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.
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.
iii
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.
iv
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.
v
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 vi
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 5 Conclusions and Recommendations ......................................................... 29 4.1 Conclusions ............................................................................................... 29 4.2 Recommendations ..................................................................................... 30 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 vii
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 viii
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 ix
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 x
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 xi
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
xii
GI: gully I
GII: gully II
GIII: gully III
GaSB: gully at saturation bottom
xiii
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
1
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
2
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.
3
CHAPTER TWO
2
2.1
MATERIALS AND METHODS
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
4
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
1996
1989
1983
2.2.1
Event
Land reform in the area
Down fall of farmers cooperatives association due to the policy
amendment by the Derg regime from socialism in to mixed economy
Organization of farmers’ cooperatives
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
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
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.
6
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)
P_1
P_2
P_19
P_20
P_16
P_18
P_15
P_17
P_21
P_22
P_23
P_24
P_25
P_26
P_27
P_28
P_3
P_4
P_5
P_6
P_7
P_8
P_9
P_10
P_11
P_12
P_13
P_14
2513
2516
2536
2540
2556
2544
2569
2553
2544
2549
2553
2557
2557
2564
2580
2573
2522
2537
2568
2576
2589
2602
2614
2621
2614
2591
2583
2579
Depth of
Piezometer
(m)
2.70
2.90
3.55
3.69
2.54
3.65
3.70
2.65
3.55
3.60
3.65
2.48
3.10
2.10
2.33
2.20
1.88
1.90
2.90
3.00
3.60
1.90
3.40
3.55
3.60
1.89
3.25
3.80
Average depth of
water table from
the surface (m)
0.87
2.41
2.60
2.40
1.78
2.67
3.12
2.08
2.28
2.88
2.00
1.69
2.31
1.38
1.59
1.38
1.50
1.79
2.72
2.91
3.57
1.89
3.40
3.55
3.60
1.88
3.19
3.77
7
Elevation of
Average Water
Table (masl)
2512.13
2513.59
2533.40
2537.60
2554.22
2541.33
2565.88
2550.92
2541.72
2546.12
2551.00
2555.31
2554.69
2562.62
2578.41
2571.62
2520.50
2535.21
2565.28
2573.09
2585.43
2600.11
2610.60
2617.45
2610.40
2589.12
2579.81
2575.23
Location in the
Watershed
Saturation bottom
″
Treated bottom
″
Treated middle
″
Treated top
Treated middle
″
″
Treated middle
″
″
″
Treated top
″
Untreated bottom
″
Untreated middle
″
″
Untreated top
″
″
″
Untreated middle
″
″
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 shortterm 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.
8
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.
9
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)
10
CHAPTER THREE
3
3.1
RESULT AND DISCUSSION
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
GI
G II
G III
GaSB
Incision started
1980
1987
1987
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
11
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
12
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).
13
Beginning of
rainy season
(2010)
Description
Length (m)
Av. Depth (m)
Av. width (m)
Volume (m3)
plan area (m2)
Length (m)
Av. Depth (m)
Av. Width (m)
Volume (m3)
plan area (m2)
End of rainy
season (2010)
Evaluation Period
Table 4: The dimension of selected gullies measured beginning and end of one rainy
season.
Volume change in%
GI
890.0
3.1
4.9
13,683.8
7,253.5
890.0
3.3
5.4
15,685.5
7,867.6
G II
754.9
2.2
3.4
5,697.6
3,940.5
754.9
2.5
4.0
7,310.7
4,453.9
G III
1,010.0
2.0
3.4
6,904.6
4,969.2
1,010.0
2.2
3.6
8,189.2
5,211.6
GaSB
2.6
1.8
1.8
8.4
4.6
6.4
2.7
3.0
51.3
21.2
14.6
28.3
18.6
511.8
Total
26,294.3
31,236.6
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
Table 5: Long and short term rates of gully erosion in GI, G II and G III Warke
watershed
Variable
GI
G II
G III
GaSB
Total
Area
weighted
average
3.2
Gully
segment
Bulk
age
Vo
3
)
density
V
(m
estimated
(m3)
(g/cm3) by local
informants
(yr)
13684 15,685
1.23
30
5698
7,311
1.24
23
6905
8,189
1.25
23
8.
51
1.22
2
26,294 31,236
1.24
Catchment
area (ha)
19.50
Rs
RL
(t/ha/yr) (t/ha/yr)
29.6
6.8
9.4
3.5
83
292
172
15
22
58
48
9
49.29
68.2
16.80
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
15
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
Top
Top
Top
Middle
Middle
Middle
Bottom
Bottom
Infiltration rate ( mm/hr)
Treated part
Untreated part
144
136
549
216
430
160
198
153
281
185
293
472
23
23
115
115
16
Land use
Slope
cultivated
cultivated
cultivated
cultivated
cultivated
cultivated
cultivated
cultivated
19
19
19
9
9
9
3
3
Average soil Infiltration rate(mm/hr)
Infiltration rate at in the treated Vs untreated area at different location
600
Infiltration rate
treated part ( mm/hr)
500
400
300
200
Infiltration rate
untreated part
( mm/hr)
100
0
Topographical location
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
17
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.
18
Figure 9: Average groundwater table height and location of 28 piezometers. Locations
of gully slips are indicated by small triangles
19
water level above
the restrictive layer(m)
A
water level above the
restrictive layer(m)
B
water level above the
restrictive laayer(m)
C
1.20
1.00
0.80
0.60
0.40
0.20
0.00
P_10
untreated top
P_11
untreated top
P_15 treated
top
P_28 treated
top
2.00
P_16 treated
middle
1.50
1.00
P_6 untreated
middle
0.50
0.00
P_5 untreated
middle
P_25 treated
middle
3.00
2.50
2.00
1.50
1.00
0.50
0.00
P_1 saturation
P_2 untreated
bottom
p_19 treated
bottom
P_23 treated
bottom
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
A
0.00
1.00
2.00
3.00
4.00
Gully I
P_19
P_21
P_23
3.04
3.43
1.69
2.00
2.28
2.60
P_24
2.68
3.40
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
Av.gully
depth(m)
Depth of
water table
(m)
Gully depth to the top of the watershed
B
Gully II
P_11
P_12
P_13
P_17
P_18
0.00
1.00
2.00
3.00
4.00
0.00
1.00
2.00
3.00
4.00
Av.gully
depth(m)
gully depth to top of the watershed Gully III
C
P_1
P_2
P_4
P_6
P_7
P_8
0.00
1.00
2.00
3.00
4.00
0.00
1.00
2.00
3.00
4.00
Av.gully
depth(m)
Gully depth to the top of the watershed
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.
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).
22
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.
23
Table 7: Summary of the measured parameter average values and change in
percentage of gullies; Gully, Gully, Gully and saturation bottom gully
Variable
Units
ATW
AMW
ABW
AD
T. Vol.
M
M
M
M
m3
Variable
Units
ATW
AMW
ABW
AD
T. Vol.
M
M
M
M
m3
3.4
Beginning
of rainy
season
8.15
5.20
1.44
3.12
13683.77
Gully I
End of
rainy
season
8.84
5.82
1.48
3.28
15685.45
Gully III
Beginning
End of
of rainy
rainy
season
season
4.92
5.16
3.88
4.25
1.35
1.45
2.02
2.24
6904.58
8189.21
Change
in %
8.47
11.85
2.78
5.07
14.77
Change
in %
4.88
9.31
7.16
10.97
18.61
Gully II
Beginning End of
of rainy
rainy
season
season
5.22
5.90
3.43
4.46
1.58
1.71
2.21
2.45
5697.6
7310.72
Change
in %
13.04
30.11
8.23
10.63
30.49
Saturation bottom
Beginning End of
Change
of rainy
rainy
in %
season
season
1.74
3.00
72.41
1.94
3.10
59.79
1.67
2.80
67.66
1.80
2.67
48.33
8.38
51.26
511.69
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
24
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)
Rainfall (mm)
than Gully III with a watershed area of 9.4 ha (Appendix 3 and 4).
400
350
300
250
200
150
100
50
0
monthly
rainfall
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
25
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
26
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.
Percent Change volume of selected gullies
600.00
volume in m3
500.00
400.00
300.00
Change in %
200.00
100.00
0.00
Gully_1
Gully_2
Gully_3
Sat.Gully
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.
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
CHAPTER FOUR
4
4.1
Conclusions and Recommendations
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.
29
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
30
trees and the land should be divided among the young unemployed farmers so that that
the structures will be maintained.
31
5
REFERENCES
Bayabil, H.K., Tilahun, S., Collick, A.S., Yitaferu, B. and Steenhuis, T.S. (2010) ‘Are
run-off processes ecologically or topographically driven in the (sub) humid
Ethiopian highlands? The case of the Maybar watershed’, Ecohydrology3
Issue: 4 Special Issue: SI Pages: 457-466 DOI: 10.1002/eco.170.
Bekele, W., Drake, L. 2003. Soil and water conservation decision behavior of
subsistence farmers in the eastern highlands of Ethiopia: a case study of the
Hunde- Laftoarea. Ecological Economics 46, 437-451.
Bewket, W. and Sterk, G.2003. Assessment of soil erosion in cultivated fields using a
survey methodology for rills in the ChemogaWatershed, Ethiopia. Agriculture,
Ecosystems and Environment 97: 81-93.
Billi, P., and Dramis, F. 2001. Geomorphological investigation on Gully erosion in the
Rift Valley and the northern highlands of Ethiopia. Catena, volume 50:353368.
Casalí J., López J.J. and Giráldez J.V. 1999: Ephemeral gully erosion in southern
Navarra (Spain). Catena 36: 65-84.
Claessens L., Knapen A., Kitutu M.G., Poesen J., Deckers J.A. 2007:
ModellingLandslids, soil redistribution and yield of Landslids on the Ugandan
footslopes of Mount Elgon. Journal of Geomorphology 90(2007) 23-35.
Conway, D., and Hulme, M.1993. Recent Fluctuations in Precipitation and Runoff
over the Nile Sub-Basins and their impact on main Nile Discharge. Climatic
32
Research unit,School of Environmental Sciences, University East Angela,
Norwich NR4 7TJ,U.K.
Daba, S., Rieger, W. and Strauss, P.2003. Assessment of gully erosion in eastern
Ethiopia using photogrammetric techniques. Catena volume 50: 273-291.
FAO, 1995. Global and National soils and Terrain digital database (SOTER).
FDRE (Federal Democratic Republic of Ethiopia),2008. Sustainable Land
Management (SLM): Project Implementation Manual, Final. Addis Ababa.
Ethiopia
Fox, G.A., Wilson, G.V., Simon, A., Langenden, E.J., Akay, O. and Fuchs, J.W.2007.
Measuring Stream Bank Erosion due to Ground Water Seepage: Correlation to
bank pore water pressure, precipitation and stream stage. Earth Surface
Processes and Landforms 32, 1558-1573
Garzanti, G., Ando, S., Vezzoli, G., Megid, A.A.A., and Elkammar, A.2006: Petrology
of Nile River sands(Ethiopia and Sudan) Sediment Budgets and Erosion
Patterns, Earth planet, Sci.Lett.,252,327-341.
Herweg, K., Ludi, E., 1999. The performance of selected soil and water conservation
measures – case studies from Ethiopia and Eritrea. Catena 36(1/2), 99-114.
Hurni, H., 1988. Climate, soil and water: Degradation and Conservation for the
Resourcesin the Ethiopian highlands, Part2. Mountain Research and
Development 8, 2/3, 123-130.
33
Ibrahim, A.M.1984. Description, Hydrology, Control, and Utilization. Implementation
Division, Arab Authority for Agricultural Investment and Development,
Sudan.
Ireneusz M., 2006. Gully erosion dating by means of anatomical changes in exposed
roots (proboszezowicke plateau; southern Poland). Journal on methods and
applications of absolute chronology vol.25, pp 57-66.
Moges, A. and Holden, N.M. 2009. Land cover Change and gully development in the
Umbulo watershed, southern Ethiopia. Mountain Research and Development
29(3):265-276.BioOne.
Nyssen, J., Poesen, J., Veyret-picot, M., Moeyersons, J., Mitiku, H., Deckers, J.,
Dewit, J., Naudts, J., Teka, K., Govers,G. 2006. Assessment of gully erosion
rates through interviews and measurements: a case study from northern
Ethiopia. Earth Surface Processes and Landforms 31.167-185.
Nyssen, J., Moeyersons J., Tervuren, Deckers, J., Mitiku, H., Poesen, J., 2000. Vertic
movements and developments and developments of stone covers and gullies,
Tigray Highlands, Ethiopia. Z.Geomorph. N.E.44 (2):145-164.
Poesen, J., Nachtergaele J., Verstraeten G.and Valentin C. 2003. Gully erosion and
environmental change: importance and research needs. Catena 50:91-133.
Poeson, J. 1993. Gully typology and gully control measures in the European belt.
Farm Land Erosion: in temperate plains environment and Hills. Journal of
Elsevier Science.16: 221-239.
34
Soil Science Society of America, 1984. Glossary of soil science terms. Soil Science
Society of America, Madison. Wl.http:www.soils.org/sssaglass/.
Stankovianski M., 2003: Historical evolution of permanent gullies in the Myjava Hill
Land, Slovakia. Catena 51: 223-240.
Tebebu, T.Y., Abiy, A.Z., Zegeye, A.D., Dahlke, H.E., Easton, Z.M., Tilahun, S.A.,
Collick, A.S., Kidnau, S., Moges, S., Dadgari, F. and Steenhuis, T.S. (2010)
Surface and subsurface flow effect on permanent gully formation and upland
erosion near Lake Tana in the Northern Highlands of Ethiopia,Hydrol. Earth
Syst. Sci. Discuss., 7, pp 5235–5265, 2010 www.hydrol-earth-syst-scidiscuss.net/7/5235/2010/ doi:10.5194/hessd-7-5235-2010.
Valentin, C., Poesen, J., Li, Y., 2005. Gully erosion: Impacts, factors and control.
Catena 63, 232-153.
Vandekerckhove, L., Poesen, J., Oostwaoudwijdenes D.J. and de.Figuveireda T.,
2000: Topographical thresholds for ephemeral gully initiation in intensively
cultivated areas of the Mediterranean. Geomorphology, 33:271-293.
Wells, R.R., Alonso, C.V., Bennett, S.J., 2009. Morphodynamics of head cut
development
and
soil
erosion
Sci.Soc.Am.J.73, 521-530.
35
in
upland
concentrated
flows.
Soil
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
⋯
n
d 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 crosssection 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.
36
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).
37
Appendix 2: Short term evolution of the three considered gullies measured at the beginning and end of rainy season
Width
D
S R
TW
(m)
Beginning of rainy season
Depth
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)
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
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
4.50
1.30
6.20
4.00
1.20
3.80
2.15
3.80
2.10
2.68
I
Mean
8.15
5.20
1.44
4.93
2.41
4.52
2.43
3.12
A
6.30
3.00
1.40
3.57
2.00
4.50
1.30
B
7.50
5.40
2.60
5.17
2.45
3.60
C
3.50
2.54
1.60
2.55
1.90
G D
6.00
4.00
1.30
3.77
E
2.78
2.20
1.00
Mean
5.22
3.43
38
7.95
I
I
I
volume
(m3)
7.00
D
G
L (m)
A
G E
I
I
End of rainy season
Depth
Width
8.20
5.00
1.20
4.80
2.15
3.70
2.10
2.65
8.84
5.82
1.48
5.38
2.51
4.82
2.50
3.28
2.60
6.20
4.70
2.00
4.30
2.14
2.90
1.40
2.15
2.77
2.94
7.50
5.40
1.50
4.80
2.68
5.00
2.90
3.53
2.10
1.75
1.92
7.00
6.00
1.60
4.87
1.90
3.45
1.90
2.42
1.90
2.50
1.84
2.08
6.00
4.00
1.30
3.77
2.15
3.55
1.95
2.55
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
1.58
3.41
1.85
3.00
1.79
2.21
5.90
4.46
1.48
3.95
2.01
3.46
1.89
2.45
890
754.9
13683.8
5697.6
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
5.16
4.25
1.45
3.62
1.80
3.24
1.69
2.24
1010
6904.6
38
L
(m)
volume
(m3)
890
15685. 5
754.9
7310.7
1010
8189.2
Appendix 3: Surface Runoff Discharge in the Untreated Area (measured under
weir_1)
Date
Time
taken by
the
floater
(seconds
)
Depth
of
flow
(m)
31-Jul-10
14
2-Aug-10
18
7-Aug-10
22
8-Aug-10
14
11-Aug-10
11
13-Aug-10
21
15-Aug-10
12
22-Aug-10
46
23-Aug-10
55
25-Aug-10
40
27-Aug-10
13
29-Aug-10
45
31-Aug-10
43
1-Sep-10
40
7-Sep-10
13
8-Sep-10
15
9-Sep-10
17
15-Sep-10
19
16-Sep-10
19
22-Sep-10
16
mean
contributing area= 9.36 ha
weir dimensions
height
width
crosssectional
area
0.43
0.21
0.05
0.08
0.35
0.06
0.43
0.41
0.15
0.05
0.43
0.03
0.04
0.05
0.36
0.35
0.05
0.16
0.41
0.31
Velocit
y (d/t)
m/s
Flo
w
area
0.7
0.6
0.4
0.7
0.9
0.5
0.8
0.2
0.2
0.3
0.8
0.2
0.2
0.3
0.8
0.7
0.6
0.5
0.5
0.6
0.5
0.2
0.1
0.1
0.4
0.1
0.5
0.5
0.2
0.1
0.5
0.0
0.0
0.1
0.4
0.4
0.1
0.2
0.5
0.4
0.45
1.17
0.53
39
Discharg
e
Discharg
(Q=A.V) e Qm3/hr
m3/s
0.35
0.14
0.03
0.06
0.36
0.03
0.41
0.10
0.03
0.01
0.40
0.01
0.01
0.02
0.33
0.28
0.03
0.10
0.25
0.22
1264
493
94
231
1313
122
1469
373
117
53
1430
31
39
56
1197
996
116
362
909
799
Q
m3/hr/h
a
135.0
52.6
10.1
24.6
140.3
13.1
156.9
39.8
12.5
5.6
152.8
3.3
4.2
6.0
127.9
106.4
12.4
38.7
97.1
85.4
57.4
Appendix 4: Surface Runoff Discharge in the Treated Area (measured under
weir_2)
Date
2-Aug-10
7-Aug-10
8-Aug-10
11-Aug-10
13-Aug-10
15-Aug-10
22-Aug-10
23-Aug-10
25-Aug-10
27-Aug-10
29-Aug-10
31-Aug-10
1-Sep-10
7-Sep-10
8-Sep.10
9-Sep-10
15-Sep-10
16-Sep-10
22-Sep-10
mean
Time
taken by
the
floater
seconds
(s)
33.33
43.48
19.00
13.33
55.56
14.08
76.92
76.92
43.00
15.00
44.00
42.00
37.00
13.00
14.00
21.74
43.48
15.00
14.00
depth
of
flow
m
velocit
y (d/t)
m/s
0.36
0.25
0.23
0.38
0.20
0.45
0.26
0.29
0.05
0.37
0.05
0.06
0.04
0.35
0.43
0.35
0.32
0.36
0.40
0.3
0.2
0.5
0.9
0.2
0.9
0.1
0.1
0.2
0.7
0.2
0.2
0.3
0.8
0.8
0.5
0.2
0.9
0.9
flow
are Discharge
a
(Q = AV)
(A)
m3/s
2
m
0.2
0.1
0.1
0.2
0.1
0.2
0.1
0.1
0.0
0.2
0.0
0.0
0.0
0.1
0.2
0.1
0.1
0.2
0.2
contributing area= 5.03 ha
weir dimensions
height
0.4
width
1.06
cross0.42
sectional
area
40
0.05
0.02
0.05
0.15
0.02
0.17
0.01
0.02
0.00
0.10
0.00
0.01
0.00
0.11
0.15
0.07
0.03
0.17
0.15
Q
m3/h
r
Q
m3/hr/ha
165
88
185
522
55
618
52
58
18
377
17
22
17
411
525
267
112
626
531
246
32.8
17.4
36.7
103.8
10.9
122.9
10.3
11.4
3.5
74.9
3.4
4.3
3.3
81.7
104.4
53.1
22.3
124.5
105.6
48.8
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
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
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
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
P14
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
3.77
Elev of
bottom
piezom
Elev.
of avg
water
table
2575
3.19
2575
1.88
2580
3.6
2580
3.55
2589
3.4
2589
1.89
2610
3.57
2610
2.91
2617
2.72
2617
1.79
2611
1.5
2611
1.38
2600
1.59
2600
1.38
2585
2.31
2585
1.69
2573
2
2573
2.88
2565
2.28
2565
2.08
2535
3.12
2535
2.67
2520
1.78
2520
2.4
2571
2.6
2572
2.41
2578
0.87
2578
P14
2562
P13
2563
P12
2554
P11
2555
P10
2555
P9
2555
P8
2549
P7
2551
P6
2545
P5
2546
P4
2540
P3
2542
P28
2550
P27
2551
P26
2565
P25
2566
P24
2540
P23
2541
P22
2553
P21
2554
P17
2536
P15
2538
P18
2532
P16
2533
P20
2513
P19
2514
P2
2510
P1
Avg
depth
of
water
table
from
surface
2512
date
47
47
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.
2.
3.
4.
5.
6.
7.
What are the major crops you have been using to your farmland? ---------------------------------------------------------------------------------------------------------------------Is there a major change in cropping pattern during the last 15 years? If yes what
are the reasons?
------------------------------------------------------------------------------------------------------------------------------------------------------How does change in cropping pattern affect soil erosion? ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Do you have a problem of erosion in your farm?
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------How do you know soil erosion occurs on your farm land? (Indicators)---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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 ------------------------------------------------------------------------------------------------------------------------From where dose the major runoff that cause soil erosion in your farm come
from?
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
48
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?
49
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?
50