA 235 93.66 5085 95545
;. L i'lL 0 206 97.10 4875 95625
ILALlH,HSINBA 159 103.3 5105 94575
:LELAI1HINHA 301 273. 0 5045 94<· 45
ILOLANGULU 1 .000 103.3 4585 94375
nlALAKAS'EKO 215 279. 2 5135 94205
ll'1ALAMAKOYE 305 272. " 3985 943',.5
IMALAlllHAYO 26.00 279.3 4845 94525
11'( A 1_ A H 1 HA Y I] 335 96.43 3725 94465
U'lALAI1PAKA 47 00 103. -, 5095 '34505 v' .J
r N ALiHIG UZ Jj 78. 00 <;. 2998E-03! 5875 95435
UiALAU[)UK I 1 9 . 00 103. 3 4425 94565
:i-1ALILO 104 74. l5 5505 95475
,NAGANA 302 103. ., 5095 9469.5
r N Al A 200 279. 1 4895 94385
;POl.E 185 272. l:' 4695 93585
rpULULU It,? 103. ., 4925 94185
~FUf'l8UL I 151 77'"' 0 5075 95205 -" ".
IPur'1BUL'y'A 52.00 , 6 2998E-l).3! 5855 95205
:SAGENHE 230 93.66 5255 95535
ISAGEHHE 260 1 I):;. :3 4885 9.5205
: S Af'.. A f1A L r ~,.I A -~ 00 1 149 6145 95515 , co·
:SAlALO 1 4-1 376. , 5215 '33195
I'2,tUiZU 1 <'1-, .-. .., ,." 8 5105 952~,5 L'f.:. -c: / .::.
r',EHEGE.JH l21 376. 1 5475 94993
ISEt'U:;A ,.000 279.3 4605 94305
I~;ERAt1AGHZr 77'> 1 I) 2. 7 4095 94905 '.' '.J~
, ISHIKI 140 279. 0 5095 95145
ISH I L H1ULWA 157 27'3.3 4485 95135
It'IF. I ZYA .39.00 103. 3 5105 94635
:~'!L.A 3.000 2'79.:3 4525 94385
ro If'iU-K IRUrlG l tB. 00 279 4495 94605
,SONGI»A 321 96.43 ! 4135 94225
,SUGILO 64. 00 6.2998E-03! 5945 95295
rSIJrlltA .j 00 2"? 9. . 1 5165 94715 .:. '-'I!.
,T AG A 22.00 103. :] 4715 94545
:TALE ·63. '00 374.9 5615 95235
[TECAMATIJI 356. 9 (\ .43 4215 94315
:TETEI1IA 160 11)3 ., 4755 94385 'J
IT ILl) 148 279, 2 5185 95295
:TIPKA t1.00 2 'j" 2 , 4 4325 94435
:rOBO 250 239. 4 4985 95375
; TOtiJ «rlDA -~ 00 279. ::; 4905 94485 .:, {
r T UL U 161 279.2 4855 94305
fT!.JNDA 257 279, 3 4965 95255
:TIJfWU A 312 272. 9 4065 94375
ITUfiDU 8 355 272, 9 4065 94375
ITlJrlDURU 82.00 1 160 5705 95405
,YOGELO 76,00 .3?4. 'J 6095 95555
... .1
.1
----------------------------------------------_._-------------
A 6.1-3
C'EEP BOREHOLE POTENTIAL
! NAME VIL HR Y JELD UTM-X UTM-Y ------------------------------------------------------------
. ! .. nOMBO 143 376.1 5115 95255
1. IZEHGABATOGI 369 96 .43 4185 94185
IZIHBILI 57.00 279 4665 94485
-.! .. liIHBILI 212 96 .43 4335 94235
! J I OH E EH WE N YE 309 102.7 4125 94665
KABALE 233 93.66 5165 95545
KABILA 24.00 279.3 4745 94625 .
d. KABUHBU 117 239.9 5695 95175
. KAGOHGIdA 89.00 1.179 5745 95515
1. KAGONGIdA 253 272.8 5115 95365
[ KAHAHA YA HH 274 279.1 4775 95375
KAKOLA 25.00 279.3 4795 94615
! KAKULUNGU 298 ! 103.3 4975 94685
! .. KALANGALE 85.00 79.24 5715 95585
. KALEHBELA 362 272.6 4205 94415
KALEHELA A 308 238.4 3955 94405
.! KALEMELA B 357 96 .43 3945 94455
KALEHELA 127 376.1 5475 94995
! .. KALI UA 343 272.6 3685 94395
KALOLA 9.000 94 .69 4445 94455·
. KALOLEH I 300 279.1 5045 94715
KALUMWA 31. 00 279.3 4845 94605
KALUNDE 59.00 279 4665 94485
KAMPALA 286 272.8 5245 94735
L KAMSEKWA A 345 96.43 3565 94545
KAMSEKWA B 348 96.43 3605 94515
KANGEH£ 340 323.1 3435 94015
KA HO G E 365 279.3 4265 94705
1. KAHYEHY£ 32.00 103.3 4855 94665
I(APILULA 314 272.9 3985 94365
KAS£LA 255 94.69 4995 95465
! KASENGA 33.00 279.3 4905 94575
KASHISHI 366 272.1 4325 l 95175
KA S I SI 164 102.4 4695 ! 94255
I(ASISI 313 272.9 4015 94355
KATEGIL£ 17.00 103.3 4535 94565
KATUHGURU 325 238.9 4115 94315
KAYOMBO 264 103.3 4845 95405
KAZAROHO 211 96 .43 3725 9452'
KAZIMA 45.00 279.1 4835 94485
KIDALU 73.00 6.2998£-03! 6145 95415
KIDETE 358 279.3 4955 95255
I KIGANDU 283 279.3 5065 94815
KIGWA 41.00 279. 1 5015 94415
K I GWA 170 103.3 5145 94335
KIKOHOKA 269 272.4 4645 94955
I UKUHGU 183 94.69 4735 93685
ULABILI 232 93.66 5115 95505
I KILItlO 275 279.1 4785 95365 , KILOLELI 181 238.7 4995 !. 93485
KILOLEHI 328 272.6 4255 ! 94435 , I(I LOLI 216 82.33 5475 92415
I(I LUHBI 195 237.8 5225 92975 ._----------------------------------------------------------
A 6.1-4
C[EP BOREHOLE POTENTIAL
rl A M E I'lL rlR 'fIEL[) UTM -X UT M'- Y
-------------------------------------------------------------UHAMAGI 16.3 2;"3.1 5045 94365
, UHHI,IA 363 2('2.6 4295 94455
i(!rIIHG 75.00 3'?4.9 6035 95615
UHUHGU 91.00 79.24 5575 95605
UPANGA 180 94.69 4805 93675
n PUNGULU 353 100.2 52S5 95035
n SAI1GA 179' 376.1 4815 93845
U SENGl 171 272.8 5645 94095
KISHILl 247 94.69 4905 95435
nTANGIL! 1 15 279. I] 5475 95205
UTAHGlLI 224 376. 1 52 S5 95365 ,
f( I TEHGbJE 222 279.2 5295 95315
KOrt8E 350 239.8 3365 94425
LAKUY I ..... 1:" 1 272.8 5075 95425 <.", , LOYA 1 .,. .-;. 278.5 5895 94445
,~
lUGUBIJ 47.00 279 5935 94975
LIJ118UlA 336 272.4 3625 94335
LUHGIJYA 35.00 103.3 4965 94585
LU TEIJ[)E 175 375.9 5795 942 '?5
LYM1ALAGWA ''"17("< 74.15 5045 9.5605 f'_ ..JO
'·1 A BA M A 6.000 94.69 4455 94335
I,ABiSILO 287 93.66 5235 94815
r'lABOHA 351 9'') 7-' 3075 94215 <:... • -...J (
!'lABON[)ULU .3 26 96.43 4165 94475
IHiGE N GA TI 297 279.0 5045 94645
!'IAG!R! 42.00 103 . .3 5055 94545
rH ... GO B A- TU R A 1 '? i '36.11 5935 93925
HAGOWEKO 23.00 279.3 4765 94635
! !-iAGU!(ULA 304 2? 2. 1 4945 94805
['1 A HE N E 249 94.69 4855 95525
NA \,J E r~ GO 29.01] 279.3 4925 94605
I-IA,.IENGO 1 .,. .:, .3 76.1 5485 94915
HA,rOJ ORO 193 237.8 5225 92975
riAKINGl 331 279.3 4215 94795
IH1LILITA 98.00 93.66 5355 . 954,,5
! t1..LOLO 262 272.8 4845 95455
tlALO rl CI,.I E 173 279. 1 5705 94005
t'lAI'1BAL! 268 279.0 4645 95005
NANGA':;HINI 295 2'1'2. S 5385 94805
l'IANGUflGIJ 53.00 375,8 5725 95145
1·1 A Sf, G ill A 27.00 279. 1 4795 94545
J nATlN,JE [ 13 27'2.8 5505 95545
!-lA \'0 1'1 80 38.00 103.3 4995 94515
HBIlG 1,.1 A 27'~ 94.69 5095 94945
1181T I \' A IJ PU 36.00 103.3 4935 94., 55
!1B I r r 8,000 2'1'9,3 4465 94465
! QSOGA 27'.3 279.3 4615 95245
nSOGWE 1 98 .375.2 5305 95425
!-!BOLA 4.000 279.3 4555 94465
!'18!JTU 56.00 J 6.2998E-03! 5985 953.)5
f'IGAMBO 214 80.28 5295 92445
liGONGORO 46.00 89.78 6075 95215
nHEf18E 150 279."3 4985 95255 -------------_._--------_._-------------_._-----------_._--------
I
A 6.1-5
[EEP BOREHOLE POTENTIAL
t\A M E 'lIl HR YIELD UTM -X UTM-V
-------------------------------------------------------------1'iH Of; 0 lA i1H Ul I DEL'E fll GONG,JA IHGUNGUNALO
,i IHGULJA i IlIRAM80 I TOB
Ii I SH A '" fllZANZA
t1!(OlYE I'IOGLJA 110LE MONDO 110TOMOTO t1GYOFUKE I'IP DG 0 LO I'IP O!~ 8 (,.lE MTAKUJA t1TAKU,IA t1lJHUG r !11J Uf! G AH 0 !!I;iA8 A K I i'IA t'lUf.l8AF:RTGRU t'll .. ] AE: U BE LE li~!AGALA
liB ilG U CU L I i1 tJ A J I L U ~l G A t1fJ AV H '3H Af! H AL r'!!.J HL A L~-! i'!!:! Al U ZW I L 0 l'tU AM A KO flFi :'l',JM1AlA !i'A Ml A LA t,! i) A NAP U L I ~.~~;.I Ar-! A '3H I G A nUHMASHIt1B~\
l~I.'J RH ~ AH A lii.:flM L OL 1 I~UAHDIHINIJ;: \ ~I~J At~ H AL A i,'-!l:JAHYAGULA W.:JAHZOl I HIJAt12UG I ,-i',; AI~ Z IJ I lO !~';J~'::{iLA
)~l;j~l:;H If~:U
;~fJ A(:.! T Lt! ~<H.1AZ I zr tlt..1 Ell G E t1HEflG£M8UTU 11h.J.ISOLO !'1!.·} OH G 02 1]
!'i:lfi~lZ:BA
H!itlG A
229-158 70.00 1 <; . 00 201 303 21. 00 124 l78 267 1 ~ i 95.00 359 118 132 219 182 346 145 310 66,00 1 11 :33,00 81 00 236 93.00 285 .q. 9.00 207 79.01) 12r; 245 92.00 71.00 80.00
139 87.00 :36 00 138 74.00 223 48.00 240 99.DO 94,00
116 192 2 '70 1.74 267 354 1 10
S13 . 66 279.3 130.3 103,3 376, 1 103.3 27 <;), 1 279.2 94,69 279 _ 1 103,3 74,15 96,43 375,4 279.2 103,3 272. 1 %,43 102,7 96.43
6. 2998E"03! 240.3 98.70 132.4 93.G6 132.4 94.69 374.8 -:13.66
I 6, ~:998E-03 I
102.7 94.69 272,8 1 512
I. 6.2998£-'02,1 102 7 126. 6 79.24 3 ? {; "1
6.2998£-03 ! 102. l ! 127.2 94.69 74_15 74 15 102 .. ? 98.70 82.02 103.3 1 0 1 5 376.0 279.0 375.4
5275 4495 5825 4475 5305 4875 4715 5585 4665 4865 4605 5445 3865 5615 5635 4665 4885 3485 5225 4045 5975 5715 5585 5775 5015 5715 5145 6055 5255 5825 5645 493.5
·5555 5825 5905
5175 5615 5685 5175 6015 5325 5975 4755 5335 5535 5525 5745 5225 4745 5365 4355 5225 5695
35465 95205 95415 94525 95355 94705 94595 95015 93B55 95285 93985 '15655 94405 95215 94925 94075
.93535 94555 95145 94445 95385 93365 '15345 95545 95525 9%85 94805 9·5045 95535 95505 95015 95475 95535 95405 '35475
9509~5
95495 955'~5
95165 95455 95275 9.s1~:,5
95635 95635 956(,5 949'35 95225 92445 95155 94235 94675 95005 95275
-------------------------------------------------------------
A 6,1-6
PEEP EOREHOLE POTENTIAL
\Ill NR 'i IELP UTt1-X UTl1-Y
-------------------------------------------------------------
r!ATA ~-, 93.66 5135 95535 .::. .;J !
,lfHJF, 24(, 97. 1 0 4865 95605
r!Co Et. E Ll 291 93.66 5295 94825
flDEt1BEZ I 107 376.0 5435 95205
[I i) E \I E UJ A 162 103. 3 4B65 94365
HDOflO 10.01) 239. 4 4405 94355
tlG UK U NI] 208 279. 2 5175 95015
riG UL U 105 376. 1 54B5 95375
tlGUF:ITI i 25 99.51 5655 95125
tlG IJ\-' ij tlO·J A 50.01] 127.2 5975 95165
,-IHA8ALA 277 103.3 4655 954:35
rll Nr'l] ! . 25f. 94.69 4995 955;25
tlK HIGA 1 1 " 376. 1 5455 95105
NK It'1G(~ 292 Cl .... ,.. ... 5395 94905 .".j • lob
elK 11'1 I ZI IHi 278 279,0 5165 94915
twonno 31G 96.43 3795 94365
rH: ULtJ S I 12.01] 94.69 4355 94455
rISEr/DR KA 1'1 or:; 1 .307 96.43 3975 94285
tiSOGOLO 3,64 % .43 4225 94175
W:,OLOLO 16::1 100.10 5105 94055
lIS Ut'l B fl 2 -" 279,3 4615 95225 , ~ tiS Uj-j G lMA 318 239.8 3B55 95035
tlTALIKfJA 153 103. 3 4695 94355
I1 T r C U ~ 1 ,. 272. 8 5515 95235 , ,.,
tlT080 84.00 279 5545 95355
tl'i Atl G I<H E 15!;; 279. 7 4515 9.5145 .J
tlZ UB IJ KA 154 103. 3 4785 94723
W:UG I 11LOLE 1 94 10 1 . 0 5985 '331>35
tlZ UG I 11L OL E 339 92.37 3455 94035
PO Z>Hl OY 0 :3 3."3 272 . .. 3635 94345 I,
SAGIDA ..., ......... 272.8 5045 95455 c... ,j {
::;Ei1E t18E LA 271 279.3 4615 95225
SH EL L A 352 93.66 3135 94215
SH IC(1I18FI 202 93.G6 5065 95345
SH !TAGE 155 279.3 4495 95175
SlG!LI 243 94.69 4945 95675
:::IKONGE 1~ry 272. 1 4735 93815 , {
SlLIMUVA 149 279,2 5215 95315
Slf'18 0 < 7- :~76 . 1 5485 94845 i. '-' {
:30,JO 239 99.18 4805 95625
SO riG A 1'18 EL E 205 272,4 3925 94895
SOtlGM18ELE 213 272. 9 3995 94 iO 15
~~ U t~ et bJ I Z I 120 279. ., 5565 95085 ~
'AI'18AUlLE 131 102. ry 5575 94835 , TU NB I 2.000 103. 3 4655 94395
7U N8 I 2'33 93.66 5335 94905
,U~IB I Ll 188 279.0 4755 93995
':-U0118E MUNGU 1 3.38 238.9 3515 94365
'iU TU 0 187 103.3 4635 93935
U8INGA 147 102. '? 5335 95135
UCHJOtf1A 19€, 279.2 5'185 95385
UDOfiGO i ::34 239.4 4685 93623
UOULA 261 271.8 4925 95345
----------------------_._--------------------------------------
A6.1-7
~EEP 80REHOlE POTENTIAL
\' IEll) UTM-X UTM-\' NAME V IL HR
-----------------------------------------------------------4935 4315 5545 4285 3605 5245 3835 3865 2975 3345 3145 6025 5445 5735 5305 4935 5205 4715 5165 4795 4655 4135 4885 3755 3685 3105 4275 4255 5505 4915 5525 4775 54'35 4495 5185 3895 4845 3805 33<;15 5315 4805 5305 5425 5165 4935
95405 94495 95165 94465 94385 94735 94965 94335 93655 93905 93735 94425 95145 95425 95245 94565 94755 94465 94715 95345 94215 94325 95375 94445 94385 94355 94295 94395 95255 93715 94825 93395 94785 94285 95175 94575 94565 94395 94535 95415 95625 94755 95295 95465 95225
UDUTU UFULUMA UGAKA
, UGO~fOlA
UGUflGA UHEMELI
I UHIMDI lJK OMDAMO\'O UKUMB I 107 IJKUMB I-SI GAfI UKUMB I-SI GAfI UlASA 8
i UlA'I'A , UHI)OMO
UPINA ! fJPUGE
UPUNGU URAMBA
I USAGALI USALAlA US ES U LA USISYA USOflGWANHAlA ! USSIMBA UfDO ! USSIMI)! USSINGE USSOKE 11LIMA
, USSOKE USSONGO USlJUGA US WAY A UT H1UlE UTUJ A IHUlA UTIJIGU iJ',' 0 G I] UY U I \·'UMlUfl A )ACHA~!ASEME
UE LA \JELfi AITA ::18A :0 GO L 0 ~UGlMLI]LE
254 15.00 109 14.00 337 288 319 210 342 341 360 306 108 226 146 34.00 284 58.00 299 266 190 323 204 361 344 349 320 327 62.00 212 133 186 13<; 5.000 141 311 30.00 ~15 347 1 9~} 244 220 102 225 259
94.69 96.43 272.8 272.6 %.43 272.8 %.43 %.43 107.4 92.37 92.37
O. 0000 374.9
6.2998£-03! 102.7 279.3 278.5 103.3 279.1 271.8 272.1 96.43 103.3 96.43 272.6 <;16.43 272.9 272.9 279.2 374.9 272.8 94.69 376. i 94.69 376. i 272.4 279.2 96.4:3 96.43 375.2 9 Si. 18 272.8 376.0 279.2 279.3
APPENDIX 6.2
RESULT OF SHALLOW WELL INVENTORY
::istr~c:: NZEGA
Serial ,ell ~o. Location ur~ ~epth S.~!. L Q~ t~ Dynam i c tR 110 Geological formation, Land class, , .)
No. m/m in m in Ha ter rli n m..!/min Aquifers and Remarks Level (t~)
Deep residual soil horizon. Deep 5263 94737 8 4:2029 Ndala 4.80 1.85 0.40 4 3.85 200 0.008 soils, silty sand to sand. viater
is available throughout the year, but construction is not perfect. Deep residual soil horizon.Laterite.
12 4:2040 Zogoro 5175 94455 5.20 3.40 0.35 5 5.03 140 0.012 Deep soils, silty sand and 1aterite. Water is available throughout the year, slightly saline. Deen residual soil horizon. Laterite.
13 4:2044 ~1wangoye 5095 95524 14.00 6.80 0.37 4 7.40 170 0.008 Deep soils, silty sand and laterite.
Water is available throughout the year. Deep residual soil horizon. Deep
14 4:2055 Mwamala 4944 95486 6.10 soils. Si1ty sand and laterite.
7.40 0.40 4 7.07 150 0.010 I-iater is available throughout the ;ro,
year but very little amount during '" the dry oeri od . N I
Granite(Shallow residual soil ~
11 4:2037 Miguwa 5335 95 350 1. 04 1. 81 cover). Shallow soils, silty sand.
2.80 0.40 1. 75 65 0.011 Water is available throughout the year but little turbid. Depth could be increased. Shallow residual soild horizon.
5291 95409 Shallow SOils. Silty sand to sand.
9 4:2039 Mbogwe 2.60 0.80 0.40 2 1. 30 60 0.013 Water is available throughout the year. It is situated within the seeeage line. Granite(Shallow residual soil
5267 95345 cover) Shallow soils. Silty sand
10 4:2036 Kitangil i 2.65 0.85 0.40 2 1. 35 180 0.0044 to sand and weathered granite. Very little amount of water during the qry months. Depth could be 1 ncreased. Alluvium(Filled Valley) Alluvial
4810~5640 Deposits. Si Hy sand to sand.
15 4:2056 Igusu1e 3.30 0.91 0.40 10 1. 35 60 0.057 Water is available throughout the year. Very potential shallow well.
~tr' "UNr
Serial Well No. Location UTI~ Depth S. vi. L Q3/. tp Dynamic tR Q3 Geological formation, Land class, No. m mln min ~ater min m /min Aquifers and Remarks
Level un Granite(shallow residual soil coveD
5450 95317 Shallow soils, silty clay to fine
6 4:2017 Zi ba 3.30 l. 36 0.40 3 2.26 165 0.007 sand. Water is not available during the dry months. Depth could be inc~ eased. Granite(Shallow residual soil coveD
7 ~: 2021 Ibologelo 5543 95 327 7.10 0.65 0.40 4.13 2.24 210 0.008 Silty clay to fine sand. viater is available throughout the year but slightly saline. Granite(Shallow residual soil coveD
5 4:2013 Ndembezi 5463 95208 3.63 l. 36 0.40 Shallow soils. Silty sand and
2 l.66 50 0.015 . weathered granite. Quantity of water is very little during the dry months.Depth could be increased. Granite(Shallow residual soild cov- ~ er)Shallow soild. Silty sand to· m
5502 94942 sand. Water is avialable through- N
2 4:2006 Igumo 2.92 l. 43 0.40 4 2.03 60 0.025 out the year, but very little r N
quantity during the dry months (October to December) Depth could be increased. Alluvium(Filled Valley).Alluvial
3 4:2009 1·1wi s i 5499 95002 5.20 4.32 0.40 12 4.90 200 0.023 Deposits. Silty clay to sand. Water is available throughout; the year Alluvium(Filled Valley). Alluvial
4:2001 Simbo 5483 94868 2.53 l. 28 0.40 4 2.28 90 0.017 Deposits. Clay and Sand. Tuxbid water is available thro~ghout the year. Depth could be increased. Alluvium(Filled Valley). Alluvial
4 4: 2011 Mwisi 5500 94997 4.87 2.30 0.24 8 2.74 105 0.016 Deposits. Silty clay to sand. Water is avialable throughout the year.
-'~"""'0'_.-.~ __ -, ."~.~,..,.~"..ftt'.~y,, } JURi, i '.~'
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Serial A'ell ~o. Location ur~ Depth S. ;'!. L OR/ tfJ Dynami c tR 03 Geological formation, Land class, ~o. mO min m'in Water min :n /min Aquifers and Remarks
Level (m)
Filled Va11eY1A11uvium)A11uvia1 I';;
~
20 4:2082 Ussoke 4260 94 350 Deposits .. Si ty sand to sand.
6.21 2.90 0.40 45 3.66 190 0.076 Water is avialable throughout the Rly. Stn. year. Very potential well.Fitted
with a diesel eump. Deep residual soil horizon.
17 4:2072 Ka 1 i ua 3663 94410 5.28 4.00 0.20 5 5.05 93 0.010 (Laterite). Deep soils.Silty sand and laterite.Water is available throughout the year. Deep residual soil(Laterite)
3500 94 552 16 4:2071 Igagala 6.25 3.42 0.40 7 6.15 167 0.016 Horiszon.Deep soi1s.Si1ty sand and 1aterite.Water is available throughout the year. Deep residual soil horizon.
21 4:413 Kazaroho 3722 94496 6.84 5.92 0.25 8 6.83 120 0.016 (Laterite). Deep soils. Si1ty sand »> and 1aterite. Water is available en throughout the year. N
I
Deep residual soil horizon. w
23 4:415 Igwisi 3760 94545 7.07 5.02 0.32 10 6.86 215 0.014 (Laterite).Deep soils,silty sand arid 1aterite. Water is available throughout the year. Deep residual soil horizon.
22 4:414 Ka1eme1a 3955 94438 6.45 .5.93 0.37 7 6.40 ,280 0.009 (llaterite)Deep sOils,silty sand and 1aterite.Litt1e water during the dry months. Deep residual soil horizon.
18 4:2073 Urambo 3965 94400 6.90 4.50 0.26 12 6.40 158 0.020 (Laterite) Deep soils,si1ty sand Town and 1aterite.Water is available
throughout the year. Deep residual soil horizon.
24 4:416 Itundu 4065 94380 4.50 3.32 0.40 7 4.44 142 0.020 (Laterite) Deep soils, si1ty sand and 1aterite. Water is available throughout the year.
41~0 943M ' Filled ValleY(Alluvium) Alluvial
19 4:2078 Chekeleni 1.96 O.S2 0.34 n 1. 73 66 0.019 Deposits.Silty clay to fine sand. .., Water is available throughout the
(.'"-.~-'
.I'~ilL. Del?t.h.cou ld be increased.
·~---~ .. ---- .-,"-.~
S eri a ~ ',\'r.?11 No. Location UTII, Depth S. ~:. L or; / t "f-;,l Q9, Geological formation, Land c1 ass, Oynami c " , \0. ,) . n
~n~J/m'i'1 '1' mln min ~ia ter :l:~ n Aquifers and Remarks Level(m)
4660 94390 Filled Valley(Alluvium)Alluvial
25 4:2086 Tumbi 3.55 2.07 0.32 5 3.30 60 0.025 deposits,silty clay to sand.Water is available throughout the year. Deep residual soil horizon. Deep
30 4:2102 Igalu1a 5013 94216 A.56 0.93 0.40 41 1. 40 209 0.066 soil,silty sand to sand.Water is
Rly.Stn. available throughout the year. Fitted with a diesel pump. Filled val1ey(Alluvium) Alluvial
4970 94 560 deposits. Clay to silty clay. Very
28 4: 2093 Upuge 4.00 1. 22 0.40 9 3.85 321 0.011 turbid water. Water is available throughout the year.Solid rings without fi Her. Granite(Shallow residual soil
4770 94370 cover)Shallow soils,sandy clay
27 4:2089 Kipalapala 4.00 2.72 0.45 9 3.86 160 0.024 to fine sand and laterite at the p Mission bottom. Water is available through- CS>
out the year. . N
Deep residual soil horizon. I
.",
Sikonge 4715 93 795 (Laterite) Deep soils,silty sand 32 4: 2112 (Birani 6.20 4.08 0.39 7 6.00 246 0.011
PrimarySc) and laterite.Water is available throughout the year. Deep residual soil horizon.
31 4: 2109 Mko lye 4671 93865 4.65 3.75 0.39 7 4.48 277 0.010 (Laterite)Leep soils,silty sand and leterite.Water is available throughout the year. Granite(Shallow residual soil
29 4:2094 Upuge 4968 94 550 4.00 3.08 0.40 2.6 3.68 80 0.013 cover. Shallow soils,silty sand and laterite.Water is available throughout the year. Granite(Shallow residual soil
33 4:419 Igalula 5115 94585 3.80 2.85 0.40 4.3 3.30 60 0.027 cover,laterite)Shallow soils. silty sand and laterite.Very little amount of water during the dry mths Granite(Shallow residual soil
4733 94 S43 cover)Shallow soils,silty sand to
<:'b 4: LUts7 I-caga 7.45 2.40 0.40 61 5.46 sand. Recovery is very poor 0.02m has recovered after 120 mins. It
J is a very old wel1.~1ight have been sealed.
