A CASE STUDY OF GULLY EROSION IN THE ETHIOPIAN HIGHLANDS:

THE WARKE WATERSHED

A Project Paper

Presented to the Faculty of Graduate School

of Cornell University

in Partial Fulfillment of the Requirement for the Degree

Master of Professional Studies (MPS)

by

Birara Chekol Tarekegn

January 2012

© 2012 Birara Chekol Tarekegn

ABSTRACT

Gully erosion affects large areas in Ethiopia. It is the source of sediment in the rivers

and takes agricultural land of production. Understanding factors for gully expansion is

essential for application of effective preventive and remedial measures towards

sustainable land resources management. Therefore, the objective of this study is to

study the underlying causes of the rapid gully expansion, to recommend strategies to

prevent further gully formation and to reclaim existing gullies.

The research was conducted in Warke watershed at an altitude between 2632- 2500 m

in the upper Blue Nile Basin, Ethiopia. The area has a humid monsoon climate with an

average annual rainfall of 1300 mm. Thirty years ago, gully formation started after the

area became intensively cultivated. Gullies have expanded continuously since that

time. Structural and biological conservation measures to try to stop the gully

expansion have been installed in the whole watershed and maintained in one part of

the watershed.

Piezometers were installed at the top hill, middle, and bottom outlet of both

watersheds. Average gully width, depth and lengths were measured using measuring

tape at the beginning and end of the rainy season. Soil Infiltration rates were also

measured using single ring infiltrometer. Long and short term erosion rates were

estimated using AGERTIM (Assessment of Gully Erosion Rates through Interviews

and Measurements).

Fifty years old land users in a group discussion recalled that gully formation started in

the1980’s when farm plots were demarcate/separate using traditional small waterways

(locally called Fesses) along the slope. Erosion rates since the initiation of the gullies

were 22 t/ha/yr and 58 t/ha/yr for the two gullies in the watershed with the

conservation practices and 48 t/ha/yr for the gully in the area without conservation

practices. Short term soil loss rates were many times greater indicating that these

gullies were in their acceleration phase. Since rainfall exceeds the evaporative demand

of the crop a perched water table formed over the restrictive layer during the rainy

monsoon phase. The water table was generally deeper in the upper watershed than at

lower elevations where the slope decreased. Active gully formation occurred in areas

where the groundwater was above the gully bottom. Since infiltration was in general

greater than the prevailing rainfall intensities and most of the rainfall infiltrated in the

soil, gully function was caused by subsurface flow and not by surface flow.

Key words: Gully erosion, subsurface flow, saturation excess, infiltration excess,

gully expansion, piezometer, treated area, untreated area, and soil loss

rate.

iii

BIOGRAPHICAL SKETCH

Birara Chekol Tarekegn was born from his father Chekol Tarekegn and his mother

Enatnesh Netsere in Dangla District of Awi Administrative Zone of Amhara National

Regional State, Ethiopia. He graduated with BSc degree of Land Resource

Management and Environmental Protection major in Soil and Water Conservation

from Mekelle University in July 16, 2006 and diploma of Agricultural Engineering

and Technology in 1990 at Awassa College of Agriculture in Addis Ababa University.

He worked for Bureau of Agriculture and Rural development with different positions.

Then he attended Master’s Program in integrated watershed management and water

supply from 2010 to 2011. He also has a great interest to pursue his PhD on sediment

modeling, soil physics, climatic changes or water resources management.

iv

ACKNOWLEDGMENTS

My profound sincere thanks go to professor Tammo Steenhuis for his enthusiastic and

unlimited support from shaping the idea up to materializing the work. I am grateful for

his frequent supervision both in the field and in class as well as other social matters.

He also provided me relevant literatures in due work. I extend my special sincere

thanks and appreciations to Dr. Amy S. Collick, the coordinator of the master

program, for her untiring effort in fulfilling the essential academic and logistic

services in the university. My special thanks also go to Seifu Admassu for the friendly

assistance and continuous interest to help me on the study and providing me important

literatures.

Special thanks to First Presbyterian Church, Ithaca, New York for the financial help I

got from International Hunger Student Field Support program. The support allowed

solving financial problems which my family was facing. I utilized the money for my

family during the time that the monthly salary which I was getting from BoA was quitted

for three months. My family would have been in problem without the support.

I am pleased for the help I received from Essayas Kaba (lecturer, School of Civil and

Water Resources Engineering) and Addisalem who helped me in GIS works, Wubneh

Belete allowed me to use Soil Auger for drilling piezometer holes, Birkneh Abebe,

Getachew Engidayehu and Nigist Birhanu allowed me to use their computers, other

office equipments and surveying materials for my work. It was not possible to

accomplish the manuscript with out there help.

My admiration goes to my wife, Adanech Wolel and my children Hiwot and Mehari

who, their love and encouragement. My wife was courageous enough to handle

household matters.

v

Last but not least, I would like to acknowledge the scholarship from the Cornell

University and financial support from HED for the whole study program.

vi

TABLE OF CONTENTS

BIOGRAPHICAL SKETCH ......................................................................................... iii 

ACKNOWLEDGMENTS ............................................................................................. iv 

TABLE OF CONTENTS .............................................................................................. vi 

LIST OF FIGURES ....................................................................................................... ix 

LIST OF TABLES ........................................................................................................ xi 

LIST OF ABREVIATIONS ......................................................................................... xii 

CHAPTER ONE ............................................................................................................. 1 

1  GENERAL BACKGROUND ..................................................................... 1 

1.1  Introduction ................................................................................................. 1 

CHAPTER TWO ............................................................................................................ 4 

2  MATERIALS AND METHODS ................................................................ 4 

2.1  Description of the Warke watershed ........................................................... 4 

2.2  Methodology ............................................................................................... 4 

2.2.1  Meteorological data ........................................................................... 5 

2.2.2  Soil infiltration test ............................................................................ 6 

2.2.3  Sub-surface water table measurement ............................................... 6 

2.2.4  Gully volume determination .............................................................. 7 

2.2.5  Runoff data ......................................................................................... 9 

2.2.6  Soil physical properties ...................................................................... 9 

CHAPTER THREE ...................................................................................................... 11 

3  RESULT AND DISCUSSION ................................................................. 11 

3.1  Long term evolution of gully in Warke watershed ................................... 11 

3.2  Soil infiltration rate, bulk density and texture ........................................... 15 

3.3  Ground water table trigger gully expansion .............................................. 17 

vii

3.4  Runoff ....................................................................................................... 24 

3.4.1  Short term evolution of gully volume and soil erosion rate in the

study watershed ................................................................................ 25 

CHAPTER FOUR ........................................................................................................ 29 

4  Conclusions and Recommendations ......................................................... 29 

4.1  Conclusions ............................................................................................... 29 

4.2  Recommendations ..................................................................................... 30 

5  REFERENCES .......................................................................................... 32 

APPENDICES .............................................................................................................. 36 

Appendix 1: Example of a measured gully cross-section .................................. 36 

Appendix 2: Short term evolution of the three considered gullies measured at

the beginning and end of rainy season .............................................................. 38 

Appendix 3: Surface Runoff Discharge in the Untreated Area (measured under

weir_1) ............................................................................................................... 39 

Appendix 4: Surface Runoff Discharge in the Treated Area (measured under

weir_2) ............................................................................................................... 40 

Appendix 5: Measurements and observations undertaken at different parts of

the watershed for the identification and determination: gully incision and

expansion factors. .............................................................................................. 41 

Apendix 6: Figures at the top part of the watershed; left side before 9years,

right side after reclamation. Birara was working there in the district. The result

seems good at the top part of the watershed while, gullies are expanding at

middle of the watershed due to subsurface flow and ground water push effect in

the bottom saturation area. ............................................................................... 42 

Appendix 7: Figures at the bottom outlet of the watershed showing gully slides

due to subsurface water rise up to the surface and soils saturation. ................ 43 

viii

Appendix 8: Observed Gully incision due to subsurface water flow in the

middle treated area of gully_1 and outlet bottom saturated area of the

watershed. .......................................................................................................... 44 

Appendix 9: Daily recorded water table depth (m) in Warke watershed from

July to October 2010. ........................................................................................ 45 

Appendix10: Questionnaire for the study Gully formation and expansion

Characteristics in the high lands of Blue Nile basin, Ethiopia. ........................ 48 

ix

LIST OF FIGURES

Figure 1: Photos describing Gully I at different locations in time and space. A) Gully

in the upper part of the watershed in 2000. B) Same gully as in a depicted in 2010

when it fully reclaimed. C) Recent gully formed in the middle part of the watershed.

D) Recent gully formed in the bottom part of the watershed. ........................................ 3 

Figure 2: Location of the research area; gully I located west watershed boarder (flame

red) and parallel to the road, gully II (topaz sand), gully III (quetzal green) and gully

IV (medium apple) east of the watershed consecutively to the right. ............................ 5 

Figure 3: Gully I parallel to the road and getting (sub) surface flow from the treated

part of the watershed. Slumping from its right side and increasing in width. ................ 8 

Figure 4: Short term evaluation of saturation bottom gully (gully at the junction of

gullies I and III gully eating up in the bottom of the watershed where saturation is high

and ground water table was near the surface. ............................................................... 10 

Figure 5: The dimensions of a rectangular weir constructed at the outlet of gully III

(representing untreated part of the watershed) ............................................................. 10 

Figure 6: local saturation in the farmlands causing to collapse the side wall of gully II

in the middle of the watershed ...................................................................................... 12 

Figure 7: New head cuts occurring in the saturated bottom and treated middle part of

the watershed eating up and side due to soil saturation. ............................................... 14 

Figure 8: Average soil infiltration rate in the treated Vs untreated area of the

watershed within the three topographic positions (top, middle and bottom) of the

watershed ...................................................................................................................... 17 

Figure 9: Average groundwater table height and location of 28 piezometers. Locations

of gully slips are indicated by small triangles .............................................................. 19 

x

Figure 10: Water table above the restrictive layer both in the treated and untreated top

(A), middle (B) and bottom (C) part of the watershed. ................................................ 20 

Figure 11: The relative depth of water table vs. gully depths in the selected gullies

(gully I, gully II and gully III) at the points where short term Gully evolution

measurement were taken place during the end of the rainy season. ............................. 21 

Figure 12: Piping erosion occurring at the bottom part of the watershed during the

month September first. ................................................................................................. 22 

Figure 13: Piping erosion occurring at the bottom part of the watershed. ................... 23 

Figure 14: Average monthly rainfall in 2010 in Warke watershed, where high rainfall

was registered in the month June .................................................................................. 25 

Figure 15: Time series Runoff discharge in the treated and untreated area; the figure

shows only the runoff measured during the period mid July to September end where

the measurement was undertaken. ................................................................................ 26 

Figure 16: Short term percentage volume evolution of the three selected gullies. ...... 27 

Figure 17: Farm land where the three to four times tillage operations have been

undertaken and prone to runoff erosion at the beginning of the rainy season. Actually

what you can see is the interflow in plowed land that surfaces at the border where it

becomes over ................................................................................................................ 28 

xi

LIST OF TABLES

Table 1: Event calendar used in interview ..................................................................... 5 

Table 2: Depth and location of piezometers below the surface ground ......................... 7 

Table 3: Age of the studied gully segments in Warke watershed, as estimated by local

informants ..................................................................................................................... 11 

Table 4: The dimension of selected gullies measured beginning and end of one rainy

season. .......................................................................................................................... 14 

Table 5: Long and short term rates of gully erosion in GI, G II and G III Warke

watershed ...................................................................................................................... 15 

Table 6: Average soil infiltration rate at different topographic locations within the

treated and untreated parts of the watershed. ............................................................... 16 

Table 7: Summary of the measured parameter average values and change in

percentage of gullies; Gully, Gully, Gully and saturation bottom gully ...................... 24 

xii

LIST OF ABREVIATIONS

ATW: Average top width

AWM: Average middle width

ABW: Average bottom width

AD: Average depth

ANRS: Amhara National Regional State

BoA: Bureau of Agriculture

SLMP: Sustainable Land Management Programme

SWCP: soil and water conservation practices

PDRE: People’s Democratic Republic of Ethiopia

PIZ: Piezometer

WT: Water table

Ha: hectare

T: Tone

Yr: year

PVC: polyvinyl chloride

M: meter

xiii

GI: gully I

GII: gully II

GIII: gully III

GaSB: gully at saturation bottom

1

CHAPTER ONE

1 GENERAL BACKGROUND

1.1 Introduction

The Ethiopian highlands contribute most of the water that is used in Sudan and Egypt.

The Blue Nile provides more than 60% of the Nile flow in Egypt (Ibrahim, 1984;

Conway and Hulme, 1993) and carries about 140 million tones of soil per year

(Garzanti et al., 2006). This is equivalent to 7 t/ha/yr soil or on the average 0.5 mm

depth per year over the entire Blue Nile basin. This sediment before the construction

of the dams was the source of the soil fertility in Egypt, but currently is a nuisance

(Bekele, 2003). It fills up the man-made reservoirs and in most places it slowly bleeds

the Ethiopian agricultural lands from its fertility. In other sensitive places it erodes

away the agricultural land completely. Fertility loss with shifting cultivation was

replaced during the fallow period but with the continuous cultivation under the

increased population pressure (Hurni, 1988; Bewket and Sterk, 2003), it can be only

maintained with artificial fertilizers that in many cases are too expensive.

Splash, sheet and rill erosion and gully formation are the different forms of soil loss.

Gullies are defined as “a channel resulting from erosion and caused by the

concentrated but intermittent flow of water usually during and immediately following

heavy rains; Deep enough to interfere with, and not to be obliterated by, normal tillage

operations” (American Soil Science Society, 1984). Gullies are one of the most

destructive forms of erosion, damaging farmland and difficult to reverse (Billi and

Dramis, 2001; Moges and Holden, 2009). Gullies can be formed either by surface

runoff (Casali et al., 1999: Valentin et al., 2005) or by saturation of the soil profile

(Vandekerckove et al., 2000, Valentin et al., 2005 and Tebebu et al., 2010). Land use

2

change in the watershed commonly triggers gully formation (Natchtergale et al., 2002,

Vanwalleghem et al., 2005a, Thomas et al., 2004 all cited in Valentin et al., 2005).

Gullies and are affected by a wide array of factors and processes.

Splash, sheet and rill erosion have been studied in the laboratory and at the plot scale

and are therefore relatively well understood (Wells et al., 2009). Gully erosion

processes are three dimensional in nature generally (Valentin et al., 2005) less well

known because it occurs at the landscape scale (Poison et al., 2003). Moreover, there

are few gully erosion studies in Ethiopia especially on the Nitosol dominated

northwestern Ethiopian highlands and consequently processes in gully formation are

not well understood. Therefore, the general objective of the research was to better

understand gully formation and to identify factors that determine gully formation and

expansion. The specific objectives of the study are:

To determine the impact of hydrological process in gully formation and

expansion in the area.

To identify the effect on gully formation of previously installed soil and water

Conservation practices to stop gully formation.

To recommend measures to halt gully formation and expansion in the area.

The research was carried out in the Warke watershed located 140 km south of Bahir

dar, Ethiopia. Gully formations started thirty years ago after the area became

intensively cultivated (Figure 1). At the end of the nineteen nineties, graded soil bunds

and Fanyajuu (“Throw uphill” in Swahili) were installed throughout the watershed to

try to stop gully formation. In addition, check dams were constructed and planted with

tree Lucerne (Chamaecyticuspalmensis), vetiver grass, Acacia abyssinica, acacia

3

decurrens, or Acacia nilotica. In the upper watershed, both the graded bunds brought a

reduction in soil loss and the check dams and gully site plantation resulted in

reclamation of the gullies (Figure 1a, 1b). However, gullies expanded unexpectedly in

the middle and lower areas. These gullies that started in the middle area continued to

expand upslope and down slope and increased both in depth, width and branched

sideways (Figure 1c, 1d).

In one part of the watershed a guard was hired and the conservation practices

remained in place up to this date (the “treated watershed”) while in another part the

conservation practices were destroyed (the “untreated watershed”). These two sub

watersheds provide a way to evaluate the effectiveness of the soil and water

conservation practices on gully formation as well as give an insight in processes that

are involved in gully formation.

Figure 1: Photos describing Gully I at different locations in time and space. A) Gully in the upper part of the watershed in 2000. B) Same gully as in a depicted in 2010 when it fully reclaimed. C) Recent gully formed in the middle part of the watershed. D) Recent gully formed in the bottom part of the watershed.

4

CHAPTER TWO

2 MATERIALS AND METHODS

2.1 Description of the Warke watershed

The Warke Watershed which is located in the Ethiopian highlands of Blue Nile Basin

140 km south from Amhara National Regional State (ANRS) capital Bahir dar (Figure

2). Its area is about 95ha. It is part of one of the 35 Sustainable Land Management

Program (SLMP) watersheds called Yesir; in which the government of Ethiopia has

demonstrated its commitment to restore, and enhance the agricultural productivity

(FDRE, 2008). The climate is sub humid monsoon climate with a monomodal rainfall

distribution and annual rainfall of 1300 mm/year. It ranges in elevation from over

2,500 m to 2,630 m. The soils in the basin are classified as Nitosols which are deep

with a clay-rich sub soil, and good soil structure (FAO Soter database 1997). The area

is characterized by intensive agriculture with an average land holding of 0.65 hectares

per household. Land preparation is performed with the traditional Maresha plow

pulled by a pair of oxen. Barley, wheat, beans and peas are the major crops usually

sown at the same time to minimize bird damage. Sheep and cattle are allowed to graze

the cropland after harvest.

2.2 Methodology

Although several methods exist to determine gully expansion such as high resolution

satellite images (Moges and Holden 2009, Daba et al., 2003) and the

dendrochronological method (Ireneusz, 2006), the AGERTIM (Assessment of Gully

Erosion Rates through Interviews and Measurements) developed by Nyssen, et al.,

(2006) was chosen allowing us to understand the historic context of the gully

5

development (Nyssen et al., 2006). As part of this method the watershed area was

visited with interviewees as a group and on an individual basis. The field visit allowed

the interviewees to recall the changes in the area when they were young.

Discussions were held with a prepared frame work in a semi-structured way (“when is

Gully incision started?”, “In which part of the watershed was incision started first?”,

“How was it started?”, “how deep was the gully?”, “How do you evaluate its

increment in depth, length and width?”). For supporting the farmers in recalling the

relative and absolute time, an event national calendar was prepared (Table 1). The

following steps were used in obtaining historical information about the area: (i) one

walk with 19 selected informants in the major gully area, (ii) semi-structured

individual interviews and (iii) semi-structured key informants group interviews. Group

discussions included the two guards that have been guarding the conservation

structures since the 1994 in the treated watershed.

Table 1: Event calendar used in interview

Year Event

1996 Land reform in the area

1989 Down fall of farmers cooperatives association due to the policy amendment by the Derg regime from socialism in to mixed economy

1983 Organization of farmers’ cooperatives

2.2.1 Meteorological data

The daily rainfall data for 2010 was measured at the Burie station 6 km from the

watershed. In annual 2010 precipitation was 1424 mm which is greater than the annual

average of 1300 mm.

5

Figure 2: Location of the research area; gully I located west watershed boarder (flame red) and parallel to the road, gully II (topaz sand), gully III (quetzal green) and gully IV (medium apple) east of the watershed consecutively to the right.

5

6

2.2.2 Soil infiltration test

Infiltration rates were measured with a single ring infiltrometer driven15cm into the

soil. Fifty cm of water was poured into the ring both in the treated and untreated

watersheds. The drawdown of water in the ring was recorded using graduated ruler.

Three infiltration measurements were made at the top, mid-slope and bottom part of

the watershed.

2.2.3 Sub-surface water table measurement

Twenty-eight piezometers (Table 2) were installed in the watersheds in transects along

and perpendicular to the gullies and head cuts (Figure 1) to determine the effect of the

subsurface water on gully expansion. Piezometers consisted of 5 cm diameter PVC

pipes with 1 cm diameter holes drilled at the bottom 30 cm of the pipe and covered

with cultural cloth called Abujedi made locally to prevent intrusion of silt and sand.

The bottom end of the piezometer was capped with a fixed plastic cap, while the top

end of the piezometer had a removable plastic cap.

Holes were drilled for piezometer installation with a hand auger to either the depth of

the impermeable layer or water table. The deepest piezometer was 3.8 m in the middle

of the watershed. In the bottom part drilling was halted when the water table at around

2.5 m was reached. The impermeable layer was estimated at 4 m (Table 2). The water

level in the piezometer was recorded daily by the two technicians in less than an hour.

Ground water table heights other than measuring points were determined by

interpolation.

7

2.2.4 Gully volume determination

Although there are four gullies in the research area, the three largest gullies were

selected. The large gully which is located partly at the western border of the watershed

was named Gully I, the middle gully located inside the treated watershed was named

Gully II and Gully III was located in the untreated watershed (Figure 2). Gully I at the

lower boundary of the treated area collects both surface and as subsurface flow from

the treated watershed. The gully expands only on the upslope side (Figure 3) where

surface and subsurface runoff is coming into the gully.

Table 2: Depth and location of piezometers below the surface ground

Code Elevation

(masl)

Depth of Piezometer

(m)

Average depth of water table from the surface (m)

Elevation of Average Water Table (masl)

Location in the Watershed

P_1 2513 2.70 0.87 2512.13 Saturation bottom P_2 2516 2.90 2.41 2513.59 ″

P_19 2536 3.55 2.60 2533.40 Treated bottom P_20 2540 3.69 2.40 2537.60 ″ P_16 2556 2.54 1.78 2554.22 Treated middle P_18 2544 3.65 2.67 2541.33 ″ P_15 2569 3.70 3.12 2565.88 Treated top P_17 2553 2.65 2.08 2550.92 Treated middle P_21 2544 3.55 2.28 2541.72 ″ P_22 2549 3.60 2.88 2546.12 ″ P_23 2553 3.65 2.00 2551.00 Treated middle P_24 2557 2.48 1.69 2555.31 ″ P_25 2557 3.10 2.31 2554.69 ″ P_26 2564 2.10 1.38 2562.62 ″ P_27 2580 2.33 1.59 2578.41 Treated top P_28 2573 2.20 1.38 2571.62 ″ P_3 2522 1.88 1.50 2520.50 Untreated bottom P_4 2537 1.90 1.79 2535.21 ″ P_5 2568 2.90 2.72 2565.28 Untreated middle P_6 2576 3.00 2.91 2573.09 ″ P_7 2589 3.60 3.57 2585.43 ″ P_8 2602 1.90 1.89 2600.11 Untreated top P_9 2614 3.40 3.40 2610.60 ″

P_10 2621 3.55 3.55 2617.45 ″ P_11 2614 3.60 3.60 2610.40 ″ P_12 2591 1.89 1.88 2589.12 Untreated middle P_13 2583 3.25 3.19 2579.81 ″ P_14 2579 3.80 3.77 2575.23 ″

8

The volume of the three gullies were measured in July at the beginning of the rainy

phase of the monsoon (called 2009 measurement) and end of the rainy phase in

December, (called the 2010 measurement). The dimensions of the saturated area near

the watershed outlet were taken more frequently (Figure 4). Both long term and short-

term soil loss from gullies were estimated from the volume measured. Gully volume

was determined from the cross sectional area of the gully and the length between gully

segments. The cross sectional area was determined by measuring the cross section of

the gullies (Appendix 1). The coordinates of the gully were determined with a hand

held Garmin Etrex global positions system (GPS) receiver (Garmin International, Inc.,

Olathe, Kansas) with 2m accuracy. The distance between cross-sections was measured

using a 50m long surveyor’s tape. The total volume was calculated using the cross

sectional areas and the total length.

Figure 3: Gully I parallel to the road and getting (sub) surface flow from the treated part of the watershed. Slumping from its right side and increasing in width.

9

2.2.5 Runoff data

Rectangular concrete weirs (Figure 5) were installed in the outlets of the treated

watersheds (Weir 2, W2) below the junction of Gullies I and II) and untreated

watershed in Gully III (Weir 1, W1) to measure surface runoff. The slope of the

ground surface at W1 is 3% and W2 is 5%. Since runoff measurement was done

manually, runoff during the night time was missed and therefore only day time storms

are compared. The stage discharge curve was determined with the float method. The

velocity of water near the weir was measured with small floating circular ball and the

depth of flow with a ruler.

2.2.6 Soil physical properties

Fifteen soil samples were collected from piezometer sites and in the gully banks to

define the physical characteristics of soils in the watershed. Soil bulk density was

determined at Amhara National Regional soil laboratory with standard core sampler

and oven drying at 105oC for 24 hours and soil texture determination by hydrometric

and wet sieve grain size determination methods.

10

Figure 4: Short term evaluation of saturation bottom gully (gully at the junction of gullies I and III gully eating up in the bottom of the watershed where saturation is high and ground water table was near the surface.

Figure 5: The dimensions of a rectangular weir constructed at the outlet of gully III (representing untreated part of the watershed)

11

CHAPTER THREE

3 RESULT AND DISCUSSION

3.1 Long term evolution of gully in Warke watershed

According to the interviews, before 1980 visible gullies did not exist. They indicated

that gully formation started at the time when many more farmers came into Warke

Watershed that were evicted from their land by the Derg regime for establishing

farmers’ cooperatives for members only in 1983 (Table 1). As the result of the

evictions, redistribution of farm land took place in the Warke watershed. The land that

was owned by a small number of farmers was shared among a much larger group

resulting in division of the farm lands in smaller pieces. Small ditches were

constructed at farm boundaries to carry of excess water. Based on this information

Gully I started in 1980 and Gullies II and III around 1987 (Table 3). A small gully

formed just in the outlet of gully III called GaSB in 2007 (Table 3).

Table 3: Age of the studied gully segments in Warke watershed, as estimated by local informants

Description Incision started G I 1980 G II 1987 G III 1987 GaSB 2007

To control the expansion of the gullies the district office of agriculture in cooperation

with the community started to install soil and water conservation structures in the year

1999 consisting of graded soil bunds on the farm land, grass, forage trees and other

nitrogen fixing plant along the gullies and on the graded soil bunds, stone and brush

check dams inside the gullies. In part of the watershed guards were hired to protect the

SWCP (gullies I and II) while the watershed with gully III was not guarded. As a

12

result the graded bunds and planting were destroyed during the years from 2000 to

2003. Gullies as a result of check dams filled up and were eventually converted to

agricultural land.

Gullies in the middle and bottom part increased in size and retreated back in the area

that was reclaimed even in the treated part of the watershed continued to increase and

another new head cuts emerged on the side of the formers. Traditional drainage

ditches at a slightly greater slope were constructed upslope of the graded bunds.

According to interview with farmers the bunds were effective in reducing runoff speed

but increase the water logging. The traditional graded ditches drained the excess water

from the field. According to the farmers some of the water flowed over the plow pan

to the gully where it cause local saturation just below the surface and slumping of the

soil below it making the v shaped banks (Figure 6). In order to understand better how

the gullies were formed we will look next at the physical measurements taken in

Warke watershed in 2010.

Figure 6: local saturation in the farmlands causing to collapse the side wall of gully II in the middle of the watershed

13

In 2010 the length of the three (G I, G II and G III) was 890 m, 755 m and 1010 m and

did not increase because the gullies had reached the upper end of the watershed. The

gullies were still widening and deepening (Table 4). Most change occurred in the

bottom gully after gullies G I, G II and G III are joined. The volume increase was over

500% in the two months of observation (Table 4, Figure 7 and Appendix 7).

The area taken up in 2010 by the three gullies 0.79 ha (Gully I), 0.44 ha (Gully II),

0.52 ha (Gully III) and 0.25 ha (gully below the junction of Gullies I, II and III)

accounts for about 2.5% of the total watershed area. The long term gully erosion rates

varied between 22 and 58 t/ha/yr for Gullies I and II in which the SWCPs were

maintained and 48 t/ha/yr for Gully III without SWCP (Table 5). The smaller erosion

long term rate for Gully I is caused by the fact that it is in existence for 30 years

compared to 23 years for the other two gullies and has the largest drainage area (Table

5). By itself Gully I is larger than any of the other two gullies (Table 4) but only

expands on the uphill side.

Similarly to other gullies that start slow then grow exponential and become stable once

it reaches the upper part over a 40 year period (Tebetu et al, 2011), the gullies in the

Warke watershed are in their exponential growth rate stage with erosion rates as high

as 292 t/ha/year for gully II (Table 5). The lower short term erosion rate for Gully I

per unit watershed area is caused again by the larger watershed, but also it is likely

closer to becoming stable because it is 30 years old (Tables 4 and 5). The short term

erosion rates of gullies II and III is similar to those observed in the DebreMawi

watershed 30 km south of Bahir Dar (Tebetu et al. 2010) where gully formation started

also around the same time. Erosion rates of Gully I is equal to the ones where gully

formation started earlier such as Herwegand Ludi (1999) and Nyssen et al. (2006).

14

Table 4: The dimension of selected gullies measured beginning and end of one rainy season.

Description G I G II G III GaSB Total E

valu

atio

n P

erio

d

Beg

inn

ing

of

rain

y se

ason

(2

010)

Length (m) 890.0 754.9 1,010.0 2.6 Av. Depth (m) 3.1 2.2 2.0 1.8

Av. width (m) 4.9 3.4 3.4 1.8 Volume (m3) 13,683.8 5,697.6 6,904.6 8.4 26,294.3 plan area (m2) 7,253.5 3,940.5 4,969.2 4.6

En

d o

f ra

iny

seas

on (

2010

) Length (m) 890.0 754.9 1,010.0 6.4 Av. Depth (m) 3.3 2.5 2.2 2.7 Av. Width (m) 5.4 4.0 3.6 3.0 Volume (m3) 15,685.5 7,310.7 8,189.2 51.3 31,236.6 plan area (m2) 7,867.6 4,453.9 5,211.6 21.2

Volume change in% 14.6 28.3 18.6 511.8

Figure 7: New head cuts occurring in the saturated bottom and treated middle part of the watershed eating up and side due to soil saturation.

15

Table 5: Long and short term rates of gully erosion in GI, G II and G III Warke watershed

Variable Vo

(m3) V (m3)

Bulk density (g/cm3)

Gully segment

age estimated by local

informants (yr)

Catchment area (ha)

Rs (t/ha/yr)

RL (t/ha/yr)

G I 13684 15,685 1.23 30 29.6 83 22

G II 5698 7,311 1.24 23 6.8 292 58 G III 6905 8,189 1.25 23 9.4 172 48 GaSB 8. 51 1.22 2 3.5 15 9 Total 26,294 31,236Area

weighted average

1.24 19.50 49.29 68.2 16.80

3.2 Soil infiltration rate, bulk density and texture

The soil texture analysis indicated that the Warke watershed had a sandy loam (59%

sand, 24% silt and 17% clay). The mean bulk density based on 15 samples taken from

the treated and untreated part of the watershed was 1.24 g/cm3. Infiltration rates were

measured both in the treated and untreated part of the watershed. The infiltration rates

were greater in the treated watershed especially at the top than the untreated watershed

(Table 6 and Figure 8) the smaller infiltration rate at the bottom of the hill (Table 6)

could be due to the saturation of the soil profile. When the soil is saturated or near

saturation there is very little space left for the water to infiltrate and will pond. The

average soil infiltration rate for the treated watershed was about 6.1 m/day while for

the untreated area was 4.0 m/day. The infiltration rates that are expected for sandy

loam soils are generally greater than the observed rainfall intensities assuming that the

rainfall intensities are comparable the Maybar and AnditTid watershed in eastern

Amhara receiving approximately the same annual rainfall (Bayabil et al, 2010).

Rainfall burst during a rainstorm will be larger than the infiltration capacity and

16

surface runoff can occur but will then infiltrate after the rainfall intensity decreases.

Despite the high infiltration rates, farmers reported runoff at times especially after

plowing. In addition, the drainage ditches installed by farmers at some locations

indicates that infiltration is problematic at times. Farmers reported increased moisture

content near graded bunds (and installed therefore drainage ditches) indicating lateral

flow (either surface or subsurface). Farmers’ interviews also indicated that the gully

erosion was caused by interflow over the denser than sub layer. It is likely that soil

crusting or more likely a shallow clay enriched zone under the plow pan might hinder

infiltration during the rain storm and cause shallow lateral flow.

Table 6: Average soil infiltration rate at different topographic locations within the treated and untreated parts of the watershed.

Location in the watershed

Infiltration rate ( mm/hr) Land use Slope

Treated part Untreated part Top 144 136 cultivated 19 Top 549 216 cultivated 19 Top 430 160 cultivated 19

Middle 198 153 cultivated 9 Middle 281 185 cultivated 9 Middle 293 472 cultivated 9 Bottom 23 23 cultivated 3 Bottom 115 115 cultivated 3

17

Figure 8: Average soil infiltration rate in the treated Vs untreated area of the watershed within the three topographic positions (top, middle and bottom) of the watershed

3.3 Ground water table trigger gully expansion

The depths of groundwater in the watershed varied with position in the landscape.

Down slope in the lower part of the watershed the water table was within one meter

from the surface. In the upper watershed ground water table was below 3 m (Figure 9).

Thus going upslope the water table decreased. The deeper depths in areas in the upper

and right hand site of Figure 9 did not have piezometers and therefore the water table

depths are uncertain. Furthermore, since the area from south end of the watershed is

not close to a piezometer, the interpolation was not valid. Hence, as we move from

P_1 to the south border of the watershed, the deep blue color (Figure 9) does not

represent the real water table depth.

The pattern of the water table depth with time is dependent on rainfall amounts and

landscape position (Figure 10). The response between piezometers is highly variable

but some general trends can be observed. First, as indicated by the different scales on

0

100

200

300

400

500

600Ave

rage  soil Infiltration rate(m

m/hr)

Topographical location

Infiltration rate at in the treated Vs untreated area at different location

 Infiltration ratetreated part ( mm/hr)

 Infiltration rateuntreated part( mm/hr)

18

Figure 10 a, b and c, the water table height above the restrictive layer for piezometers

located in the top, middle and lower part, respectively, is increasing with down slope

position. Second, the water level is greater in the beginning of August then in October,

because the month of July had much more rainfall than August and September (Figure

14). Thus, the profile is drying out and all water tables are going down. The rates of

drawdown are different and not smooth. Thirdly, the decline is not smooth and does

not occur per every perimeter. When the water level is either at the restrictive layer or

at the soil surface, the water level is steady. Super imposed on the general trend is

water level increases due to rainfall events. Generally, the recession is much faster for

the individual events than for the overall trend. Finally there is not a systematic

difference between the treated and untreated.

For gully formation it is of interest to find where the water table is above the gully

bottom. Gully I (Figure 11a) is parallel to the road for a part which is down slope of

the gully. The gully slumps only upslope of the road and not at the down slope side

Upslope there is a high water table all along the gully (Figure 11a). In the other gullies

water table is only a few places (Figure 11b, c). For Gully I the road stops the

interflow from upslope because of compaction of the subsoil, and as a result the water

table rises and once the gully is initiated it will proceed rapidly upstream and becomes

wider, where the road is down slope of gully I (Figure 3). The same phenomena of a

gully at a distance 10-20 m from the road and parallel can be seen in many places in

Amhara. Thus it is not the surface runoff of the road directly that causes the gully but

the additional water of the road causes saturation of the soil that in turn decreases the

cohesiveness of the soil and once a gully initiates it will proceed rapidly up and down

hill.

19

Figure 9: Average groundwater table height and location of 28 piezometers. Locations of gully slips are indicated by small triangles

20

Figure 10: Water table above the restrictive layer both in the treated and untreated top (A), middle (B) and bottom (C) part of the watershed.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

P_10untreated top

P_11untreated top

P_15 treatedtop

P_28 treatedtop

wat

er le

vel a

bov

eth

e re

stri

ctiv

e la

yer(

m)

A

0.00

0.50

1.00

1.50

2.00

P_16 treatedmiddle

P_6 untreatedmiddle

P_5 untreatedmiddle

P_25 treatedmiddle

wat

er le

vel a

bov

e th

ere

stri

ctiv

e la

yer(

m)

B

0.000.501.001.502.002.503.00

P_1 saturation

P_2 untreatedbottom

p_19 treatedbottom

P_23 treatedbottom

wat

erle

vela

bov

eth

ere

stri

ctiv

ela

ayer

(m)

C

21

Figure 11: The relative depth of water table vs. gully depths in the selected gullies (gully I, gully II and gully III) at the points where short term Gully evolution measurement were taken place during the end of the rainy season.

3.433.04 3.40

2.682.60 2.28 2.00 1.69

0.000.501.001.502.002.503.003.504.00

0.00

1.00

2.00

3.00

4.00

P_19 P_21 P_23 P_24 Av.gullydepth(m)

 Depth ofwater table(m)

Gully I

Gully depth to the top of the watershed

A

0.00

1.00

2.00

3.00

4.00

0.00

1.00

2.00

3.00

4.00

P_11 P_12 P_13 P_17 P_18

Av.gullydepth(m)

Gully II

gully depth to top of the watershed 

B

0.00

1.00

2.00

3.00

4.00

0.00

1.00

2.00

3.00

4.00

P_1 P_2 P_4 P_6 P_7 P_8

Av.gullydepth(m)

Gully III

Gully depth to the top of the watershed

C

22

Figure 12: Piping erosion occurring at the bottom part of the watershed during the month September first.

There was a direct correlation of water table and slumping. In the lower saturated part

of the watershed where the gullies came together the greatest slumping was observed

(Table 7 and Figure 7). In addition, frequent slumping of Gully walls and heads in the

middle treated part of the watershed prevail during August end and mid-September

where the rainfall duration within these days was relatively higher. As a result the soils

become saturated which could not resist the hydraulic pressure to stand and so that it

collapse. For example the piezometers P_21, 23 and 4 were installed in the middle of

the treated watershed where the area is relatively free from external obstruction both

from cultivation and free grazing. The plot area around this point has been used for

grass production which is usually harvested with hand to feed animals. In the area it

was observed that gully slumping was widespread. During the monitoring period the

saturated bottom area gully increased its dimension and retreats up its head cut where

the water table in the area was near the surface which is 2.57-1.79m above the gully

bottom in the period of August end to mid-September (Appendix 9).

23

Observations made during the study time and before as technical supervisor in the area

it was the overland flow coming from the side and above the gully usually joins the

gully through the cracks and voids. These tend to create a saturated condition below

the surface at the gully wall resulting in collapsing of the soil creating the big hole

(Figure 13).

Figure 13: Piping erosion occurring at the bottom part of the watershed.

Our results are in agreement with Poesen (1993), Fox et al (2007) and Stankovianski,

(2003) that gully banks are less affected by overland flow than by other processes such

as piping and mass movement as a result of a high water table. Our results are only

partly in agreement with Claessens et al. (2007) who reported that important

preparatory causal factor for landslides were: high rain fall, steep slopes, deforestation,

high weathering rates and slope material with low shear strength of high clay. The

slopes of the banks of the gully were steep, but the gullies formed in the flatter parts of

the landscape. The soils were sandy instead of clayey but they had low shear strength

due to saturation.

24

Table 7: Summary of the measured parameter average values and change in percentage of gullies; Gully, Gully, Gully and saturation bottom gully

3.4 Runoff

Runoff was measured with a rectangular weir at the outlet of Gullies I and II where

graded bunds were maintained and Gully III without any soil water conservation

structures in place. The storm flow patterns are similar for the three gullies with rapid

increase in stream flow after the rain starts and then a rapidly decline in discharge after

the rain stops. There are slight differences the runoff starts immediately for gullies I

and II while it usually delayed by five minutes for gully III. After the rainfall stops,

the discharge last only for an hour usually. The discharge begins a few minutes earlier

in Gully I and II than in Gully III. The short delay between runoff and rainfall is a

good indication that runoff is generated on the saturated areas. If infiltration runoff

would have occurred there would be a variable delay between the start of rainfall and

Variable Units

Gully I Gully II Beginning

of rainy season

End of rainy

season

Change in %

Beginning of rainy season

End of rainy

season

Change in %

ATW M 8.15 8.84 8.47 5.22 5.90 13.04 AMW M 5.20 5.82 11.85 3.43 4.46 30.11 ABW M 1.44 1.48 2.78 1.58 1.71 8.23 AD M 3.12 3.28 5.07 2.21 2.45 10.63

T. Vol. m3 13683.77 15685.45 14.77 5697.6 7310.72 30.49

Variable Units

Gully III Saturation bottom Beginning

of rainy season

End of rainy

season

Change in %

Beginning of rainy season

End of rainy

season

Change in %

ATW M 4.92 5.16 4.88 1.74 3.00 72.41 AMW M 3.88 4.25 9.31 1.94 3.10 59.79 ABW M 1.35 1.45 7.16 1.67 2.80 67.66 AD M 2.02 2.24 10.97 1.80 2.67 48.33

T. Vol. m3 6904.58 8189.21 18.61 8.38 51.26 511.69

25

runoff depending on the rainfall intensity. The saturated areas are larger, compact

shape and closer to the gully in the treated watershed (drained by Gullies I and II) than

for Gully III. This might explain slightly larger delay in runoff for Gully III.

The peak flow in Figure 15 shows that there is not a systematic difference in peak

flow when expressed on a hectare basis between the treated and untreated watersheds.

The peak flow values were smaller for Gullies I and II (draining an area of 5.0 ha)

than Gully III with a watershed area of 9.4 ha (Appendix 3 and 4).

Figure 14: Average monthly rainfall in 2010 in Warke watershed, where high rainfall was registered in the month June

3.4.1 Short term evolution of gully volume and soil erosion rate in the study watershed

FARMERS KONWLEGE ABOUT GULLY EROSION

Frequent field observations were made with farmers and guards where the soil was

saturated at the surface and at various locations along the gullies. These discussions

took the form of a question asked by the researcher that was answered by the farmers.

On the question “why do we observe gully sliding in this well treated area?” the

response was: “It is the water that infiltrate from there above that is coming out here

where the gully slumps”. Their understanding was correct as proven by the piezometer

050

100150200250300350400

monthlyrainfall

Rainfall(m

m)

26

readings and is opposite the general option that gullies are formed by fast flowing

water.

Figure 15: Time series Runoff discharge in the treated and untreated area; the figure shows only the runoff measured during the period mid July to September end where the measurement was undertaken.

The farmers responded on the question of timing of slumping of gully walls that

slumping was most severe during the first rainy weeks as a result of subsurface flow

moving through the cracks and causing local saturation near the banks. At the end of

July, cracks are usually close resulting in less frequent slumps. On the question why

aggregation of soils started in August, the response was quite brief in that it is a

common phenomenon. The farmers also are aware of the phenomenon that during the

27

first rainy months of June and July the sediment concentration is high. They explained

that during the dry months the soil becomes smooth and fine and then during the rainy

season become easily saturated by the rain after which it is easily carried away by

runoff.

Figure 16: Short term percentage volume evolution of the three selected gullies.

From the farmer’s answers to the questions asked, it becomes obvious that the farmers

are very knowledgeable about the erosion processes in the landscape. This shows that,

researchers and engineers can obtain valuable information of watershed erosion

processes by consulting the farmers first and based on that determine what erosion

practices are most effective.

0.00

100.00

200.00

300.00

400.00

500.00

600.00

Gully_1 Gully_2 Gully_3 Sat.Gully

Percent Change volume of selected gullies

Change in %

volume in

m3

28

Figure 17: Farm land where the three to four times tillage operations have been undertaken and prone to runoff erosion at the beginning of the rainy season. Actually what you can see is the interflow in plowed land that surfaces at the border where it becomes over

29

CHAPTER FOUR

4 Conclusions and Recommendations

4.1 Conclusions

In this thesis gully expansion in Warke watershed is studied. The Warke watershed is

located in the upper Blue Nile Basin, Ethiopia at an altitude between 2632- 2500 m.

The area has a humid monsoon climate with an average annual rainfall of 1300 mm.

According to informants, gully formation started thirty years ago after the area became

intensively cultivated and farm plots were demarcate/separate using traditional small

waterways (locally called Fesses) along the slope. Gullies have expanded continuously

since that time. Graded bunds and planting along the gullies were installed in the

whole watershed in the 1990’s to stop the gully expansion and were only maintained

in one part of the watershed where guards were hired.

Erosion rates since the initiation of the gullies were 22 t/ha/yr and 58 t/ha/yr for the

two gullies in the watershed with the conservation practices and 48 t/ha/yr for the

gully in the area without conservation practices. Short term soil loss rates were many

times greater indicating that these gullies were in their acceleration phase. Since

rainfall exceeds the evaporative demand of the crop a perched water table formed over

the restrictive layer during the rainy monsoon phase. The water table was generally

deeper in the upper watershed than at lower elevations where the slope decreased.

Active gully formation occurred in areas where the groundwater was above the gully

bottom. Since infiltration was in general greater than the prevailing rainfall intensities

and most of the rainfall infiltrated in the soil, gully function was caused by subsurface

flow and not by surface flow.

30

From the study it can be concluded that natural processes associated with more

intensive agriculture can accelerate the ongoing expansion of gullies. Similarly when

the climate becomes wetter it can also trigger new gullies in both cases because the

landscape is seeking for new equilibrium draining the excess water from the uplands

to the river. It has been well established that dryer climates will fill up gullies (Nyssen

et al, 2000).

4.2 Recommendations

The combination of structural and biological conservation measures that have shown

promising results in reducing infiltration excess should be improved further through

close technical support. It could be good to understand mechanisms for gully

expansion. Gully catchment should be improved with properly designed cutoff drains

so that weak points in gully head cut areas could be protected from overland flow,

while improving proper drainage structure in the treated mid-slope and bottom part of

the watershed could also reduce expansion rate. This can prevent the entrance of

overland runoff entering in the cracks. While, overland runoff diversion in divided

land plot areas into smaller pieces like in Warke watershed may be difficult for the

reason that the diverted overland flow could damage land in other area and promote

another new incisions in other parts. Hence, careful attention in selection and

designing should be given. Generally, before selection and design of any conservation

practices for land reclamation programs, due consideration should be given to the

ground water table elevation during the rainy phase of the monsoon.

In addition attempts should be made to reclaim the current gullies by gully plugs

consisting of sand bags and gabion check dams such as carried out in the Lenche Dima

watershed near Woldya. The reclaimed land should be planted with income producing

31

trees and the land should be divided among the young unemployed farmers so that that

the structures will be maintained.

32

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36

APPENDICES

Appendix 1: Example of a measured gully cross-section

Average width =

Where, WT= Top width,

WM=Middle width, WB = Bottom

width, d= depth

d1 2 3 4 5 ⋯

nd 0

Cross-sectional area(A)= Average depth*Average width, Gully Volume=A*L

The gully volume was estimated using the formula (example of measured gully cross-

section is described in Appendix 2.

ΣLiAi…………………………equation 1

Where Li is the length of considered gully segment (m) and Ai is the representative

cross sectional area of the gully segment (m2).

Long-term gully erosion rates (RL) in tone ha-1yr-1 were calculated using the equation:

…………………………equation 2

Where, V= estimated current volume of the gully (m3), Bd= average bulk density of

soils in the watershed, T= Time span of gully development in years, C= the watershed

area in hectares.

37

Cylindrical core sampler was used to take undisturbed soil samples from different

parts of the watershed to determine soil bulk density. Fifteen samples were collected at

the twenty-eight piezometer locations both in the treated and untreated parts of the

watershed. Samples were weighed before getting into a 1050C oven dry for 24 hours

and weighed after dried. The mean of the total samples was taken as the bulk density

for the soil in the study area.

Short-term erosion rates Rs in t ha-1 yr-1 were determined to estimate the erosion rate

in the study period.

……………………….equation 3

Where V= Gully volume at the end of study period, VO=Initial gully volume at the

beginning of the study period.

Erosion per unit gully surface (RP), in tone m-2 was determined by the formula:

…………………………equation 4

Where V= the current volume of the gully, AP= Plane area of the gully (m2).

38

Appendix 2: Short term evolution of the three considered gullies measured at the beginning and end of rainy season

Beginning of rainy season End of rainy season

Width Depth

L (m) volume

(m3)

Width Depth

L (m)

volume (m3)

DS R

TW (m)

MW ( m)

BW (m)

AW (m)

LS (m)

M (m)

RS (m)

AD (m)

TW (m)

MW (m)

BW (m)

AW (m)

LS (m)

M (m)

RS (m)

AD (m)

G I

A 7.00 5.00 1.70 4.57 2.60 5.70 2.00 3.43 11.50 6.70 1.70 6.63 2.70 6.30 2.20 3.73

B 8.80 5.80 1.20 5.27 2.20 4.80 2.13 3.04 7.45 5.60 1.40 4.82 2.20 3.80 2.20 2.73

C 10.80 6.70 1.80 6.43 2.60 4.60 3.00 3.40 9.10 6.28 1.80 5.73 2.90 5.30 3.00 3.73

D 7.95 4.50 1.30 4.58 2.50 3.70 2.90 3.03 7.95 5.50 1.30 4.92 2.60 5.00 3.00 3.53

E 6.20 4.00 1.20 3.80 2.15 3.80 2.10 2.68 8.20 5.00 1.20 4.80 2.15 3.70 2.10 2.65

Mean 8.15 5.20 1.44 4.93 2.41 4.52 2.43 3.12 890 13683.8 8.84 5.82 1.48 5.38 2.51 4.82 2.50 3.28 890 15685. 5

G II

A 6.30 3.00 1.40 3.57 2.00 4.50 1.30 2.60 6.20 4.70 2.00 4.30 2.14 2.90 1.40 2.15

B 7.50 5.40 2.60 5.17 2.45 3.60 2.77 2.94 7.50 5.40 1.50 4.80 2.68 5.00 2.90 3.53

C 3.50 2.54 1.60 2.55 1.90 2.10 1.75 1.92 7.00 6.00 1.60 4.87 1.90 3.45 1.90 2.42

D 6.00 4.00 1.30 3.77 1.90 2.50 1.84 2.08 6.00 4.00 1.30 3.77 2.15 3.55 1.95 2.55

E 2.78 2.20 1.00 1.99 1.00 2.31 1.30 1.54 2.78 2.20 1.00 1.99 1.20 2.40 1.30 1.63

Mean 5.22 3.43 1.58 3.41 1.85 3.00 1.79 2.21 754.9 5697.6 5.90 4.46 1.48 3.95 2.01 3.46 1.89 2.45 754.9 7310.7

G III

A 1.70 1.50 1.30 1.50 1.10 1.00 1.00 1.03 2.30 3.00 1.50 2.27 1.10 1.50 1.00 1.20

B 4.00 2.60 1.80 2.80 1.70 2.20 1.20 1.70 4.30 2.74 1.80 2.95 1.70 3.20 1.20 2.03

C 7.00 5.00 1.40 4.47 1.73 4.20 1.80 2.58 7.10 5.20 1.58 4.63 1.73 3.14 1.80 2.22

D 6.60 5.80 1.60 4.67 1.70 3.50 1.70 2.30 6.80 6.10 1.80 4.90 1.70 3.20 1.70 2.20

E 6.20 5.40 1.00 4.20 2.64 2.42 2.80 2.62 6.20 5.43 1.00 4.21 2.64 5.20 2.80 3.55

F 4.00 3.00 1.00 2.67 1.90 2.13 1.65 1.89 4.24 3.00 1.00 2.75 1.90 3.20 1.65 2.25

Mean 4.92 3.88 1.35 3.38 1.80 2.58 1.69 2.02 1010 6904.6 5.16 4.25 1.45 3.62 1.80 3.24 1.69 2.24 1010 8189.2

38

39

Appendix 3: Surface Runoff Discharge in the Untreated Area (measured under weir_1)

Date

Time taken by

the floater

(seconds)

Depth of

flow (m)

Velocity (d/t)

m/s

Flow

area

Discharge

(Q=A.V) m3/s

Discharge Qm3/hr

Q m3/hr/h

a

31-Jul-10 14 0.43 0.7 0.5 0.35 1264 135.0 2-Aug-10 18 0.21 0.6 0.2 0.14 493 52.6 7-Aug-10 22 0.05 0.4 0.1 0.03 94 10.1 8-Aug-10 14 0.08 0.7 0.1 0.06 231 24.6 11-Aug-10 11 0.35 0.9 0.4 0.36 1313 140.3 13-Aug-10 21 0.06 0.5 0.1 0.03 122 13.1 15-Aug-10 12 0.43 0.8 0.5 0.41 1469 156.9 22-Aug-10 46 0.41 0.2 0.5 0.10 373 39.8 23-Aug-10 55 0.15 0.2 0.2 0.03 117 12.5 25-Aug-10 40 0.05 0.3 0.1 0.01 53 5.6 27-Aug-10 13 0.43 0.8 0.5 0.40 1430 152.8 29-Aug-10 45 0.03 0.2 0.0 0.01 31 3.3 31-Aug-10 43 0.04 0.2 0.0 0.01 39 4.2 1-Sep-10 40 0.05 0.3 0.1 0.02 56 6.0 7-Sep-10 13 0.36 0.8 0.4 0.33 1197 127.9 8-Sep-10 15 0.35 0.7 0.4 0.28 996 106.4 9-Sep-10 17 0.05 0.6 0.1 0.03 116 12.4

15-Sep-10 19 0.16 0.5 0.2 0.10 362 38.7 16-Sep-10 19 0.41 0.5 0.5 0.25 909 97.1 22-Sep-10 16 0.31 0.6 0.4 0.22 799 85.4 mean 57.4 contributing area= 9.36 ha weir dimensions height 0.45 width 1.17 cross-sectional area 0.53

40

Appendix 4: Surface Runoff Discharge in the Treated Area (measured under weir_2)

Date

Time taken by

the floater seconds

(s)

depth of

flow m

velocity (d/t)

m/s

flow area

(A) m2

Discharge (Q = AV)

m3/s

Q m3/h

r

Q m3/hr/ha

2-Aug-10 33.33 0.36 0.3 0.2 0.05 165 32.8 7-Aug-10 43.48 0.25 0.2 0.1 0.02 88 17.4 8-Aug-10 19.00 0.23 0.5 0.1 0.05 185 36.7 11-Aug-10 13.33 0.38 0.9 0.2 0.15 522 103.8 13-Aug-10 55.56 0.20 0.2 0.1 0.02 55 10.9 15-Aug-10 14.08 0.45 0.9 0.2 0.17 618 122.9 22-Aug-10 76.92 0.26 0.1 0.1 0.01 52 10.3 23-Aug-10 76.92 0.29 0.1 0.1 0.02 58 11.4 25-Aug-10 43.00 0.05 0.2 0.0 0.00 18 3.5 27-Aug-10 15.00 0.37 0.7 0.2 0.10 377 74.9 29-Aug-10 44.00 0.05 0.2 0.0 0.00 17 3.4 31-Aug-10 42.00 0.06 0.2 0.0 0.01 22 4.3 1-Sep-10 37.00 0.04 0.3 0.0 0.00 17 3.3 7-Sep-10 13.00 0.35 0.8 0.1 0.11 411 81.7 8-Sep.10 14.00 0.43 0.8 0.2 0.15 525 104.4 9-Sep-10 21.74 0.35 0.5 0.1 0.07 267 53.1

15-Sep-10 43.48 0.32 0.2 0.1 0.03 112 22.3 16-Sep-10 15.00 0.36 0.9 0.2 0.17 626 124.5 22-Sep-10 14.00 0.40 0.9 0.2 0.15 531 105.6

mean 246 48.8

contributing area= 5.03 ha weir dimensions

height 0.4 width 1.06 cross-

sectional area

0.42

41

Appendix 5: Measurements and observations undertaken at different parts of the watershed for the identification and determination: gully incision and expansion factors.

42

Apendix 6: Figures at the top part of the watershed; left side before 9years, right side after reclamation. Birara was working there in the district. The result seems good at the top part of the watershed while, gullies are expanding at middle of the watershed due to subsurface flow and ground water push effect in the bottom saturation area.

43

Appendix 7: Figures at the bottom outlet of the watershed showing gully slides due to subsurface water rise up to the surface and soils saturation.

44

Appendix 8: Observed Gully incision due to subsurface water flow in the middle treated area of gully_1 and outlet bottom saturated area of the watershed.

45

Appendix 9: Daily recorded water table depth (m) in Warke watershed from July to October 2010.

date P1 P2 P19 P20 P16 P18 P15 P17 P21 P22 P23 P24 P25 P26 P27 P28 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14

28-Jul 1 2.3 1.3 2.26 1.37 1.53 2.85 1.77 1.86 1.29 1.21 1.17 2.14 1.37 1.59 1.47 1.38 0.51 1.35 2.2 3.15 1.83 3.31 3.51 3.55 1.86 2.95 3.7

29-Jul 0.94 2.4 1.39 2.24 1.35 1.49 2.8 1.76 1.89 1.49 1.12 1.23 2.13 1.36 1.59 1.46 1.39 0.85 1.6 2.3 3.4 1.84 3.34 3.54 3.59 1.86 2.94 3.69

30-Jul 0.7 2.4 1.55 2.23 1.48 1.67 2.91 1.87 1.86 1.69 1.81 1.28 2.15 1.37 1.6 1.45 1.47 0.75 2.15 2.55 3.6 1.84 3.4 3.55 3.6 1.85 3.11 3.64

31-Jul 0.48 2.4 2.73 2.32 1.89 2.48 2.87 2.12 2.12 2.49 2.05 1.47 2.45 1.37 1.59 1.45 1.32 1.48 2.45 2.8 3.6 1.85 3.4 3.55 3.6 1.86 3.11 3.64

1-Aug 0.35 2.11 1.7 1.87 1.64 2.13 2.57 1.69 2.08 2.22 1.99 1.36 1.92 1.22 1.59 1.08 0.96 1.44 2.3 2.3 3.6 1.89 3.4 3.55 3.6 1.84 3.14 3.63

2-Aug 0.55 2.26 1.96 2 1.59 1.92 2.71 1.84 2.08 2.71 1.97 1.44 1.91 1.29 1.59 1.2 0.96 1.38 2.4 2.4 3.6 1.87 3.4 3.55 3.6 1.86 3.13 3.76

3-Aug 0.43 2.34 2.3 2.06 1.61 2.35 2.83 1.98 2.09 2.7 1.76 1.56 2.13 1.33 1.57 1.23 0.99 1.58 2.3 2.5 3.59 1.87 3.4 3.55 3.6 1.86 3.12 3.67

4-Aug 0.45 2.29 2.53 2.16 1.81 2.39 2.83 2.06 2.08 2.85 1.98 1.55 2.19 1.37 1.6 1.31 1.16 1.62 2.2 2.5 3.59 1.89 3.4 3.55 3.6 1.87 3.17 3.74

5-Aug 0.49 2.4 2.69 2.22 1.88 2.49 2.85 2.09 2.12 2.79 2.04 1.56 2.33 1.36 1.58 1.36 1.18 1.62 2.1 2.7 3.59 1.89 3.4 3.55 3.6 1.84 3.14 3.76

6-Aug 0.51 2.42 2.81 2.4 1.9 2.59 2.91 2.12 2.1 2.84 2.04 1.71 2.4 1.37 1.6 1.39 1.17 1.77 2.15 2.75 3.58 1.88 3.4 3.55 3.6 1.87 3.18 3.74

7-Aug 0.59 2.41 2.84 2.58 1.9 2.69 2.96 2.13 2.19 2.96 2.04 1.76 2.45 1.37 1.6 1.4 1.25 1.74 2.15 2.7 3.59 1.89 3.4 3.55 3.6 1.87 3.2 3.77

8-Aug 0.52 2.44 2.84 2.69 1.9 2.74 2.98 2.13 2.01 2.96 2.05 1.74 2.45 1.37 1.6 1.4 1.2 1.78 2.1 2.55 3.59 1.89 3.4 3.55 3.6 1.87 3.19 3.76

9-Aug 0.48 2.37 2.26 2.45 1.89 2.77 2.96 2.09 2.17 2.95 2.04 1.73 2.39 1.38 1.6 1.4 1.3 1.81 2.83 2.96 3.59 1.89 3.4 3.55 3.6 1.87 3.18 3.77

10-Aug 0.56 2.42 2.64 2.41 1.89 2.84 3.01 2.09 2.49 2.97 2.05 1.72 2.48 1.36 1.59 1.41 1.34 1.84 2.82 2.97 3.59 1.89 3.4 3.55 3.6 1.87 3.19 3.78

11-Aug 0.6 2.42 2.85 2.46 1.89 2.68 3.04 2.1 2.45 2.97 2.05 1.73 2.37 1.37 1.6 1.4 1.25 1.82 2.82 2.97 3.59 1.89 3.4 3.55 3.6 1.86 3.19 3.78

12-Aug 0.62 2.4 2.74 2.43 1.88 2.68 3.05 2.11 2.45 2.98 2.05 1.74 2.38 1.37 1.6 1.4 1.28 1.82 2.83 2.97 3.59 1.89 3.4 3.55 3.6 1.86 3.19 3.78

13-Aug 0.72 2.43 2.72 2.42 1.88 2.68 3.07 2.13 2.48 3.02 1.97 1.74 2.38 1.37 1.6 1.4 1.41 1.88 2.82 2.97 3.59 1.89 3.4 3.55 3.6 1.86 3.19 3.78

14-Aug 0.66 2.39 2.58 2.39 1.77 2.71 3.08 2.13 2.45 2.97 2.01 1.75 2.36 1.38 1.59 1.4 1.53 1.88 2.82 2.97 3.59 1.89 3.4 3.55 3.6 1.87 3.2 3.77

15-Aug 0.68 2.41 2.65 2.36 1.62 2.68 3.1 2.13 2.45 2.99 2.01 1.75 2.32 1.37 1.6 1.39 1.59 1.88 2.83 2.97 3.59 1.89 3.4 3.55 3.6 1.87 3.19 3.78

16-Aug 0.64 2.28 2.04 2.06 1.53 2.56 2.99 2.03 2.5 2.73 2.04 1.75 2.29 1.37 1.6 1.39 1.66 1.84 2.83 2.96 3.59 1.89 3.4 3.55 3.6 1.87 3.18 3.78

17-Aug 0.78 2.38 2.4 2.04 1.45 2.23 2.94 1.88 2.46 2.82 2.04 1.75 1.94 1.38 1.6 1.39 1.66 1.87 2.82 2.97 3.59 1.89 3.4 3.55 3.6 1.87 3.17 3.78

18-Aug 0.69 2.4 2.54 2.06 1.56 2.41 3.03 2.02 2.37 2.95 1.98 1.74 2.12 1.37 1.6 1.4 1.67 1.87 2.82 2.97 3.59 1.89 3.4 3.55 3.6 1.87 3.17 3.78

19-Aug 0.67 2.41 2.7 2.14 1.65 2.6 3.11 2.14 2.32 2.94 1.99 1.72 2.33 1.38 1.6 1.41 1.67 1.88 2.82 2.98 3.59 1.89 3.4 3.55 3.6 1.87 3.19 3.78

20-Aug 0.77 2.45 2.72 2.35 1.86 2.67 3.18 2.15 2.4 2.98 2.04 1.73 2.36 1.37 1.6 1.41 1.68 1.85 2.83 2.98 3.59 1.89 3.4 3.55 3.6 1.87 3.2 3.78

21-Aug 0.86 2.48 2.75 2.47 1.87 2.71 3.19 2.16 2.41 2.99 2.04 1.73 2.36 1.38 1.6 1.42 1.69 1.87 2.82 2.98 3.59 1.89 3.4 3.55 3.6 1.87 3.2 3.78

22-Aug 0.7 2.43 2.88 2.54 1.86 2.78 3.19 2.15 2.41 3.01 2.05 1.75 2.35 1.37 1.6 1.46 1.67 1.88 2.82 2.97 3.59 1.89 3.4 3.55 3.6 1.87 3.2 3.78

23-Aug 0.68 2.42 2.79 2.55 1.82 2.89 3.21 2.14 2.47 3 2.04 1.73 2.41 1.36 1.6 1.38 1.67 1.88 2.83 2.98 3.59 1.9 3.4 3.55 3.6 1.87 3.2 3.78

24-Aug 0.79 2.4 2.7 2.55 1.85 2.87 3.21 2.15 2.51 2.99 2.04 1.75 2.35 1.38 1.61 1.41 1.69 1.88 2.83 2.98 3.59 1.9 3.4 3.55 3.6 1.87 3.22 3.77

25-Aug 1.14 2.41 2.83 2.51 1.81 2.88 3.22 2.14 2.5 2.95 2.04 1.75 2.5 1.38 1.61 1.44 1.69 1.89 2.83 2.98 3.59 1.9 3.4 3.55 3.6 1.87 3.2 3.76

26-Aug 0.78 2.37 2.71 2.43 1.66 2.9 3.22 2.13 2.45 2.95 2.03 1.73 2.42 1.36 1.6 1.34 1.68 1.89 2.74 2.98 3.59 1.9 3.4 3.55 3.6 1.87 3.18 3.78

27-Aug 0.78 2.34 2.12 2.15 1.62 2.91 3.22 2.02 2.4 2.86 2.04 1.74 2.36 1.35 1.58 1.34 1.7 1.89 2.72 2.98 3.59 1.9 3.4 3.55 3.6 1.88 3.18 3.77

28-Aug 0.85 2.33 2.44 2.06 1.68 2.34 3.22 2.02 2.15 2.92 2.05 1.73 2.27 1.36 1.6 1.34 1.66 1.89 2.76 2.99 3.59 1.9 3.4 3.55 3.6 1.88 3.18 3.77

29-Aug 0.8 2.33 2.5 2.01 1.82 2.42 3.22 2.12 1.94 2.96 2.03 1.69 2.24 1.37 1.59 1.37 1.66 1.89 2.78 3 3.59 1.9 3.4 3.55 3.6 1.88 3.18 3.77

45

46

date P1 P2 P19 P20 P16 P18 P15 P17 P21 P22 P23 P24 P25 P26 P27 P28 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14

30-Aug 0.87 2.42 2.68 2.23 1.89 2.57 3.22 2.13 2.08 3 2.03 1.72 2.35 1.36 1.59 1.38 1.72 1.89 2.79 3 3.58 1.9 3.4 3.55 3.6 1.89 3.18 3.76

31-Aug 0.93 2.38 2.69 2.11 1.95 2.57 3.22 1.95 2.11 3 2.03 1.71 2.27 1.37 1.59 1.36 1.75 1.87 2.79 3 3.58 1.89 3.4 3.55 3.6 1.89 3.19 3.77

1-Sep 0.86 2.25 2.04 1.84 1.51 2.33 3.22 1.67 2 2.66 2.03 1.62 1.8 1.36 1.59 1.33 1.65 1.83 2.8 2.99 3.57 1.9 3.4 3.55 3.6 1.89 3.19 3.77

2-Sep 0.9 2.33 2.36 1.91 1.87 2.34 3.22 1.91 1.97 2.86 2.03 1.62 1.83 1.36 1.58 1.35 1.64 1.84 2.82 2.99 3.57 1.9 3.4 3.55 3.6 1.89 3.2 3.77

3-Sep 1.1 2.38 2.55 2.14 1.89 2.52 3.22 2.13 2.15 2.93 2.04 1.64 2.12 1.38 1.6 1.35 1.68 1.88 2.85 2.99 3.55 1.9 3.4 3.55 3.6 1.89 3.22 3.77

4-Sep 1.31 2.44 2.66 2.3 1.91 2.68 3.22 2.11 2.22 2.98 2.04 1.69 2.27 1.38 1.6 1.39 1.66 1.89 2.85 2.99 3.56 1.9 3.4 3.55 3.6 1.89 3.21 3.77

5-Sep 1.22 2.44 2.8 2.48 1.93 2.76 3.22 2.09 2.23 3 2.04 1.73 2.42 1.38 1.6 1.39 1.65 1.89 2.85 2.99 3.57 1.9 3.4 3.55 3.6 1.89 3.21 3.77

6-Sep 0.88 2.41 2.84 2.59 1.88 2.88 3.22 2.11 2.17 2.97 2.04 1.74 2.36 1.36 1.59 1.37 1.61 1.89 2.87 2.99 3.56 1.9 3.4 3.55 3.6 1.89 3.22 3.77

7-Sep 0.97 2.39 2.81 2.6 1.89 2.9 3.22 2.08 2.09 2.98 2.04 1.74 2.3 1.36 1.59 1.37 1.65 1.89 2.88 2.99 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.77

8-Sep 0.96 2.32 2.22 2.21 1.78 2.84 3.22 2.08 2.03 2.99 2.03 1.72 2.16 1.37 1.59 1.36 1.67 1.89 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.77

9-Sep 0.94 2.32 2.47 2.17 1.85 2.61 3.22 2.12 2.03 3.01 2.03 1.74 2.15 1.38 1.59 1.4 1.48 1.89 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.77

10-Sep 0.98 2.38 2.6 2.27 1.91 2.67 3.22 2.11 2.03 3.01 2.04 1.75 2.14 1.4 1.6 1.4 1.48 1.89 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.77

11-Sep 1.11 2.43 2.82 2.5 1.88 2.75 3.22 2.11 2.19 3.01 2.04 1.74 2.25 1.41 1.59 1.37 1.48 1.9 2.88 3 3.56 1.9 3.4 3.55 3.6 1.89 3.22 3.77

12-Sep 1.31 2.48 2.89 2.59 1.85 2.82 3.22 2.13 2.28 3.02 2.04 1.74 2.3 1.42 1.6 1.36 1.51 1.9 2.88 3 3.56 1.9 3.4 3.55 3.6 1.89 3.22 3.78

13-Sep 1.23 2.48 2.65 2.47 1.87 2.93 3.22 2.15 2.34 3 2.03 1.61 2.4 1.42 1.59 1.36 1.58 1.9 2.79 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.79

14-Sep 1.04 2.4 2.6 2.46 1.71 2.93 3.22 2.15 2.08 2.99 2.03 1.74 2.12 1.42 1.59 1.35 1.44 1.9 2.87 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.79

15-Sep 1.23 2.43 2.66 2.46 1.72 2.94 3.22 2.15 2.24 3.01 2.04 1.74 2.42 1.42 1.59 1.4 1.49 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.79

16-Sep 1.03 2.31 2.64 2.32 1.75 2.88 3.22 2.15 2.23 3.01 2.02 1.74 2.4 1.42 1.58 1.41 1.47 1.9 2.87 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.79

17-Sep 1.02 2.34 2.51 2.23 1.8 2.72 3.22 2.16 2.21 3.02 2.03 1.73 2.38 1.42 1.59 1.41 1.49 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.8

18-Sep 0.95 2.37 2.64 2.35 1.79 2.57 3.22 2.16 2.2 3.02 2.03 1.75 2.31 1.42 1.59 1.4 1.49 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.8

19-Sep 1.03 2.43 2.71 2.52 1.86 2.8 3.22 2.15 2.35 3.02 2.04 1.74 2.4 1.42 1.59 1.41 1.54 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.8

20-Sep 1.19 2.43 2.97 2.64 1.88 2.87 3.22 2.16 2.48 3.02 2.04 1.74 2.44 1.42 1.58 1.41 1.53 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

21-Sep 0.99 2.44 2.83 2.68 1.87 2.87 3.22 2.16 2.25 2.99 2.03 1.74 2.44 1.42 1.58 1.39 1.52 1.9 2.87 3 3.56 1.9 3.4 3.55 3.6 1.89 3.23 3.8

22-Sep 1.05 2.46 2.79 2.74 1.81 2.91 3.22 2.16 2.38 3 2.03 1.74 2.45 1.42 1.58 1.39 1.51 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

23-Sep 1.14 2.48 2.94 2.8 1.73 2.96 3.22 2.15 2.49 3 2.03 1.73 2.42 1.41 1.59 1.38 1.51 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

24-Sep 1.04 2.51 3.01 2.87 1.82 2.98 3.22 2.15 2.56 3.02 2.04 1.75 2.44 1.39 1.59 1.4 1.55 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

25-Sep 1.04 2.43 2.33 2.77 1.82 3.03 3.22 2.15 2.55 2.99 2.04 1.76 2.38 1.38 1.58 1.39 1.6 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

26-Sep 1.12 2.3 2.47 2.44 1.82 3.03 3.22 2.15 2.39 3 2.04 1.74 2.44 1.38 1.58 1.41 1.59 1.9 2.88 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

27-Sep 1.13 2.41 2.77 2.49 1.83 3.02 3.22 2.16 2.44 3 2.04 1.74 2.45 1.4 1.59 1.41 1.59 1.9 2.89 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.8

28-Sep 1.13 2.86 2.89 2.58 1.83 2.99 3.22 2.16 2.47 3.02 2.04 1.75 2.46 1.4 1.59 1.4 1.6 1.9 2.89 3 3.57 1.9 3.4 3.55 3.6 1.89 3.09 3.8

29-Sep 1.09 2.53 2.95 2.63 1.82 2.95 3.22 2.16 2.53 3.02 2.04 1.75 2.45 1.4 1.59 1.4 1.6 1.9 2.89 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

30-Sep 1.01 2.54 3.07 2.73 1.8 2.92 3.22 2.16 2.57 3.02 2.04 1.75 2.44 1.4 1.59 1.4 1.55 1.9 2.89 3 3.57 1.9 3.4 3.55 3.6 1.89 3.22 3.8

1-Oct 1.05 2.57 3.14 2.85 1.83 3.02 3.22 2.16 2.57 3.02 2.04 1.75 2.46 1.41 1.59 1.4 1.6 1.9 2.89 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

2-Oct 1.11 2.55 3.16 2.9 1.85 3.05 3.22 2.16 2.47 3.02 2.05 1.75 2.46 1.41 1.59 1.4 1.33 1.9 2.89 3 3.57 1.9 3.4 3.55 3.6 1.89 3.23 3.8

3-Oct 1.07 2.52 3.18 2.91 1.88 3.06 3.22 2.16 2.42 3.03 2.05 1.76 2.47 1.41 1.59 1.4 1.51 1.9 2.89 3 3.56 1.9 3.4 3.55 3.6 1.89 3.23 3.8

4-Oct 1.06 2.54 3.23 2.92 1.91 3.07 3.22 2.16 2.91 3.29 2.31 2.02 2.73 1.67 1.84 1.65 1.53 1.9 2.89 3 3.57 1.9 3.4 3.55 3.6 1.89 3.24 3.8

46

47

date P1 P2 P19 P20 P16 P18 P15 P17 P21 P22 P23 P24 P25 P26 P27 P28 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14

Avg depth

of water table from

surface

0.87 2.41 2.6 2.4 1.78 2.67 3.12 2.08 2.28 2.88 2 1.69 2.31 1.38 1.59 1.38 1.5 1.79 2.72 2.91 3.57 1.89 3.4 3.55 3.6 1.88 3.19 3.77

Elev of bottom piezom 25

10

2513

2532

2536

2553

2540

2565

2550

2540

2545

2549

2555

2554

2562

2578

2571

2520

2535

2565

2573

2585

2600

2611

2617

2610

2589

2580

2575

Elev. of avg water table

2512

2514

2533

2538

2554

2541

2566

2551

2542

2546

2551

2555

2555

2563

2578

2572

2520

2535

2565

2573

2585

2600

2611

2617

2610

2589

2580

2575

47

48

Appendix10: Questionnaire for the study Gully formation and expansion Characteristics in the high lands of Blue Nile basin, Ethiopia.

Part I Date: _________ Persons present at survey meeting: Gender: M____ F____ Education Level: Uneducated: ___ Educated: Elementary school: ______ High school: _____ College: _____ Other: ______ 1. What are the major crops you have been using to your farmland? --------------------

--------------------------------------------------------------------------------------------------- 2. Is there a major change in cropping pattern during the last 15 years? If yes what

are the reasons? --------------------------------------------------------------------------------------------------------------------------------------------------------

3. How does change in cropping pattern affect soil erosion? -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

4. Do you have a problem of erosion in your farm? ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

5. How do you know soil erosion occurs on your farm land? (Indicators)---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------- 6. What are the noticeable changes in your farm land over time in:

Soil fertility / crop productivity / fertilizer response ---------------------------- --------------------------------------------------------------------------------------------------- Intensity of rill erosion ------------------------------------------------------------------ --------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------- Soil depth/surface stoniness ----------------------------------------------------------- --------------------------------------------------------------------------------------------------- Runoff generation /infiltration/ water holding capacity ------------------------ --------------------------------------------------------------------------------------------------

7. From where dose the major runoff that cause soil erosion in your farm come from? ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

49

8. How do you protect your farmland from erosion? (yes/no) (List all methods you are applying) ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

9. Are methods you applying effective? -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

10. How do you measure the effectiveness of SWC measure? ---------------------------------------------------------------------------------------------------

11. Do you know about SWC technologies? ---------------------------------------------------------------------------------------------------

12. Have you ever participated in SWC technology demonstration, field days or workshops before? ----------

13. Do you have information on use of different SWC practices / technologies? If yes, state the advantages and disadvantages.

Advantages ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Disadvantages --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

14. Do you apply SWC on your whole farm? If no, how do you select a farm plot for SWC treatment? ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

15. In your opinion, what should be done to improve the effectiveness of SWC measure? ---------------------------------------------------------------------------------------------------

16. Do you apply fertilizer to your farmland--------------If yes, since when? ---------------------------------------------------------------------------------------------------

17. What level of yield advantage you would expect from fertilizer addition? Without fertilizer-------------------------------------------------------------------------- With fertilizer-----------------------------------------------------------------------------. Yield addition in% ------------------------------------

18. Do you expect the yield advantage would remain the same amount with the same

quantity of fertilizer of the next 5 years? ..................10 years? ……………… What was the trend over the past? Part II Erosion and its Relation with Runoff 19. Is erosion a problem in your area? (Yes/No) If yes, how serious it is? (Very severe/

medium level problem/ little problem) 20. Compared to other years is there more or less erosion this year? 21. How do you know as erosion exists (indicators of erosion problem)? 22. When, week of month, erosion mostly starts? What are the reasons? 23. When, week of month is erosion severe? Why?

50

24. Where (at which part of the watershed) erosion starts (Upper watershed / middle watershed/ bottom (level slope) of the watershed). Why?

25. Where do you think is erosion severe? Slope: (Upper watershed/ middle watershed/bottom watershed (level slope) parts) Why? Direction? Why? Land Use? Why? Soil Depth? Why? Soil Type? Why? Extent of saturation? Why? Conservation Structures? What other factors affect runoff generation?

26. What are the major causes of soil loss in the watershed? Rank the causes based on their severity? lack of conservation structures steep land without conservation structures damaged conservation structures lack of diversion ditch the land is under steep ridges others

27. Specific characteristics of the locations that produce most erosion? 28. Which type of erosion is dominant in the area? (Splash/Sheet/Rill/Gully) 29. Do you see any relationship between runoff and soil loss? (Yes/no) 30. If yes, when runoff usually carries much sediment? (Month and week) why? 31. From which Part of the watershed the runoff carry much sediment? (month and

week) (Upslope/ middle slope / bottom (level slope) of the watershed). 32. When this high runoff carries less sediment? (month and week) Why? 33. When streams usually carry much sediment? (month and week) Why? 34. Why do you think there is more sediment in the runoff water in the beginning of

the rainfall season than at the end? 35. What are the major crops you cultivate on your plot? List 36. How do you think crop types affect runoff generation and soil loss from cultivated

plots? (Is there a difference from crop to crop?) 37. Where in the watershed gully development starts? 38. Where in the watershed is gully density the highest? 39. Where is the oldest gully located in the watershed? 40. Where is the youngest gully located in the watershed? 41. Do you see any relationships between temporarily saturated areas and where gully

development starts? (Yes/No). If yes, explain their relation. 42. Is there anything else you would like to tell me about rainfall, runoff and erosion

in the watershed? Any questions I might have asked you that I didn’t?