11
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road HYDROLOGICAL STUDY REPORT FOR THE CONSTRUCTION OF BRIDGE AT –4/1 WELIGAMA – TELIJJAWILA B466 ROAD 107 – DENIPITIYA BRIDGE
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road
HYDROLOGICAL STUDY REPORT FOR THE CONSTRUCTION OF BRIDGE AT –4/1 WELIGAMA – TELIJJAWILA B466 ROAD
107 – DENIPITIYA BRIDGE
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road
TABLE OF CONTENTS
1 Introduction ......................................................................................................................... 3
2 Methodology of the Assessment ........................................................................................... 3
2.1 Salient Steps ........................................................................................................................................ 3
2.2 Assimilation of Topographic and Hydrological Data ..................................................................... 3
2.2.1 Topographic Data for Catchment Delineation ................................................................................. 3
2.2.2 Hydrologic Data .............................................................................................................................. 3
2.3 Rainfall Intensity Duration Frequency (IDF) Curves ..................................................................... 4
2.4 Intensive Site Reconnaissance Survey for Understanding Prevailing Drainage Issues ............ 5
2.5 Hydrologic and Hydraulic Computations – Capacity Adequacy Checks ...................................... 6
2.6 Hydrologic Design .............................................................................................................................. 6
2.6.1 General ........................................................................................................................................... 6
3 Conclusions and Recommendations .................................................................................. 11
3.1 Conclusions ....................................................................................................................................... 11
3.2 Recommendations ............................................................................................................................ 11
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road HYDROLOGICAL STUDY FOR BRIDGE NO 4/1 WELIGAMA – TELIJJAWILA B466 ROAD
1 Introduction
This report hydrological and hydraulic analysis which was carried out after site reconnaissance. It provides recommendations for the proposed opening sizes for the bridge at Weligama – Telijjawila B466 Road.
The main stream is the Polwatte Ganga.
2 Methodology of the Assessment
2.1 Salient Steps The proposed methodology for the drainage assessment consists of the following steps.
(1) Assimilation of all relevant topographic and hydrologic data relevant to the roads drainage. i.e. 1:50,000 digital maps of Survey Department were mainly used in a GIS base along with Google Earth satellite imagery.
(2) Site reconnaissance and understanding the prevailing drainage and scour issues especially around the candidate bridge.
(3) Hydrologic and hydraulic computations to ascertain the capacity adequacy of the candidate bridge
(4) Conclusions regarding the structure capacity in terms of the present and proposed opening sizes/cross section, scour depth etc.
2.2 Assimilation of Topographic and Hydrological Data
2.2.1 Topographic Data for Catchment Delineation Digital maps with 1:50,000 scale was used to locate the bridge catchment areas as these maps are accurate and user friendly while gathering information related the catchment. Bridge location was obtained through GPS coordinates and the locations were transmitted to a GIS database (Arc Maps).
2.2.2 Hydrologic Data The main hydrologic data required for the hydrological and hydraulic assessments apart from the topographic information are;
Rainfall Intensity Duration Frequency Curves (IDF Curves) for different road stretches
Time of concentration
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road Figure 1-Location Map of Bridge No 4/1Weligama – Telijjawila B466 Road
2.3 Rainfall Intensity Duration Frequency (IDF) Curves
Rainfall and Intensity Duration Frequency [IDF] Curves were obtained from the research paper Entitled “Towards More Efficient Hydraulic and Hydrological Design of Cross Drainage Structures Using New Developed Intensity Duration Frequency Equations” by D G L Ranathunge. This paper has presented IDF curves for many localities throughout the country where pluviograph rainfall data are present (mainly the principal met stations manned by the Department Meteorology and selected other stations manned by the Department of irrigation).These IDF curves equations serve as secondary data derived from primary rainfall data obtained from the Department of Meteorology and Department of Irrigation etc. IDF curves for Galle was used for the calculations as this is the closest meteorological stations with IDF information.
Figure 2-Hydrological Stations and Zones – Sri Lanka
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road The IDF data relevant to this project are collected and presented below.
Figure 3- Rainfall Intensity Duration Frequency Curves (IDF Curves)
2.4 Intensive Site Reconnaissance Survey for Understanding Prevailing Drainage Issues
Drainage issues were identified during a site visit on 21st March 2014. The relevant stakeholders close to the bridge were met and their views were obtained to assess the prevailing flooding issues. The Bridge in consideration has the following observations.
1. The Downstream connect with the sea about 3 km distance. 2. Down stream Polwaththa and upstream Koledanda bridges are on the same river.
Figure 4- Location Map and Important details for the Hydrological Analysis
0
50
100
150
200
250
0 15 30 45 60 75 90 105 120 135 150
RAIN
FALL
INTE
NSI
TY -
MM
/HR
DURATION - MIN
R A I NFA LL I N T EN S I T Y D UR AT I O N F R EQU EN CY CU RVE S -GA L LE S TAT I ON
2yr 10yr 50yr 100yr
2yr: I= 1806*[t+35}^-0.7825710yr:I= 3861*[t+48]^-0.8279850yr:I= 5933*[t+55}^-0.84987100yr:I=6471*(t+55)^-0.84823
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road
3. Has never flooded according to the information received.
2.5 Hydrologic and Hydraulic Computations – Capacity Adequacy Checks Hydraulic computations were carried out to test the adequacy of the hydraulic structures using the SCS Formula for peak flow computations employing HEC HMS flood model software of US Corps of Engineers and Manning’s equations for hydraulic capacity computation using “Hydraulic Toolbox” software.
2.6 Hydrologic Design
2.6.1 General
The Hydrologic Calculation of the Denipitiya Bridge will be governed by the Hydrological condition of the Koledanda Bridge which is only 500m in the Upstream of the Polwatte Oya.
Therefore the Outflow of the Koledanda Bridge will be the inflow of Denipitiya Bridge,
Same Calculation of defining the peak flow for the Koledanda Bridge is used here (Considering the Flood Plain Effect)
For this calculation it is assumed that the water reaching the bridge at certain level starts to collect in the flood plain. In Koledanda bridge it is above 0.00mMSL elevation. And the rate of the water level increase is assumed 20mm per every 15 minutes at the peak discharge time.
To find the Peak Discharge Itterative method used with the help of Hydraulic Tool Box software and is presented below.
DENIPITIYA BRIDGE80°27'5.1"E, 5°58'55.6"N
Koggala Lake
Digili Ela
Nilwala Ganga
Nilwala Ganga
Polwatta Ganga
Polwatta Ganga
Urala Ela
Boralu Wewa
Hiyare Reservoir
Udugan Oya
Hulandawa Ganga
Polwatta Ganga
Digili Ela
Holuwagoda Ela
Moramba Wewa
Haliela Wewa
Maha Dola
Gin Ganga
Mamina Dola
Moramba Wewa
Udugan Oya
Badulla Oya
Udugan Oya
0
30.48
91.440002
60.959999
121.92
182.88
213.36 243.84
152.39999
182.88
243.84
213.36
91.440002
213.36
30.4
8
182.88
60.959999
182.88
30.48
30.48
213.36
91.440002
30.48
152.39999
91.440002 60.959999
30.48
60.959999
60.959999
121.92
60.959999
182.88
30.4
8
60.959999
152.39999
91.440002
121.92
30.4
8
121.92
30.4
8
60.959999
60.959999
60.959999
91.4
4000
2
182.
88
91.44000260.959999
30.48
30.48
60.95
9999
60.95999960.959999
182.
88
60.959999
91.440002
30.48
91.440002
91.440002 30.4
8
91.440002
60.959999
91.440002
30.48
121.92
121.92
121.92 121.92
30.48
30.48
91.4
4000
2
152.39999
121.92
213.36
182.88
30.48
30.48
30.48
30.48
60.959999
91.440002
91.440002
30.48
121.
92
30.48
60.95
9999
30.48
30.48
60.959999
30.48
60.959999
30.48
121.92
30.48
121.92
182.88
91.440002 121.92
60.959999
121.92
60.959999
243.84
121.92
30.48
121.92
30.48
182.88
30.48
30.48
60.959999
121.92
213.36
152.39999
60.959999
60.9599
99
30.48
30.48
121.92
30.48
30.48
121.92
60.959999
30.48
30.48
91.440002121.92
91.440002
30.48
30.48
30.48
121.92
30.48
121.92
121.92
121.92
60.95999960.959999
30.4
8
121.92
121.92
121.92152.39999
30.48
30.48
30.48
60.959999
152.39999
30.48
121.92
30.48
152.39999
121.92
121.92
30.48182.88
152.39999
30.48
60.959999
60.959999
91.440002
91.4
4000
2
60.959999
30.48
60.959999
30.48
91.440002
152.39999 60.9
5999
9
30.48
121.
92
30.48
30.48
121.92
60.95999960.959999
60.959999
152.
3999
9
30.48
60.959999
121.92
60.959999
30.4
8
121.92
213.36
60.959999
60.959999
30.48
30.48
121.92
30.48
182.88
60.959999
60.959999
30.4
8
60.959999
91.440002
30.48
60.959999
60.95
9999
91.44000230.48
30.48
60.959999
30.48
30.48
91.440002
30.48
121.
92
30.48
60.959999
30.48
182.88
30.48
LegendTE_Pt1
TE_LI1
HY_Hydro_Li
Catchment Area
HY_Hydro_Pg
<VALUE>-29.20285416 - 0
0 - 10.86860008
10.86860009 - 30.9043272
30.90432721 - 50.94005432
50.94005433 - 70.97578144
70.97578145 - 91.01150856
91.01150857 - 111.0472357
111.0472358 - 131.0829628
131.0829629 - 151.1186899
151.11869 - 171.154417
171.1544171 - 191.1901442
191.1901443 - 211.2258713
211.2258714 - 231.2615984
231.2615985 - 251.2973255
251.2973256 - 271.3330526
271.3330527 - 291.3687798
291.3687799 - 311.4045069
311.404507 - 331.440234
331.4402341 - 351.4759611
351.4759612 - 371.5116882
µ0 3,100 6,200 9,300 12,4001,550
Meters
Date Time IN Flow m3/sOut Flow m3/s
Discharge to the Flood Plain
Remarks
1-Jan-14 800 31-Jan-14 815 31-Jan-14 830 31-Jan-14 845 3.021-Jan-14 900 3.141-Jan-14 915 3.441-Jan-14 930 4.051-Jan-14 945 5.121-Jan-14 1000 6.881-Jan-14 1015 9.761-Jan-14 1030 14.281-Jan-14 1045 21.411-Jan-14 1100 34.931-Jan-14 1115 58.271-Jan-14 1130 90.441-Jan-14 1145 128.44 120.43 8.01 2.85 Depth1-Jan-14 1200 169.02 121.919 47.1011-Jan-14 1215 209.86 123.81 86.051-Jan-14 1230 249.85 125.716 124.1341-Jan-14 1245 288.47 127.637 160.8331-Jan-14 1300 325.46 129.524 195.9361-Jan-14 1315 360.85 131.526 229.3241-Jan-14 1330 394.73 133.493 261.2371-Jan-14 1345 427.32 135.475 291.8451-Jan-14 1400 458.86 137.472 321.3881-Jan-14 1415 489.17 139.485 349.6851-Jan-14 1430 517.84 141.513 376.3271-Jan-14 1445 544.85 143.557 401.2931-Jan-14 1500 570.37 145.616 424.7541-Jan-14 1515 594.57 147.69 446.881-Jan-14 1530 617.59 149.78 467.811-Jan-14 1545 639.52 151.885 487.6351-Jan-14 1600 660.43 154.006 506.4241-Jan-14 1615 680.31 156.142 524.1681-Jan-14 1630 699.08 158.294 540.7861-Jan-14 1645 716.56 160.462 556.0981-Jan-14 1700 732.38 732.381-Jan-14 1715 745.41 164.751 580.6591-Jan-14 1730 754.39 754.391-Jan-14 1745 758.8 168.826 589.9741-Jan-14 1800 769.18 769.181-Jan-14 1815 755.07 172.844 582.2261-Jan-14 1830 748.191-Jan-14 1845 738.71 176.558 562.1521-Jan-14 1900 727.081-Jan-14 1915 713.6 180.358 533.2421-Jan-14 1930 698.491-Jan-14 1945 681.91 184.248 497.6621-Jan-14 2000 663.911-Jan-14 2015 644.53 188.214 456.3161-Jan-14 2030 623.821-Jan-14 2045 601.88 192.272 409.6081-Jan-14 2100 578.721-Jan-14 2115 554.24 196.924 357.3161-Jan-14 2130 528.321-Jan-14 2145 500.74 201.984 298.7561-Jan-14 2200 471.271-Jan-14 2215 439.57 207.124 232.4461-Jan-14 2230 405.271-Jan-14 2245 367.82 203.862 163.9581-Jan-14 2300 326.281-Jan-14 2315 279.5 210.288 69.2121-Jan-14 2330 230.33 220.075 10.255 3.83 Depth1-Jan-14 2345 183.581-Jan-14 2400 138.51
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road Calculation of Backwater effect.
Sea level could rise to about 0.95m MSL in a combined extreme event with maximum spring tide (0.35m) wind set up (0.2m), wave set up (0.1m), cyclone 0.3m totaling to 0.95m
Backwater profiles along the main stream was calculated using the direct step method from a sea water level of 0.95 m MSL. M2 type backwater curves are found to exist along the streams towards the bridges. Simplified floodway parameters are assumed in the direct step method calculations. Backwater profiles and the design flood levels at the bridge is given in the Figure below.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 500 1000 1500 2000 2500 3000
Dep
th
Length
Backwater Curve Polwatte Oya
Denipitiya Bridge
Depth Area VelocityVelocity
headSpecific
headWetted
perimeterHydraulic
radiusFriction slope
Average slope
Specific head
differenceLength
incrementTotal
length(m) (m2) (m s-1) (m) (m) (m) (m) (m/m) (m/m) (m) (m) (m)
0 0.95 147.01 1.5 0.114 1.064 159.69 0.92 0.002252 - - - 04 0.955 147.84 1.49 0.113 1.068 159.74 0.93 0.002211 0.002216 0.001 0.8 3.28 0.96 148.67 1.48 0.112 1.072 159.79 0.93 0.002171 0.002176 0.001 0.8 6.512 0.966 149.5 1.47 0.11 1.076 159.85 0.94 0.002132 0.002137 0.001 0.9 9.916 0.971 150.33 1.46 0.109 1.08 159.9 0.94 0.002094 0.002099 0.001 0.9 13.520 0.976 151.16 1.46 0.108 1.084 159.95 0.95 0.002057 0.002062 0.001 0.9 17.224 0.981 151.99 1.45 0.107 1.088 160.01 0.95 0.002021 0.002025 0.001 1 21.128 0.986 152.82 1.44 0.106 1.092 160.06 0.95 0.001985 0.00199 0.001 1 25.132 0.992 153.65 1.43 0.105 1.096 160.11 0.96 0.001951 0.001955 0.001 1.1 29.336 0.997 154.48 1.42 0.103 1.1 160.17 0.96 0.001917 0.001921 0.001 1.1 33.740 1.002 155.31 1.42 0.102 1.104 160.22 0.97 0.001884 0.001888 0.001 1.2 38.244 1.007 156.15 1.41 0.101 1.108 160.27 0.97 0.001851 0.001855 0.001 1.2 4348 1.012 156.98 1.4 0.1 1.113 160.32 0.98 0.001819 0.001823 0.001 1.3 47.952 1.018 157.81 1.39 0.099 1.117 160.38 0.98 0.001788 0.001792 0.001 1.3 53.156 1.023 158.64 1.39 0.098 1.121 160.43 0.99 0.001758 0.001762 0.001 1.4 58.460 1.028 159.48 1.38 0.097 1.125 160.48 0.99 0.001728 0.001732 0.001 1.4 64.164 1.033 160.31 1.37 0.096 1.129 160.54 1 0.001699 0.001703 0.001 1.5 69.968 1.038 161.14 1.37 0.095 1.133 160.59 1 0.001671 0.001675 0.001 1.6 76.172 1.044 161.98 1.36 0.094 1.138 160.64 1.01 0.001643 0.001647 0.001 1.6 82.576 1.049 162.81 1.35 0.093 1.142 160.7 1.01 0.001616 0.001619 0.001 1.7 89.280 1.054 163.64 1.34 0.092 1.146 160.75 1.02 0.00159 0.001593 0.001 1.8 96.384 1.059 164.48 1.34 0.091 1.15 160.8 1.02 0.001563 0.001567 0.001 1.9 103.788 1.064 165.31 1.33 0.09 1.155 160.85 1.03 0.001538 0.001541 0.001 2 111.492 1.07 166.15 1.32 0.089 1.159 160.91 1.03 0.001513 0.001516 0.001 2.1 119.696 1.075 166.98 1.32 0.089 1.163 160.96 1.04 0.001489 0.001492 0.001 2.2 128.2100 1.08 167.82 1.31 0.088 1.168 161.01 1.04 0.001465 0.001468 0.001 2.3 137.3104 1.085 168.65 1.3 0.087 1.172 161.07 1.05 0.001441 0.001444 0.001 2.4 146.8108 1.09 169.49 1.3 0.086 1.176 161.12 1.05 0.001418 0.001421 0.001 2.6 156.9112 1.096 170.33 1.29 0.085 1.181 161.17 1.06 0.001396 0.001399 0.001 2.7 167.6116 1.101 171.16 1.29 0.084 1.185 161.22 1.06 0.001374 0.001377 0.001 2.9 179120 1.106 172 1.28 0.083 1.189 161.28 1.07 0.001352 0.001355 0.001 3.1 191.1124 1.111 172.84 1.27 0.083 1.194 161.33 1.07 0.001331 0.001334 0.001 3.3 203.9128 1.116 173.67 1.27 0.082 1.198 161.38 1.08 0.00131 0.001313 0.001 3.5 217.6132 1.121 174.51 1.26 0.081 1.203 161.44 1.08 0.00129 0.001293 0.001 3.8 232.3136 1.127 175.35 1.26 0.08 1.207 161.49 1.09 0.00127 0.001273 0.001 4.1 248.1140 1.132 176.19 1.25 0.08 1.211 161.54 1.09 0.001251 0.001253 0.001 4.4 265.2144 1.137 177.03 1.24 0.079 1.216 161.6 1.1 0.001232 0.001234 0.001 4.8 283.6148 1.142 177.86 1.24 0.078 1.22 161.65 1.1 0.001213 0.001215 0.001 5.2 303.6152 1.147 178.7 1.23 0.077 1.225 161.7 1.11 0.001195 0.001197 0.001 5.7 325.6156 1.153 179.54 1.23 0.077 1.229 161.75 1.11 0.001177 0.001179 0.001 6.3 349.7160 1.158 180.38 1.22 0.076 1.234 161.81 1.11 0.001159 0.001161 0.001 7 376.5164 1.163 181.22 1.21 0.075 1.238 161.86 1.12 0.001142 0.001144 0.001 7.8 406.4168 1.168 182.06 1.21 0.074 1.243 161.91 1.12 0.001125 0.001127 0.001 8.9 440.3172 1.173 182.9 1.2 0.074 1.247 161.97 1.13 0.001108 0.00111 0.001 10.3 479.1176 1.179 183.74 1.2 0.073 1.252 162.02 1.13 0.001092 0.001094 0.001 12.1 524.5180 1.184 184.58 1.19 0.072 1.256 162.07 1.14 0.001076 0.001078 0.001 14.6 578.8184 1.189 185.42 1.19 0.072 1.261 162.13 1.14 0.00106 0.001062 0.001 18.3 646.1188 1.194 186.27 1.18 0.071 1.265 162.18 1.15 0.001045 0.001047 0.001 24.5 733.8192 1.199 187.11 1.18 0.071 1.27 162.23 1.15 0.001029 0.001031 0.001 36.4 858.7196 1.205 187.95 1.17 0.07 1.275 162.28 1.16 0.001015 0.001016 0.001 69.6 1074.4200 1.21 188.79 1.17 0.069 1.279 162.34 1.16 0.001 0.001002 0.001 632.6 2133.1204 1.215 189.63 1.16 0.069 1.284 162.39 1.17 0.000986 0.000988 0.001 -91.5 2500
k
ECHO OF INPUT:
Discharge Q = 220.075 m3 s-1 Bottom width B = 60 m Side slope z = 5 m/m
Bottom slope So = .001m/m Manning's n = .03
Specified flow depth at the downstream boundary yd = 0.95 m
Number of computational intervals n = 200 Number of tabular output intervals m = 50
OUTPUT:
Computational depth interval Δy = 0.0013 m Tabular output depth interval (Δy)t = 0.005 m
Normal depth yn = 1.21 m Normal-depth Froude number Fn = 0.345
Hydrology Report Bridge 4/1 Weligama–TelijjawilaB466 Road Scour Calculation.
Provision in Essentials of Bridge Engineering (D . Johnson Victor) Mean Depth of Scoure Dsm = 1.34 (Db2/Ksf) 0.33 Db = Discharge in m3/s per m Ksf= Silt Factor (Lacey Method) 1.2445 for 0.5mm Medium sand. For Denipitiya Bridge Total Discharge 220.075 m3/s Width = 95m Therefore Db = 2.33 Dsm= 2.18 m Calculation of Scour For nose of piers Maximum Scour depth From HWL = 2.0* Dsm = 4.36 m Maximum Scour depth from river bed = Dmax – HWL Calculated HWL=4.30m Therefore minimum Depth required for foundation = 0.06m
3 Conclusions and Recommendations
3.1 Conclusions 1. Calculated HFL is 1.205 as per the Backwater effect .
2. The Soffit level of the proposed bridge is 2.267mMSL.
3. Since the effect of backwater is critical in this sea area the free board is 1.062m.
4. While considering the sea water levels it is revealed that the Proposed Bridge will not be submerged by rare
floods of high magnitude.
3.2 Recommendations
1. The proposed soffit level 2.267.mMSL is recommended.
