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Identification of potential rain water harvesting areas in the Central
Rift Valley of Ethiopia using a GIS�based approach
Master of Science Minor Thesis
Girma Moges Ketsela
August, 2009
Girma Moges Ketsela
MSc Minor Thesis
Identification of potential rain water harvesting areas in the
Central Rift Valley of Ethiopia using a GIS�based approach
Master of Science Minor Thesis
Name : Girma Moges Ketsela Registration No. : 771224430080 Program : Agricultural and Bioresource Engineering Course code : Number of Credits : 24 ects Examiner : prof. dr ir PWG Groot Koerkamp Supervisor : Willem Hoogmoed, Herco Jansen and Huib Hengsdijk Chair Group : Farm Technology Bornsesteeg 59 6708 PA Wageningen P: 03176482980
F: 03176484819
Dedication
To my wife, Nitsuh Girma (Baricho) to her love and dedication
i
ACKNOWLEDGEMENT
Firstly, I am sincerely grateful to the Netherlands Fellowship Program
(NFP/NUFFIC) for their financial support in the form of a scholarship to
undertake this MSc study in The Netherlands. Secondly, I like to thank the
project ‘Improving livelihoods and resource management in the Central Rift
Valley of Ethiopia (ILCE)’ of the partnership program of the Dutch Ministry
of Foreign Affairs – Development Cooperation and Wageningen University
and research centre on Globalization and sustainable rural development within
theme 2 -- Competing claims on natural resources, for funding this MSc work.
I would like to thank my supervisors, Dr. Willem Hoogmoed, Ir. Herco Jansen
and Dr. Huib Hengsdijk for the guidance, constructive comments throughout
this work and for the supervision during fieldwork.
I am thankful to the staff of Melkassa Agricultural Research Center for
providing me the necessary material. My very special thanks go to Tewodros
Mesfin for the logistic support, Yusuf Kedir for allowing me to use his
literature collected for years and Mezgebu Getnet for sharing data. I would
like to thank three of you for the scientific discussions.
A lot of thanks to my friends: Akililu Alem, Minwiyelet Nigatu, Urulo
Kebede, Birtukan Kebede, Getahun Tolla and Yonas Berhane for the
enjoyable time spent together.
I would like to extend my heartfelt thanks and love to my parents, my father
Moges, my mother Sintayehu, my brother Alemayehu (Chuchu) and my
sisters Bezawit, Selamawit and Rediet. Their continuous encouragement to be
successful from my early childhood has given me the energy to overcome the
difficulties I faced.
Last but not least, great thanks and love to my wife, Nitsuh Girma (Baricho)
for her care and affection in particular and for her love and endurance at large.
I would also like to thank her for being patient when I was busy with my
work.
ii
TABLE OF CONTENTS
Acknowledgement ......................................................................................................... i
Table of Contents.......................................................................................................... ii
List of Figures .............................................................................................................. iv
List of Tables .................................................................................................................v
List of Abbreviations and Acronyms........................................................................... vi
1. Introduction................................................................................................................9
1.1 Background ..........................................................................................................9
1.2 Problem statement..............................................................................................11
1.3 Objectives ..........................................................................................................13
1.4 Outline of the report...........................................................................................14
2. Literature review......................................................................................................15
2.1 RWH definition and classification.....................................................................15
2.2 History of RWH in Ethiopia ..............................................................................18
2.3 RWH in Ethiopia................................................................................................19
2.4 Evaluation of RWH in Ethiopia.........................................................................21
2.5 Experiences of other countries...........................................................................24
2.6 Critical factors for RWH site selection..............................................................27
3. Material and methods...............................................................................................30
3.1 Study area...........................................................................................................30
3.2 Identifying and assessing existing RWH structures...........................................31
3.3 Methodology of RWH potential mapping .........................................................32
3.3.1 General approach ........................................................................................32
3.3.2 Criteria selection and assessment of suitability level .................................32
3.3.3 Establishing the criteria weights .................................................................37
3.3.4 GIS Database ..............................................................................................40
3.3.5 GIS Analysis ...............................................................................................43
3.3.6 Evaluation ...................................................................................................44
4. Results and Discussions...........................................................................................46
4.1 Survey results.....................................................................................................46
4.1.1 RWH practiced............................................................................................46
4.1.2 Current state of affairs ................................................................................47
4.1.3 Use of harvested water................................................................................48
iii
4.1.4 Productive purpose of RWH.......................................................................49
4.1.5 Operation and maintenance.........................................................................50
4.1.6 The best option?..........................................................................................51
4.1.7 Lifting mechanism ......................................................................................53
4.1.8 Farmers’ involvement during implementation............................................53
4.1.9 Community ponds.......................................................................................54
4.2 Identification of potential RWH areas in the CRV............................................55
4.3 Validation...........................................................................................................62
5. Conclusions and recomendations.............................................................................64
References....................................................................................................................66
Appendices...................................................................................................................70
iv
LIST OF FIGURES
Figure 1: Classification of water harvesting techniques ...................................... 18
Figure 2: The Continuous Rating Scale developed by Saaty (1977). ................... 38
Figure 3: Textural map.......................................................................................... 42
Figure 4: Soil depth map....................................................................................... 42
Figure 5: Rainfall surplus map.............................................................................. 42
Figure 6: Slope map .............................................................................................. 42
Figure 7: Groundwater depth map ....................................................................... 43
Figure 8: Land cover map..................................................................................... 43
Figure 9: Flow chart for identification of potential sites. ..................................... 44
Figure 10: ponds lined by combining cement, sand and ‘kuyissa’ ....................... 48
Figure 11: The corrugated sheet were stolen ........................................................ 50
Figure 12 the owner used the corrugated sheet for other purposes and left the
tank open................................................................................................ 50
Figure 13: this pond was left unprotected and livestock was drinking directly
from the pond.........................................................................................51
Figure 14: pond at Edo kejele kebele with no water............................................. 53
Figure 15: RWH used for raising pepper seedling at Bulbula Wereda, Aleaku
Gubantaboke kebele............................................................................... 53
Figure 16: Percent of the study area per each suitability level for pond............... 56
Figure 17: Percent of the study area per each suitability level for in-situ ............ 56
Figure 18: Distribution of pond suitability level per land cover type................... 59
Figure 19: Distribution of in-situ suitability level per land cover type................. 59
Figure 20: Percent of very high and high suitability per Woreda area. ................ 60
Figure 21: Percent of very high to high suitability for each Woreda per total
very high and high suitability area......................................................... 61
Figure 22: Pond suitability map............................................................................ 62
Figure 23: In-situ suitability map.......................................................................... 62
Figure 24: In-situ suitability map with criteria given equal weights .................... 62
v
LIST OF TABLES
Table 1: Suitability rank for soil texture ............................................................34
Table 2: Suitability rank for soil depth ..............................................................35
Table 3: Suitability rank for rainfall surplus...................................................... 36
Table 4: Suitability rank for slope ..................................................................... 36
Table 5: Suitability rank for groundwater depth................................................ 37
Table 6: Suitability rank for land cover ............................................................. 37
Table 7: Pair-wise comparison matrix for ponds............................................... 39
Table 8: Pair-wise comparison matrix for in-situ.............................................. 39
Table 9: Weight (Percent of Influence). ............................................................ 39
Table 10: Very high and high suitability level per Woreda............................... 60
vi
LIST OF ABBREVIATIONS AND ACRONYMS
ADLI Agricultural Development-Led Industrialization
AHP Analytical Hierarchy Process
asl. above sea level
CA Catchment Area
CBO Community-Based Organizations
CRV Central Rift Valley
DEM Digital Elevation Model
ETB Ethiopia birr (currency 1birr = 0.08 USD (August, 2009))
FAO Food and Agricultural Organization
FDRE Federal Democratic Republic of Ethiopia
GPS Global Positioning System
GIS Geographic Information System
HGL Halcrow Group Limited
GIRD Generation Integrated Rural Development
HH Household
Kebele smallest administrative unit in the Ethiopian government structure
MCE Multi Criteria Evaluation
MoARD Ministry of Agricultural Rural Development
NGO Non Governmental Organization
OIDA Oromia Irrigation Development Authority
RWH Rainwater Harvesting
SNNPR Southern Nations Nationalities and Peoples Region
WLC Weighted Linear Combination
WOP Weighted Overlay Process
Woreda Administrative boundary comprising various Kebeles
vii
ABSTRACT
The Central Rift Valley (CRV) in Ethiopia is characterized by erratic rainfall
and high evapotranspiration. Total annual rainfall is sufficient for crop
production but the highly variable distribution in time and space frequently
threatens crop production and contributes to food insecurity. Rainwater
harvesting (RWH) for supplementary irrigation has been proposed in the
literature to mitigate dry spells. During the last decade, the Ethiopian
Government and various civil society organizations have supported the
implementation of RWH interventions throughout the country, including the
CRV. A systematic identification of areas suitable for different forms of RWH
may contribute to more effective interventions and targeted investments in
RWH.
The objective of this study is to identify potential suitable areas for RWH in
the CRV using Geographic Information Systems (GIS). In addition, a survey
has been conducted in selected Woredas of the CRV to identify and evaluate
qualitatively recent RWH interventions, and to support the prioritization of
suitability criteria and the validation of the developed suitability maps. A GIS-
based model has been developed to generate suitability maps for ponds and
in-situ RWH by using multi criteria evaluation. Six suitability criteria were
identified, i.e. soil, climate, topography, land cover, climate and groundwater
depth for RWH ponds while for in-situ RWH the same criteria were used
except groundwater depth. For each criterion five suitability levels were
identified, i.e. ‘very high’, ‘high’, ‘moderate’, ‘low’ and ‘very low’. Weights
were assigned to the criteria based on their relative importance for RWH
using an analytical hierarchical process. Using ArcGIS, maps for each
criterion were prepared and suitability maps for RWH ponds and in-situ
RWH.
The field survey showed that the majority of the RWH interventions in the
CRV consist of household ponds and tanks, and community ponds of which the
majority is not functioning satisfactorily. Reasons for the poor performance
are manifold but in general relate to improper site selection and RWH design
viii
and to the lack of ownership. The suitability maps show that the area with a
very high and high suitability for RWH ponds is about 4994 km2, which is
about 49% of the total study area; For in-situ RWH this area is about 6145
km2, or 60% of the total study area. The suitability maps provide an easy to
understand source of information to quickly identify areas that are more
promising than other areas for RWH intervention. The applied method can be
modified easily to incorporate other criteria or information with other spatial
resolution. It is concluded that suitability mapping using GIS is a flexible,
time-efficient and cost-effective method to screen large areas for RWH-
suitability facilitating decision-making for investments in RWH.
Keywords: Rainwater harvesting, GIS, Central Rift Valley, Ethiopia
9
1. INTRODUCTION
1.1 Background
Ethiopia is located in the Horn of Africa with an estimated population of
approximately 80 million. Agriculture is the mainstay of the Ethiopian economy
providing 60% of the Gross Domestic Product. It generates about 88% export
earnings and provides the majority of the employment. Many of the Ethiopian
smallholders depending on rainfed agriculture are food insecure. In many places, the
amount of rainfall and the duration of the rainy season are highly variable frequently
resulting in low crop yields and associated low incomes.
Surprisingly, Ethiopia is well-endowed with water resources (Sileshi et al. 2003). The
total annual runoff is estimated at 110 billion m3 however, much of which are carried
away by trans-boundary rivers. Groundwater reserves are estimated at 2.6 billion m3.
These natural resource bases have a potential for supporting a far greater number of
people than the current population (Seyoum 2003). However, current use of the
available water resources is very limited. For example, only 0.2 million ha is currently
irrigated (Alem 1999) which is less than 5% of the total land suitable for irrigation
(Dubale 2003). Large-scale dam and irrigation projects have not been widely
implemented in Ethiopia as they have often proved to be too expensive and
demanding in terms of construction and maintenance (Rämi 2003). Moreover, the
country is unable to utilize its large rivers for irrigation development due to various
reasons (Desta 2004). Therefore, rainfed agriculture is still the backbone of the
country’s economy and rural livelihoods.
Rainfed agriculture in semi-arid areas of Ethiopia is suffering from moisture stress
(Temesgen 2007), which is a major limiting factor for successful crop production.
The Central Rift Valley (CRV), 150 km southeast of Addis Ababa, is one of those
environmentally vulnerable areas in Ethiopia where poverty and natural resource
degradation are intertwined. The predominant livelihood strategy for the majority of
10
the population in the CRV (about 1.5 million) is the small mixed rainfed farming
system comprising cereal and livestock production. Because of large differences in
rainfall distribution between years and within years coupled with short rainy seasons,
rainfed agriculture is very susceptible to water shortage (Jansen 2009). The average
annual rainfall recorded in most of meteorological stations in the CRV is well above
700 mm yr-1 (Jansen et al (2009). In theory, this amount would be sufficient to grow
crops, yet large areas do not achieve food self-sufficiency. The underlying reason for
low crop yields might be that a high proportion of the rainfall is not available to the
crops because of excessive surface runoff and unproductive soil evaporation. Hence
the water availability to crops can be improved if the rainwater is retained in the area.
Improving the performance of rainfed agriculture is key to improve the livelihoods of
rural poor people. Rainwater harvesting (RWH) can improve agricultural production
by making water available during the time of dry spells. RWH is the deliberate
collection of rainwater from a surface known as catchment and its storage in physical
structures or within the soil profile (Mati et al. 2006). A small pond (~1000 m3) filled
by runoff can provide about half the water requirements of a half hectare plot to
overcome a mid season dry spell (Senay and Verdin 2004).
Rainwater harvesting can be practiced to provide water for irrigation, domestic water
and water for livestock. It can also serve as a way to replenish groundwater. The
rainwater harvesting techniques most commonly practiced in Ethiopia are runoff
irrigation (run-off farming), flood spreading (spate irrigation), in-situ water harvesting
(ridges, micro basins, etc.) and roof water harvesting (Alem 1999). Traditionally,
ponds are the main RWH structures in the Ethiopian Rift Valley where groundwater is
deep and other sources of water are not available (Alem 1999). Mostly, water
collected in ponds is used for growing vegetables and fruits around homesteads for
markets and home consumption.
Rainwater harvesting and storage has been recognized by the Ethiopian government
as a promising way for improving the water availability for crop production, domestic
11
use and water for livestock. To mitigate the erratic nature of rainfall in the arid and
semi-arid parts of the country, a national food security strategy based on the
development and implementation of rainwater harvesting technologies either at a
village or household level was adopted (Amha 2006). Accordingly, the Federal
Government allocated a budget for food security programs, ETB 100 million and
1,000 million ETB1 for 2002 and 2003, respectively. The majority of the budget was
used by regional states for the construction of RWH schemes including household
ponds (Rämi 2003).
1.2 Problem statement
Crop production in Ethiopia is mainly practiced under rainfed conditions and this
sector is the back bone of the country’s economy. Major part of this crop production
is in semi-arid areas such as in the CRV. To increase crop yields and improve food
security, effective planning and development of water resources in the CRV is
critically important.
Over the years, the Ethiopian government together with non-governmental
organizations has been involved in the development of RWH to enhance water
availability for crop production, drinking water for humans and livestock. The
government identified 315 very highly to moderately vulnerable Woredas (districts)
according to a number of criteria that includes drought risk, probability of extreme
weather conditions and past emergency needs (Profile 2005) and excavated many
ponds since 2003 mainly in four regions (Amhara, Tigiray, Oromia, SNNPR).
Although governmental and non-governmental organizations have been advocating
the use of RWH to improve the livelihoods of rural people, the implementation has
been confined with a range of problems and its adoption is low. A number of studies
(Alamerew 2006; Chala et al. 2004; Chala et al. 2003; Rämi 2003) suggested that
1 ETB= Ethiopian birr, 1birr=0.08 USD (August, 2009)
12
most of the constructed RWH are not performing as anticipated in terms of harvesting
and storing adequate amounts of runoff to meet the water demands particularly for
crop production due to various reasons.
One of the reasons is that there is the lack of scientific information to properly
allocate and plan RWH interventions. Currently, most RWH interventions are planned
on ad-hoc basis without much knowledge about the location-specific conditions. A
more systematic approach to the selection of feasible sites for RWH interventions
may improve their performance and rate of adoption.
The selection of potential areas depends on a multitude of factors including
biophysical and socio-economic conditions. Different studies used different
parameters. For instance FAO (2003) as cited by Kahinda et al. (2008) lists six key
factors to be considered when identifying RWH sites: climate (rainfall), hydrology
(rainfall–runoff relationship and intermittent water courses), topography (slope),
agronomy (crop characteristics), soils (texture, structure and depth) and socio-
economic criteria (population density, work force, people’s priority, experience with
RWH, land tenure, water laws, accessibility and related costs). Rao et al. (2003)
identified land use, soil, slope, runoff potential, proximity, geology, and drainage as a
criteria to identify suitable sites for RWH. Kahinda et al. (2008) used physical (land
use, rainfall, soil texture and soil depth), ecological (ecological importance and
sensitivity category) and socio-economic factors.
Ground survey is the best technique to identify suitable areas for RWH in relatively
small areas as it gives detailed information and does not need any interpolation
between points resulting in less variation from the actual nearby estimate. However
for larger areas like the CRV, ground survey is difficult and time consuming. The
application of GIS can be helpful for a first screening and identification of areas
potentially suitable for RWH (Prinz et al. 1998). However, the application of GIS for
identification of RWH potential areas in Ethiopia is almost not existing and there is
no documented work in this regard. GIS is a powerful set of tools used to collect,
13
store, retrieve, transform and display spatial data from the real world for a particular
purpose (Burrough 1986). GIS has been recommended as a decision-making and
problem-solving tool in RWH during the decision-making process (Mbilinyi et al.
2005). The purpose of this investigation is to identify potential areas suitable for
RWH in the CRV. For this purpose the combined effort of GIS analysis and field
surveys is used. The data from field surveys on current RWH interventions in the
CRV provide and supplement information to fine tune and calibrate the used GIS-
based methodology.
1.3 Objectives
• To identify and evaluate qualitatively selected existing rainwater harvesting
interventions in the CRV.
• To identify potential areas for different types of rainwater harvesting in the
entire CRV
14
1.4 Outline of the report
This report is structured in five sections. In section 1, a general introduction of the
study area was given and the problem of water shortage in Ethiopia particularly in
CRV is addressed. The need for more understanding of RWH to mitigate dry spells
along with the importance of using GIS in identifying potential areas is also
presented.
In section 2, a literature review on RWH is presented along with the general
classification of RWH interventions including a historical background of RWH in
Ethiopia.
In section 3, starting with the description of the biophysical characteristics of the
CRV, the data collection and research methodology are presented.
In Section 4, the results are presented and discussed. First, the result from field survey
in section 4.1 and the result from the GIS analysis for the identification of potential
areas in the sections 4.2 and 4.3.
Section 5 summarizes the overall conclusions based on the results followed by
recommendations for further studies.
15
2. LITERATURE REVIEW
2.1 RWH definition and classification
As water harvesting is an ancient tradition and has been used for millennia in most
drylands of the world, many different techniques have been developed. However, the
same techniques sometimes have different names in different regions and others have
similar names but, in practice, are completely different (Oweis 2004). Consequently,
there are a dozen of different definitions and classifications of water harvesting
techniques and the terminology used at the regional and international levels has not
yet been standardized (Nasr 1999).
Kahinda et al. (2008) defined RWH as the collection, storage and use of rainwater for
small-scale productive purposes. Critchley (1991) defined it as the collection of
runoff for productive use. Oweis (2004) defined it as the concentration of rainwater
through runoff into smaller target areas for beneficial use. Mati et al. (2006) defined
RWH as the deliberate collection of rainwater from a surface known as catchment and
its storage in physical structures or within the soil profile.
Runoff may be harvested from roofs and ground surfaces as well as from intermittent
or ephemeral watercourses and thus water harvesting falls into two broad categories:
Water harvesting techniques which harvest runoff from roofs or ground surfaces
named RWH and all systems which collect discharges from water courses named
flood water harvesting (Critchley et al. 1991). RWH technologies and systems can be
classified in several ways, mostly based on the runoff generation process, size of the
catchment and type of storage. Runoff generation criteria yields two types of systems
i.e. runoff based systems (runoff concentrated from a catchment) and in-situ water
conservation (rainfall conserved where it falls). The runoff storage criteria yield two
categories, i.e., storage within the soil profile and storage structures. The size of
catchment yields two categories, i.e., macro catchments and micro catchments (within
field). A simplified and practical classification of the various water harvesting
16
techniques and their characteristics and uses which was established by the World
Bank within the context of the “sub- Saharan Water Harvesting Study” in 1986- 1989
is shown in Figure 1.
In general, RWH systems for crop production are divided into three different
categories basically determined by the distance between catchment area (CA) and
cropped basin (CB) (utilization area): In-situ RWH, internal (Micro) catchment RWH
and External (Macro) catchment RWH (Hatibu and Mahoo 1999). To give the general
overview of the three categories, a short summary extracted from Hatibu and Mahoo
(1999) for each is presented below.
A. In-situ RWH
The first step in any RWH system involves methods to increase the amount of water
stored in the soil profile by trapping or holding the rain where it falls. This may
involve small movements of rainwater as surface runoff in order to concentrate the
water where it is wanted most. In-situ RWH is sometimes called water conservation
and is basically the prevention of net runoff from a given cropped area by holding
rainwater and prolonging the time for infiltration. This system works better where the
soil water holding capacity is large enough and the rainfall is equal or more than the
crop water requirement. Essentially, it includes all conventional approaches to soil
and water conservation designed to enhance rainwater infiltration. Examples of in-situ
RWH techniques include deep tillage, dry seeding, mixed cropping, ridges and
borders, terraces (“fanya juu” and “fanya chini”) and trash lines (Mbilinyi et al.
2005), vegetative / stone contour barriers, contour trenching, contour farming and tie
ridging methods (Sivanappan 2006).
B. Internal (Micro) catchment RWH
This is a system where there is a distinct division of CA and CB but the areas are
adjacent to each other. This system is mainly used for growing medium water
17
demanding crops such as maize, sorghum, groundnuts and millet. The major
characteristics of the system include small semi-circular pits, strip catchment tillage,
contour bunds, semi-circular bunds, meskat-type system and land conservation
aspects.
C. External (Macro) catchment RWH
This is a system that involves the collection of runoff from large areas which are at an
appreciable distance from where it is being used. This method is sometimes applied
with intermediate storage of water outside the CB for later use as supplementary
irrigation.
This system involves harvesting of water from catchments ranging from 0.1 hectare to
thousands of hectares either located near the cropped basin or far away. The
catchment areas usually have slopes ranging from 5-50%, while the harvested water is
used on cropped areas which are either terraced or on flat lands. When the catchment
is large and located at a significant distance from the cropped area the runoff water is
conveyed through structures of diversion and distribution networks. The most
important systems included in this category area hillside sheet/rill runoff utilization,
floodwater harvesting within the stream bed and ephemeral stream diversion.
18
Figure 1: Classification of water harvesting techniques (FAO, Critchley et al.(1991))
2.2 History of RWH in Ethiopia
The history of RWH practices in northern Ethiopia dates back as early as 560 BC,
during the Axumite Kingdom. In those days, rainwater was harvested and stored in
ponds for agriculture and domestic use (Seyoum 2003). Other evidences include the
remains in one of the oldest castles in Gondar (Fasiludus) from the 17th century which
used to have a sophisticated RWH system with a flume used for transporting water to
the palace pool used for swimming and religious rituals. In the south of the country,
the Konso people have a long and well-established tradition of building terraces to
harvest rain water for producing sorghum under extremely harsh environmental
conditions, i.e., low, erratic and unreliable rainfall (Alem 1999).
Water Harvesting
Rainwater Harvesting
(Local source)
Floodwater Harvesting
(Channel flow)
Runoff Harvesting Rooftop harvesting
Soil storage Deep ponding
Water
supply
Deep ponding
Plant
production
Water
supply
Deep ponding Soil storage
Water
supply
Plant
production
Micro-catchment
systems
Runoff Farming Floodwater farming
External catchment
systems
Category of
WH by source
Storage
Productive
use
Main plant
production categories
Sub division
19
Despite its long history, only a few decades ago RWH has received renewed attention
from policy makers. According to Promotion and application of RWH techniques
addressing water scarcity began through the government-initiated soil and water
conservation programs as response to the 1971-1974 (during Derg regime) drought in
Tigray, Wollo and Hararge (Seyoum 2003). However, the intervention was limited
because of the low level of community participation and declining attention by the
government.
After the fall of the military Derrg regime, both the Transitional Government of
Ethiopia (TGE), established in 1991, and the Federal Democratic Republic of
Ethiopia (FDRE), established in 1995, adopted the Agricultural Development-Led
Industrialization (ADLI) strategy, which emphasises improvement in agricultural
productivity to achieve food security and sustainable development. Besides,
recognizing the problem of variability in the rainfall distribution across the country,
the strategy advocates water-centered sustainable rural development (Desta, 2004).
Based on this, many different RWH technologies have been developed by regional
states, NGOs, communities, and individual farmers throughout the country.
2.3 RWH in Ethiopia
Ethiopia comprises of three main agro-climatological zones, i.e., Wet, Dry and
Pastoral. The dry zone comprises about 68% of the total land, 45% of the total arable
land and over 25% of the population. Food security in these areas is tied to the small
farmers, who rely heavily on rainfed agriculture. In many places of this zone, the
amount of rainfall and the duration of the rainy season are variable resulting in low
crop yields and associated low incomes. These areas are often food insecure.
Water is considered as one of the three pillars (land, labour and water) for the
development in the Ethiopia’s Agricultural Development led Industrialization (ADLI)
policy and food security programs. The Ethiopian Government has committed
financial resources to increase the irrigated area (Soriano 2007). Rainwater harvesting
technologies at the village or household level are proposed by the government of
20
Ethiopia as a practical and effective alternative to improve the livelihoods of rural
people at little cost and with minimal outside inputs. The Ministry of Agricultural
Rural Development (MoARD) and respective regional Bureaus planned and
implemented aggressive and ambitious water harvesting programs along the country's
food security programs (Desta 2006).
The Ethiopia government, prior to the large-scale implementation of RWH
technologies, conducted a study/survey in most parts of the country and in some other
countries having a longer RWH experience. This resulted in a “water harvesting
technologies package” including household-based RWH systems providing water for
humans, livestock and home garden horticultural crops (Desta 2004).
The RWH techniques most commonly practiced in Ethiopia are run-off irrigation
(run-off farming), flood spreading (spate irrigation), in-situ water harvesting (ridges,
micro basins, etc.), roof water harvesting (Alem 1999), birkas2 in Somalia region and
different runoff basins in Konso (Amha 2006) shallow wells (Soriano 2007), Ellea
and Haffirs3 (Kedir 2009)
Like other regions, Oromiya regional state where most CRV located has started the
implementation of water harvesting technologies to overcome problems related to
food security and poverty. Based on this, several RWH technologies have been
constructed by the regional Government, NGOs, communities, and individual farmers
throughout the region within the last few years and more are planned. In 2002/2003,
83,400 ponds, 500 underground tanks and 6,100 hand dug wells were planned and
49% of the ponds, 102% of the underground tankers and 64% of the wells were
completed in the same year (Chala et al. 2003).
2 Birka a traditional way to harvest rainwater in Somalia region. 3 Ella - Traditional deep water well in Borena zone.
Haffirs – are earthen embankments constructed with the aid of heavy machinery.
21
Different types of in-situ RWH have been used in different parts of Ethiopia. In
Tigray, micro-basins (roughly 1 m long and < 50 cm deep) are often constructed
along retention ditches for tree planting. The major conservation structures, meant for
erosion control commonly practiced in Ethiopia also conserve water in-situ and
include soil bunds, stone bunds, fana yaju and grass strips Alem (1999). These are
constructed in contour or graded depending on the rainfall of the area. For high runoff
areas graded structures are used. In low rainfall areas of southern Ethiopia, farmers
have developed a highly specialized water harvesting system. The cropland is
prepared in multitudes of circular depressions (3-4 m in diameter and < 1 m deep)
where a variety of crops are inter-cropped (Rockström 2000). Tied ridging are
traditionally used by small farmers in the eastern Hrarghe area as in- situ RWH
technique in sweet potato system using hand hoe (EARO 2000).
2.4 Evaluation of RWH in Ethiopia
The implementation of thousands of RWH structure has been confined with a range of
problems. Most people working in the field of RWH argue that most of the
constructed RWH structures do not perform as planned. A number of studies have
been conducted to evaluate the performance of the ambitious plan of the government
to develop RWH. The studies were conducted by the government, NGOs or
Academia. Some studies assess financial benefit, some technical viability and others
focused on assessing past experiences and identifying ways forward in order to
facilitate Government policies.
According to the progressive evaluation report on the implementation of RWH in
Oromiya (Chala et al. 2003), 98% of sampled beneficiaries responded high seepage.
The amount of collected water was not sufficient to meet the intended purpose
according to 53% of the farmers in East Shoa and 22% in Welega. All the
beneficiaries indicated that the catchment for collecting runoff was sufficient but not
the size of the RWH structure. The report concluded that the status of the constructed
ponds was not good owing to various problems like the unavailability of plastic sheet
22
to reduce seepage losses, lack of coordination and facilitation during implementation,
while community and land holding size were not taken into account during the design
and implementation.
The evaluation of RWH ponds that were constructed in 2005 and 2006 in northern
Ethiopia, Tigray, showed that the large majority failed because of insufficient water
collection or leakage problems due to poor construction (Segers et al. 2007). In
addition, a considerable number of ponds suffered from lack of maintenance
contributing to the poor performance. Some RWH ponds were silted up completely
and remain as gentle depressions in the landscape. The other reason for failures was
that households did not construct or maintain the diversion channels and inlets that are
needed to harvest runoff water.
Similar conclusions were drawn by Alamerew (2006) who summarized the various
constraints in implementing the RWH projects including inadequate public awareness
and ownership of local communities, lack of adequate knowledge and skills in
management of RWH schemes, insufficient involvement of communities in planning
and implementation processes and lack of facilitation for establishment/strengthening
of community-based organizations (CBOs). In addition, the author pointed out that
the various RWH efforts lacked research, for example, on indigenous knowledge and
best practices in RWH, improving traditional practices and/or adapting new
technologies to local conditions which constitute among the critical inputs for a
successful intervention.
Field assessments by the Oromiya Irrigation Development Authority (OIDA)
identified problems with the implementation of RWH technology related to inefficient
runoff collection and unwise use of the harvested runoff (Chala et al. 2004). This is
due to poor catchment selection and characterization in relation to the structure design
and lack of information on the utilization of the system (like family drip irrigation).
The evaluation also collected opinions from non-target farmers (who don’t have
RWH), other OIDA staff and development agents (DAs) on to the issue “why RWH
23
structures don’t retain or hold water”. The answer from the three groups pointed at
high seepage losses attributed to either poor compaction, cracks in tanks, and poor site
selection due to a lack of experience.
A RWH impact assessment at Alaba Woreda showed a positive effect on agricultural
productivity (Amha 2006). The cropping pattern in the studied area changed and farm
households started to grow cash crops which were not previously grown in the area.
However, benefits depend on market and infrastructure access and crop
diversification to minimize risk. Despite its potential, adoption of RWH technology is
slow. Some reasons for the low adoption were poor quality of the construction
resulting in cracks in the cemented floor and loss of water, improper site selection
(insufficient runoff) and fear of malaria spread.
The RWH structures in Amhara and Tigray face many problems, many of which
originate from the speed and scale of implementation (Rämi 2003). Among the
identified problems were (1) poor site selection; it was done hurriedly and without
experience, with the consequence that many tanks do not hold water. Often the level
of poverty was used as the most important criteria for selection of target beneficiaries,
while the technical criteria of runoff and water collecting potential were neglected.
Poor site selection is the most important reason for failures. (2) Leakage; Most of the
tanks (cemented) were leaking due to cracks in the walls of the structures. This was
attributed to the lack of skilled labour during construction, the poor quality of work as
result of the quota system imposed by the regional Government that put junior experts
and development agents under pressure to construct tanks quickly. (3) siltation and (4)
wastage and uneconomical use of water.
In the semi-arid areas of Ethiopia, tied ridging as in-situ water harvesting have been
found to be very efficient in storing rain water particularly in drier seasons and lead to
substantial increase of yields in some of the major dry land crops including maize,
sorghum wheat and mung bean regardless the different planting patterns used, i.e.
24
planting in the furrow or on top of the ridge compared to the flat seed-bed (farmers
practice) (W/Giorgis 2002).
Promotion of RWH in Ethiopia has given more emphasis on structural storage (ex-situ
deep ponding) than in-situ RWH (Desta 2004). However, in-situ RWH is preferred as
it does not require water lifting from the pond and water application, is more closely
linked to traditions, and the costs are lower (Desta 2004). Ex-situ RWH is not suitable
for staple crops such as cereals, which are needed by the farmers to secure their food
needs as it is evaluated from cost benefit analysis. Mesfin (2004) also concluded that
the most efficient and cheapest way of conserving water is in-situ RWH. Evaporation
losses can be reduced greatly if rainfall is stored in the soil rather than in an open
structure. Gebre and Giorgis (1980) and Beyu and Alemu (1998) further concluded
that in-situ RWH practices are also more economically feasible to resource poor
farmers than ex-situ RWH methods.
Different studies in Ethiopia showed the potential of different in-situ RWH methods
to enhance soil moisture storage and rainfall use. Mesfin (2004) studied different in-
situ RWH methods on soil water storage and on the growth, grain yield and water use
efficiency of sorghum in the CRV and he concluded that soil moisture increased
compared to conventional tillage methods. Temsgen (2007) showed that tied-ridging
performed better in retaining water than the local tillage practice (with Maresha plow)
and inverted broad beds (with broad bed maker) providing more water to crop
production in a semi-arid region where rainfall is erratic.
2.5 Experiences of other countries
Water harvesting is an ancient technology practiced in many parts of world such as
North America, Middle East, North Africa, China, and India. Different indigenous
RWH techniques and systems have been developed and remain an important source
of water for agriculture in different parts of the world. The Middle-East and North-
Africa have a long tradition in RWH as one of the methods for survival in the area.
25
According to an assessment of desertification and RWH the first RWH system in
history was built in the Middle-East and North-Africa (Nasr 1999). Researchers have
found signs of early RWH structures constructed over 9000 years ago in the Edom
Mountains in southern Jordan. In Israel complete RWH systems have been found in
the Negev Desert, which were about 4000 years old.
Remnants of other RWH installations have also been discovered in Iraq and in the
Arabian Peninsula along the routes used by caravans. The RWH installations
consisted mainly of means to collect rainwater and divert it into natural and/or
artificial ponds and reservoirs. Other evidences of RWH have been found in Yemen,
Palestine, Morocco and Egypt. At present, all countries in the Middle-East and North-
Africa region practice intensively one or more RWH techniques to collect and store
rainwater for use in meeting crop, human and animal needs.
A study by Ngigia (2005) in the Laikipia district, Kenya showed that improved farm
ponds provide one of the feasible options of reducing the impacts of water deficit that
affect agricultural productivity in semi-arid environments in Sub-Saharan Africa. The
field evaluation revealed that on-farm RWH systems are common in the study area
with sizes ranging from 30 to 100 m3 and catchment areas varying from 0.3 to 2 ha.
The hydrological evaluation of the farm ponds revealed that one of the challenges was
how to reduce the seepage and evaporation water losses. He reported significant water
losses through seepage and evaporation, which accounted on average for 30–50% of
the stored runoff. The high losses are one of the factors that affect the adoption and
up-scaling of on-farm water storage systems. If seepage loss is reduced with lining
material and if RWH is combined with drip irrigation on-farm storage systems can be
economically viable and farmers are able to recover the full investment costs within 4
years
Another study in Kenya of the Mwala division on the impact of run-off water
harvesting for dry spell mitigation in maize showed that harvesting runoff water for
supplemental irrigation is a risk-averting strategy, pre-empting situations where crops
26
depend on rainfall that is highly variable both in distribution and amounts (Barron and
Okwach 2005 ). Water harvested and stored in an earthen dam provided a technically
feasible option to supplement crop water demand. By using underground spherical
tanks having a combined capacity of 60 m3, seasonal water for supplemental irrigation
for an area about 400 m2 was guaranteed. With RWH, farmers diversified production
through horticultural cash crops and dairy resulting in higher earnings compared to
those from rainfed maize. Barron and Okwach (2005) also showed that combining
supplemental irrigation and low N fertilizer inputs resulted in a yield increase of more
than 50%.
An evaluation study of small basin water harvesting in Jordan showed that a
‘Negarim’ micro-catchment of 25 m2 can provide enough water to support crop water
requirements if properly designed and if water holding capacity of the root zone is
adequate (Oweis and Taimeh 1996). Another study from Northern Burkina Faso
showed that RWH has potential for supplemental irrigation to ensure self sufficiency
of staple cereals for the small-holder farmer (Fox and Rockström 2000).
Fox et al. (2005) studied the risk associated with and economic viability of RWH for
supplemental irrigation in semi-arid Burkina Faso and Kenya and suggested that
supplementary irrigation can generate economic benefits and improve long-term food
self-sufficiency compared to rainfed agriculture. However, they stressed that the
investment in supplementary irrigation is economically viable, but only if it is
combined with growing a cash crop during the winter (dry) season.
Hatibu et al. (2004) tried to evaluate farmer-initiated and managed RWH systems on
farmers’ income and living standards using two districts in Tanzania, i.e. Maswa and
Same. They compared the performance of the RWH for maize in terms of yields,
gross margins and return to labor for the different levels of rainwater harvesting. The
levels of water availability were divided into four main categories: (1) rainfed system
where the farmer only captured and conserved the rainwater falling directly on the
field without additional water from external sources; (2) poor RWH in which the
27
farmers capture and conserve all direct rainfall (in-situ RWH) and also irregularly
obtain some extra run-off from external (micro-catchment) sources with reliability of
less than 25%; (3) medium RWH is where the reliability of obtaining runoff from
external (micro and macro-catchment) sources is above 25% but less than 75%; and
(4) a good RWH where the availability of runoff from external (macro-catchment)
sources was above 75% - and where storage ponds are used. Good RWH increases
yield of maize (in Same area) by four fold of rainfed yield level, and two fold for rice
(in Maswa area). They compared the performance of good RWH harvesting across
four different crops and they found that using rainwater harvesting for vegetable
production is consistently very beneficial to the farmer with returns to labor
exceeding US$ 10 per person day and in some years reaching nearly US$ 200 per
person day.
2.6 Critical factors for RWH site selection
Although the government and non-governmental organizations have been advocating
the use of RWH, its performance and adoption rate is not as much as it was
anticipated as different evaluation studies have shown and discussed above (section
2.4). It must be underscored, however, that the technology by itself is often not the
problem for the low performance and adoption, but rather the poor implementation.
Proper implementation including area selection and design could improve the
performance of RWH and improve the livelihoods of many poor.
The identification of potential areas suitable for RWH is therefore the key for a
successful RWH intervention. One of the main reasons for failure of RWH structures
is the lack of scientifically verified information which could be used to identify areas
where RWH can be applied and for which type of RWH techniques.
The potential of areas for RWH depends on a multitude of parameters, either physical
factors like rainfall, land use, soil and topography and/or the combination of the
physical factors and socio-economic factors.
28
FAO (2003) by Kahinda et al. (2008) lists six key factors to be considered when
identifying RWH sites: climate (rainfall), hydrology (rainfall–runoff relationship and
intermittent watercourses), topography (slope), agronomy (crop characteristics), soils
(texture, structure and depth) and socio-economic (population density, work force,
people’s priority, experience with RWH, land tenure, water laws, accessibility and
related costs). Rao et al. (2003) use land use, soil, slope, runoff potential, proximity to
the utility points (like irrigation and drinking water supply schemes), geology, and
drainage as a criteria to identify suitable sites for RWH. To develop a GIS-based
RWH model (RSM) that combines a Multi-Criteria Evaluation (MCE) process,
Kahinda et al. (2008) used physical (land use, rainfall, soil texture and soil depth),
ecological (ecological importance and sensitivity category) and socio-economic
factors. Ramakrishnan et al. (2008) used slope, porosity and permeability, runoff
potential, stream order and catchment area as criteria to select suitable sites for
various RWH /recharging structures in the Kali watershed, Dahod district of Gujarat,
using remote sensing and GIS techniques.
United Nations Environment Programme (Mati et al. 2006) conducted a study to
determine if RWH technologies can be mapped at continental and country scales. The
project utilized a number of GIS data sets including rainfall, land use, land slope, and
population density to identify four major commonly adaptable RWH technologies:
roof top RWH, surface runoff collection from open surfaces into pans/ponds, flood
flow storages and sand/sub-surface dams and in-situ RWH.
Another study deepened the scholarly understanding of the role of indigenous
knowledge to identify potential sites for RWH in Tanzania (Mbilinyi et al. 2005).
This study concluded that farmers have a substantial amount of knowledge on RWH
systems and identification of potential sites for different RWH systems. Most of
indigenous knowledge (although it varies among locations) is based on biophysical
factors, including topography, soil type and distance from water sources.
29
For relatively small areas, the critical factors can be assessed by field surveys
However, for larger areas the application of GIS can be helpful for a first suitability
screening with less time, cost and labour.
30
3. MATERIAL AND METHODS
3.1 Study area
The CRV in Ethiopia (38°00’-39°30’ E and 7°00’-8°30’ N) covers about 1 million ha
and is part of the Great African Rift Valley. The study area is in the centre of the
Ethiopian Rift, 150 km southeast of the Addis Ababa (Figure 2). CRV encompasses
parts of Oromiya Regional State and Southern Nations Nationalities and Peoples’
Regional State (SNNPR). The total population of CRV is approximately 1.5 million
with an average population density of 1.5 p ha-1 (Jansen 2009). The CRV is a closed
river basin with elevations ranging from 1600 m asl. in valley floor to about 3000 m
to the east and west. Annual rainfall in CRV ranges from about 600 mm near the lakes
at the valley floor up to 1250 mm in the higher elevations near the borders of the
basin. About 70% of the rainfall precipitates in the short rainy season (July to
September). The soils in the western part of the CRV are mainly Cambisols and
Luvisols in the hills and foot slopes, and Vertisols in parts of the flat plains.
The CRV is a mixture of moderately to intensively cultivated land, open bush, open
woodland, lakes and forest. Rainfed agriculture (moderately and intensively
cultivated) dominates the land cover in the CRV with an estimated area of 742600 ha
(more than 70% of the total). This rainfed agriculture depends much on the water
availability which is highly variable in terms of temporal and spatial distribution.
Irrigated agriculture is now increasing in the CRV especially around Meki town using
shallow groundwater and Lake Ziway as a source of water; however it is still minor as
compared to rainfed agriculture.
31
Figure 2: Location of study area with Woreda boundary
3.2 Identifying and assessing existing RWH structures
An inventory of past and recent RWH interventions in the study area was conducted
through a review of the literature, interviews with key stakeholders and a field survey
of RWH farmers. During the field survey data were collected through observations
and interviews with farmers using a semi-structured questionnaire (Appendix I). The
field survey focused on the type of RWH practiced, farmers’ experiences and
constraints, duration of water storage, water uses and application methods. This
helped to understand the bottlenecks and successes of RWH interventions in the CRV.
The qualitative assessment of the problems associated with RWH interventions
helped to identify the type of RWH for which the suitability map(s) were developed.
In addition, the collected field data were used to generate information to fine tune and
calibrate the methodology and validate the derived suitability maps.
32
3.3 Methodology of RWH potential mapping
3.3.1 General approach
The objectives and associated technologies for runoff harvesting are highly location-
specific, and depend on physiographic, environmental, technical and socio-economic
conditions. Therefore appropriate technologies are developed for particular regions
and cannot simply be replicated in other areas (Winnaar et al. 2007).
The identification of suitable areas for RWH is a multi-objective and multi-criteria
problem. The field survey indicated that most RWH interventions in the CRV
focus(ed) on (i) surface runoff collection from open areas and storage in ground-based
structures (ponds) and (ii) in-situ RWH and storage in the soil profile for crop
production Therefore, the objective of this report is to map potential areas for both
RWH interventions, i.e. for ponds and in-situ RWH. Six and five suitability criteria
for ponds and in-situ respectively were identified. This multi-objective multi-criteria
methodology involved the following major steps: (i) Selection of criteria; (ii)
assessment of suitability level for criteria for ponds and in-situ RWH; (iii)
assignments of weights to these criteria; (iv) collection of spatial data for the criteria
including GPS survey to supplement and generating maps for each using GIS tools;
(v) developing a GIS-based suitability model which combines maps through MCE
process; and (vi) generate suitability maps.
3.3.2 Criteria selection and assessment of suitability level
From the literature review (section 2.6) and information obtained from field survey
supported by expert judgment, six criteria were selected for the identification of
potential areas for ponds, i.e. (soil texture, soil depth, rainfall surplus (precipitation-
evapotranspiration), topography, groundwater depth and land cover. For in-situ the
same criteria were considered except groundwater depth. The criteria used in the GIS
analysis are presented and discussed below.
33
Because of the different scales on which the criteria are measured, MCE requires that
the values contained in the criterion map are converted into comparable units.
Therefore, the criteria maps was re-classed into five comparable units i.e suitability
classes namely; 5 (very high suitability), 4 (high suitability), 3 (medium suitability), 2
(low suitability), and 1 (very low suitability). The suitability classes are then used as
base to generate the criteria maps (one for each criterion).
3.3.2.1 Soil texture
The suitability of a certain area either as catchment or as cropping area in RWH
depends strongly on its soils characteristics. Soils with high infiltration rates, such as
sandy soils, are not favorable for RWH structures. A challenge in design and
construction of on-farm water storage structures, such as farm ponds, is how to
minimize water losses (mainly due to seepage and evaporation) (Ngigia et al. 2005).
Therefore, runoff harvesting into unlined ponds depends on soil type especially to
avoid seepage problems (Mati et al. 2006). For in-situ RWH, the actual suitability
will depend on the capacity of the soil to retain as well as to deliver water to the root
zone. Both soil texture and depth determine the total soil water storage capacity,
which controls the amount of water that is available using in-situ RWH for crops
during the dry periods (Oweis 2004).
Farm ponds are suitable in areas with low soil permeability (Rao et al. 2003). Based
on the survey results and the literature review, almost all constructed ponds in the
study area have seepage problem. Therefore, finding suitable areas for ponds in this
study area should be able to focus in locating areas with good potential in retain the
harvested water. Clay soils have low permeability( high hydraulic resistance) and can
hold the harvested water, and therefore they are the best soils for water storage
(Mbilinyi et al. 2005).
Regarding in-situ RWH, soils with high water holding capacity are suitable for ridges
and borders (in-situ) where as sandy soils are not suitable (Mbilinyi et al. 2005).
34
Therefore loamy soils are most suitable for in-situ RWH whereas clay soils are less
suitable because of their low infiltration capacity and risk of water logging.
Table 1: Suitability rank for soil texture
No. Soil textural class Pond Suitability In-situ Suitability
1 fine 5 2
2 Fine and medium 4 3
3 Medium 3 5
3 Medium and coarse 2 4
4 coarse 1 2
3.3.2.2 Soil depth
Soils should be deep enough to allow excavation to the prescribed depth for farm
ponds. One of the reason for the poor performance of RWH in Tigray was that the
prescribed pond depth had not been reached during construction (Segers et al. 2007).
According to another study (Rämi 2003), one farmer in Warkaja Kebele, Wollo was
advised to dig out a dome shaped underground-structure in order to collect roof water.
At a depth of three meters he found groundwater and was forced to stop digging.
Therefore, soil depth is considered as one of the criteria for pond suitability in this
study.
Soil depth is also important for identifying potential areas for in-situ RWH (for crop
production) as it ensures adequate rooting development and storage of the harvested
water. Critchley et al. (1991) consider soil depth as one criteria and suggest deeper
soil depth as suitable for various micro RWH methods. Kahinda et al.(2008) also use
soil depth as one criterion for selecting potential areas for in-field RWH.
35
Table 2: Suitability rank for soil depth
No. Soil depth class Depth(m) Pond In-situ
1 Very deep >1.5 5 5
2 Deep 1.0 - 1.5 2 5
3 Moderately deep 0.50 - 1.0 1 5
4 shallow 0.25 - 0.5 1 3
5 Very shallow <0.25 1 1
3.3.2.3 Rainfall surplus
The magnitude of harvestable rainfall plays a significant role in assessing the
suitability of RWH for a given area (Kahinda et al. 2008). Because of the very high
variability in distribution and amount of rainfall in the study area, it is very important
to consider the rainfall erraticness/ distribution, evapotranspiration and availability of
harvestable runoff. RWH is particularly relevant if rainfall is irregular than if rainfall
is evenly distributed over the year (Jansen 2009). The rainfall surplus is therefore
considered as criteria to account for the spatial distribution of harvestable runoff
availability. The logic behind calculating rainfall surplus relies on assumptions that the value of
difference between rainfall and evapotranspiration indicates runoff availability.
The rainfall surplus is calculated by subtracting long-term average monthly values of
the evapotranspiration from the precipitation (P-ET) for seven meteorological
stations. The annual rainfall surplus was calculated at each metrological station by
adding only the positive values of the difference (P-ET). Then the spatial distribution
of the rainfall surplus was generated by interpolating the point values. High suitability
rank was given for areas with large rainfall surplus as it ensures the availability of
runoff to be harvested.
36
Table 3: Suitability rank for rainfall surplus
No. Rainfall surplus class Values(mm) Pond In-situ
1 Very large deficit < 75 1 1
2 Large deficit 75 - 150 2 2
3 Medium deficit 150 - 225 3 3
4 Small surplus 225 – 300 4 4
5 Large surplus > 300 5 5
3.3.2.4 Topography
The slope of land is important in site selection and implementation of all ground
based RWH systems, especially ponds, pans, weirs and also in-situ RWH (Mati et al.
2006). In-situ RWH is not recommended for areas where slopes are greater than 5%
due to uneven distribution of run-off and large quantities of earthwork required which
is often costly (Critchley et al. 1991). Farm ponds are generally more appropriate in
areas having a rather flatter slope however a slight slope is needed for better
harvesting of the runoff. Therefore flat areas with a slope less than 2% were assigned
a higher suitability rank for in-situ RWH whereas for ponds areas with slope ranging
from 2 to 8% were given higher suitability rank.
Table 4: Suitability rank for slope
No. Slope class Slope (%) Pond In-situ
1 flat <2 3 5
2 undulating 2-8 5 4
3 rolling 8-15 4 3
4 Hilly 15 – 30 2 2
5 mountainous >30 1 1
3.3.2.5 Groundwater depth
Ponds only make sense if any other alternative is not available. Investment into other
schemes (if any) like river diversion, hand dug and deep wells are generally favored
37
(Rämi 2003). Therefore, the depth of the groundwater layer was used as criterion for
the suitability of ponds; i.e. less weight was given to areas with groundwater
potential.
Table 5: Suitability rank for groundwater depth
No. Groundwater class Pond
1 <40m 2
2 40-120m 4
3 high relief area 5
3.3.2.6 Land cover
As this study focused on RWH for crop production, both in-situ and ponds should be
located close to agricultural areas. Therefore, the land cover was used as one criterion
for in-situ and pond RWH to identify potential areas on agricultural land.
Table 6: Suitability rank for land cover
No. Land cover class Land cover types Pond In-situ
1 Very high Intensively cultivated 5 5
2 high Moderately cultivated 5 5
3 medium Forest, exposed surface 2 1
4 Low/ restricted mountain 2 1
5 Very low/restricted Water body, urban area restricted restricted
3.3.3 Establishing the criteria weights
Since not all the criteria are equally important for the identification of potential RWH
areas, different weights were assigned to the criteria. For the development of weights,
the pair-wise comparison known as the Analytical Hierarchy Process (AHP)
developed by Saaty (1977) was used. Pair-wise comparison concerns the relative
importance of two criteria involved in determining the suitability for a given
objective. The rating between two criteria is provided on a 9-point continuous scale
(Figure 2) ranging from extremely less important to extremely more important. The
38
comparison is done for every possible pairing of criteria and the rating is entered into
a pair-wise comparison matrix. Only the lower triangular half of the matrix needs to
be filled in as the matrix is symmetrical.
1/9 1/7 1/5 1/3 1 3 5 7 9
extremely
very
strongly
strong ly
modera tely
equa lly
m odera tely
strong ly
very
strong ly
extremely
Less important More important
Figure 2: The Continuous Rating Scale developed by Saaty (1977).
During pair-wise comparison, criteria were rated based on the literature review, information from the field survey and discussions with people working and having experience with RWH. The relative weights for each criterion and suitability rank for classes are assigned for the two categories of RWH. The result from the pair-wise comparison is presented in The final weight calculation requires the computation of the principal eigenvector of
the pair-wise comparison matrix to produce a best-fit set of weights. For this
calculation the WEIGHT module of Idrisi software was used and the result is
summarized in Table 9. The Consistency Ratio (CR) of the matrix, which shows the
degree of consistency that has been achieved during comparing the criteria or the
probability that the matrix ratings were randomly generated, was 0.03 and 0.02 for
pond and in-situ, respectively, which is acceptable as the values are less than or equal
to 0.1 (Saaty 1977).
Table 7 and Table 8 for ponds and in-situ respectively.
39
The final weight calculation requires the computation of the principal eigenvector of
the pair-wise comparison matrix to produce a best-fit set of weights. For this
calculation the WEIGHT module of Idrisi software was used and the result is
summarized in Table 9. The Consistency Ratio (CR) of the matrix, which shows the
degree of consistency that has been achieved during comparing the criteria or the
probability that the matrix ratings were randomly generated, was 0.03 and 0.02 for
pond and in-situ, respectively, which is acceptable as the values are less than or equal
to 0.1 (Saaty 1977).
Table 7: Pair-wise comparison matrix for ponds.
Texture Depth Rainfall surplus Groundwater Land cover Slope
Texture 1 4 3 4 6 5
Depth 1/4 1 1 1 3 2
Rainfall surplus 1/3 1 1 3 4 3
Ground Water 1/4 1 1/3 1 3 2
Land cover 1/6 1/3 1/4 1/3 1 1/2
slope 1/5 1/2 1/3 1/2 2 1
Table 8: Pair-wise comparison matrix for in-situ.
Texture Depth Rainfall surplus Land cover Slope
Texture 1 2 3 7 4
Depth 1/2 1 2 5 3
Rainfall surplus 1/3 1/2 1 4 3
Land cover 1/7 1/5 1/4 1 1/2
Slope 1/4 1/3 1/3 2 1
Table 9: Weight (Percent of Influence).
Weights (%) No. Criteria Ponds In-situ
1 Soil texture 43.2 42.6
2 Soil depth 13.6 26.2
40
3 Rainfall surplus 19.8 17.8
4 Groundwater depth 11.5 Not used
5 Topography/slope 7.2 8.5
6 Land cover 4.6 4.9
Sum 100 100
3.3.4 GIS Database
The GIS dataset of the criteria required for the identification of suitable areas were
derived from available data sets most of them provided by Halcrow Group Limited
and Generation Integrated Rural Development (HGL and GIRD) Consultants, and
supplemented with information from a GPS survey. The GIS database required for
identifying RWH potential areas was developed using ArcGIS software, by utilizing
both vector and raster databases (Figure 3 - 8).
The soil textural map was derived from the land suitability dataset developed by HGL
and GIRD. This dataset has five textural classes namely coarse, medium and coarse,
medium, fine and medium and fine. The soil texture layer was clipped to the study
area and reclassified into five numerical categories and assigned different suitability
rankings for ponds and in-situ RWH. The suitability ranking is made on a scale from
1 to 5 with 5 implying most suitable (Table 1).
The soil depth layer was derived from the land suitability dataset of HGL and GIRD. This dataset has
five depth classes namely very deep (> 150 cm), deep (100-150 cm), moderately deep (75-100 cm),
shallow (50-75 cm) and very shallow (<50 cm). Then the soil depth layer was clipped to the study area
and reclassified to numeric values and assigned different suitability rankings for ponds and in-situ
RWH (
41
Table 2).
The rainfall surplus map was generated by interpolating seven rainfall surplus point
values. The values were calculated by subtracting evapotranspiration from
precipitation (P-ET) using data of seven meteorological stations in and near the study
area. The calculation was done for each month and for each station and the
accumulated rainfall surplus was calculated by adding the positive values of the
difference (P-ET) starting from rainy season. To get a surface map of rainfall surplus,
the calculated values were interpolated using the Inverse Distance Weight (IDW)
interpolation method of ArcGIS. The new data were clipped to the study area and re-
sampled to 90 m. The rainfall surplus map comprises five classes, i.e. large surplus,
small surplus, moderate surplus, small deficit and large deficit (Table 3).
A slope map, expressed in percentage, for the study area was derived from the DEM
(elevation dataset) with 90 m resolution obtained from HGL and GIRD. The slope
map was reclassified into five classes based on the FAO classification (FAO 2002 as
cited by Meti et. al.(2006)) namely 0-2% is flat; 2-8% is undulating; 8-16% is rolling;
16-30% is hilly; > 30% is mountainous and assigned different suitability rank for
ponds and in-situ RWH (Table 4).
The groundwater depth layer was generated by digitizing (on screen) the hydrological
map of the region which was obtained from the Ministry of Water Resource. The
dataset has three classes namely <40 m, 40-120 m and high relief area and these
values were converted into to numeric values (Table 5).
The land cover map was generated from landuse/cover (year 2006) dataset from HGL
and GIRD. The generated land cover map has 11 classes namely intensively
cultivated (52%), moderately cultivated (20%), water body (7.6%), shrubland (5.4%),
forest (4%), afro-alpine (4%), (1%), woodland (2%), marshland (1.6%), exposed
surface (1.4%) and urban area (0.1%). The land cover map was reclassified and
assigned numeric values (Table 6).
42
Figure 3: Textural map
Figure 4: Soil depth map
Figure 5: Rainfall surplus map
Figure 6: Slope map
43
Figure 7: Groundwater depth map
Figure 8: Land cover map
3.3.5 GIS Analysis
All the processing in finding RWH suitability map has been implemented in a suitability
model developed in the model builder of ArcGIS 9.3. The suitability model generates
suitability maps for RWH by integrating different input criteria maps using Weighted
Overlay Process (WOP) also known as Multi-Criteria Evaluation (MCE). MCE can be
achieved by a weighted linear combination (WLC) wherein continuous criteria (factors)
are standardized to a common numeric range, and then combined by means of a weighted
average. With a weighted linear combination, criteria are combined by applying a weight
to each followed by a summation of the results to yield a suitability map using the
following equation:
ii xwS ∑=
Where S = suitability wi = weight of factor i xi = criterion score of factor i
44
A number of tools of ArcGIS were incorporated in the model to solve various spatial
problems, i.e. calculating slope, reclassifying values, clipping, re-sampling, reprojecting,
over laying, etc. (Appendix II). All source maps were in vector type formats, each
containing their related attribute files. These have been converted into raster datasets and
then re-sampled to the same cell size (90 m) to enable the ArcGIS overlay operation. The
conceptual framework is shown in Figure 9.
3.3.6 Evaluation
Validation of the suitability maps was done by cross-checking the suitability map with
existing RWH structures. Global positioning system (GPS) readings were taken on
existing RWH structures and incorporated in the ArcGIS environment for analysis.
During the GPS survey, readings were taken from both successful and failed
interventions.
Figure 9: Flow chart for identification of potential sites.
45
46
4. RESULTS AND DISCUSSIONS
4.1 Survey results
The size of the survey on RWH structures is not large enough to represent all RWH
technology present in the study area. However, most RWH technologies in the area share
the same features, i.e design type, method of implementation, year of construction and
more or less similar social setup and results therefore point at some general success and
failure lessons. A total of randomly selected 30 households with different RWH
technologies were interviewed using a semi-structured questionnaire. Moreover, informal
group discussions were organized with farmers to discuss the various RWH interventions.
Additionally visual observations were made on existing RWH interventions to assess
their current status.
4.1.1 RWH practiced
The field study revealed that different types of RWH systems exist in the study area.
Many RWH systems at household level have been developed with support of the
Government, and especially ponds and concrete tanks can be found in almost every
Kebele. The household (HH) ponds have a trapezoidal shape and are 8-12 meters wide
and 2-3 meters deep. Tanks have a hemispherical shape with a capacity ranging from
approximately 40 m3 to 60 m3 and almost all surveyed tanks are cemented and roofed.
Most of the surveyed farmers with HH ponds and tanks have started to use the technology
since the year 2003/04 during which the government started extensive implementation of
RWH at HH level. None of the surveyed structures were built by farmers’ own capital but
mainly by government fund (MoRAD) and only few by NGOs. Farmers contributed
labour during the construction.
Community managed ponds are present in some Woredas. The community ponds in
Adamitulu woreda are constructed during Hailessilese (at least 35 years ago) and the
Derge regime (about 20 years ago) mainly as a source of drinking water for domestic and
47
livestock. These community ponds were constructed well prior to the current massive
implementation of RWH.
The surveyed RWH schemes mainly harvest runoff from either natural catchment located
adjacent to the ponds or from roads, footpaths and cattle-tracks.
4.1.2 Current state of affairs
According to the surveyed farmers, most of the observed HH ponds were not performing
as intended in terms of storing/retaining harvested runoff. Farmers argued that the poor
performance was caused by high water losses mainly through seepage and evaporation.
Almost all surveyed farmers with unlined ponds reported seepage losses from ponds as
the critical issue. The unlined ponds retain the harvested water for up to one to two
months after the main rainy season (around October). Worst cases were reported by the
development agent of the Bulbula Kebele, Ziway woreda where the area is dominated by
coarse textured soils, most of the harvested water was lost almost immediately after the
rainy season. By contrast, concrete tanks and ponds lined with plastic were found
relatively effective in holding the harvested water for two to three months longer than the
than the unlined ones. Only few farmers reported that the poor performance was
attributed to the improper siting of the ponds which led to poor runoff harvest.
To reduce seepage losses, only few farmers were provided with the plastic sheet
promised by MoRAD. Surveyed farmers strongly suggest that water losses can be
reduced by lining the ponds either with plastic or cement. One innovative and skillful
farmer at Jewe Bofu Kebele with experience in both lined tanks and unlined ponds said
that the lined one could manage to hold the harvested water two to three months longer
than the unlined one. This farmer tried to reduce the seepage with some success in one of
his ponds by lining with what he called a ‘cost-effective method’, by combining cement,
sand and ‘kuyissa’(soil of excavated and piled by termite mounds) with the ratio 1, 2 and
5, respectively (Figure 10).
48
Figure 10: ponds lined by combining cement, sand and ‘kuyissa’
Also improper utilization of the plastic provided to farmers to reduce seepage losses was
observed, e.g. poor handling, use for other purposes, damage by animals and theft. One
farmer reported that his plastics were stolen twice.
Farmers in the Bulbula kebele, Ziway Woreda, indicated during informal discussion that
the high water losses through seepage, which they observed in the pond of the farmer
training center (FTC) for demonstration purpose contributed to their reluctance to adopt
the technology.
4.1.3 Use of harvested water
Though the use of harvested water varied from place to place depending on the household
priority; farmers in general use it for various purposes including drinking water for
animals, watering vegetable and only some use it for watering for trees. Some farmers
use the water for washing cloths, cooking and for making mud blocks. Some farmers use
the water for raising pepper seedling as in Aleaku Gubantaboke Kebele.
49
4.1.4 Productive purpose of RWH
In crop production RWH can serve two purposes, i.e. to raise horticultural seedlings
during the dry period preceding the main growing season and to provide water as
supplementary irrigation whenever there is a shortfall in water during the growing season,
especially near crop maturity (Desta 2004). It is with these above objectives that RWH
has especially been implemented in the study area for production of high value crops like
vegetables, cash crops and fruits.
Farmers indicated that the harvested water was not adequate to meet the crop water
requirements either to mitigate the dry spells or off-season irrigation. Farmers with
unlined ponds outlined that most of the harvested water in ponds is lost through seepage,
while farmers with concrete tanks indicated that the small storage capacity (i.e. 40–60
m3). The low performance of the RWH systems resulted in poor interest for adequate
maintenance which further reduces the already low storage capacity of the structures.
Farmers used to clean concrete tanks till two to three years after construction. One
woman farmer at Edo Kejele Kebele reported that she abandoned her concrete tank built
by the MoARD because the harvested water did not last until the crop was ready to be
harvested despite her tank holds water and is in a good condition with no crack during the
time of survey.
The type of water application method farmers used, applying the water either via unlined
canals or directily applying to the crops using cans, resulted in unnecessary water losses
which further aggravate the insufficiency of the harvested water. To improve the
performance of RWH in terms of water use efficiency, drip irrigation kits have been
promoted by the government. However, none of the surveyed farmers were provided with
the drip irrigation kits.
Because of the problems discussed, most surveyed farmers were disappointed in RWH
and abandoned the technology for supplementary irrigation which in turn has led to low
adoption by non-beneficiary farmers. Most beneficiary farmers have shifted from using
50
the water for supplementary irrigation to other uses like drinking water for animals and
domestic use.
4.1.5 Operation and maintenance
Once the RWH physical structure is in place, it is normally the responsibility of the
owner to carry out operation and maintenance. Many of the surveyed ponds function
below their potential only because the owner failed to accomplish his responsibility. This
is more serious in community owned ponds. The observed problem in this regard is that
ponds and tanks were not repaired and maintained, tanks were not any longer covered
because roofs were stolen (Figure 11) or used for other purposes leaving the tank open
(Figure 12) and ponds were left unprotected allowing livestock to drink directly from the
pond (Figure 13).
The beneficiaries still consider that the one who constructed the system (Government or
NGOs) is responsible to repair and maintain the system. One good example in this regard
is that many of the treadle pumps (used as lifting device) supplied to farmers were
malfunctioning only because farmers were waiting for lubricating oil from the
government or NGOs while it would literary cost them few birr to buy oil from a nearby
town.
Figure 11: The corrugated sheet were stolen
Figure 12 the owner used the corrugated sheet
for other purposes and left the tank open
51
Figure 13: this pond was left unprotected and
livestock was drinking directly from the pond
4.1.6 The best option?
Obviously, RWH is one option to irrigate and produce high value crops to reduce poverty
and food insecurity. The assumption is that producing high value crops enables farmers to
get returns from selling the product and thus increasing the ability of farmers to generate
income. However, form this survey it is not clear under which conditions/scenarios RWH
can contribute to income generation. From the start, farmers were advised to use the
harvested water for supplementary irrigation to produce high value crops like vegetables
so that the family could benefit from selling the product. However, most surveyed
farmers are disappointed in the RWH interventions as their expectations were not
fulfilled. Only few farmers still use the RWH structure to irrigate tiny plots to produce
vegetables for home consumption and to raise pepper seedlings. The main reasons are
that much of the harvested water is lost through seepage and thus it is not sufficient and it
is very labour intensive to irrigate the whole fields by pumping the water manually from
the pond and applying directly to the crop.
There are, however, some positive experiences. For example, in Aleaku Gubantaboke
Kebele (Bulbula Wereda) some farmers have clearly confirmed the importance of RWH
as best option for pepper (seedling) production. Realizing the importance of pepper in
52
terms of cash return, some farmers have already shifted from maize, teff and wheat to
pepper. Three surveyed farmers used the harvested water to raise pepper seedlings which
they later transplant to the main field when the main rainy season starts. They reported a
net return of 10,000 birr per quarter hectare. They also sell seedlings to other non RWH
farmers if they have more seedlings than they need for themselves. They get 150 to 200
birr per seedling bed with a size of approximately 1 by 1.5 m. Pepper production is only
possible when there is rain in April to raise seedlings, otherwise famers shift to either
maize, teff or wheat. It is often rare for the area to have rain in April according to the
surveyed farmers. During the survey year (2009), too, there was not sufficient rain in
April as confirmed during the survey. Thus RWH may play a role by storing water till
April either the rainwater that came during last rainy season (implying a storage period of
six month) or capture the early rains in April (not frequently happening). The problem,
however, is that the ponds with water from the last rainy season are generally dried up
when it is needed for preparing the seedling. The problem is aggravated by farmers’ use
of the harvested water for other purpose (washing clothes, cattle drinking etc).
One industrious farmer from Jewe Bofu Kebele has devised an exemplary scenario. He
uses the harvested water for producing ‘Gesho’ (Rhamnus Pridoides), Pigen pea
(Cajanus cajan) and Alfalfa (Medicago sativa) seed. He gets a lucrative income from
selling Gesho by taking it directly to the market and the Alfalfa seed to NGOs. He got
500 birr from a kilo of Alfalfa seed. He also uses the water for sheep fattening and
poultry. But the two plastic sheets to cover his pond which were denoted by the Woreda
Agricultural office and NGO were stolen. He is now using his two RWH structures for
some time after the rainy season is stopped and both his RWH structures were almost
empty at the time of survey (Figure 14 and Figure 10).
Therefore, finding options to avoid/minimize water loss through seepage and evaporation
and encouraging farmers to develop innovative uses of the harvested water such as the
described examples should be the way forward to make better use of the the potentials
that RWH provide.
53
Figure 14: pond at Edo kejele kebele with no
water
Figure 15: RWH used for raising pepper seedling
at Bulbula Wereda, Aleaku Gubantaboke kebele
4.1.7 Lifting mechanism
Harvesting and storing the rainwater is not sufficient if the harvested water is meant for crop
production. The harvested water should be pumped from the storage to make it available for
the crop. Most surveyed RWH farmers were provided with a foot operated treadle pump by
MoRAD and different NGOs, to pump the water from ponds and tanks. The water is applied
either via unlined furrows to the crop or pump the water to small surface depression and
then directly apply the water to the crop by cans. However, much of the treadle pumps are
not functioning due to poor manufacturing and shortage of lubricants. Those farmers who
still use RWH structure are forced to use hand watering using old cans and applying the
water directly to the crop. This type of water application as reported by the farmers is
laborious and time-consuming. Moreover, it is inefficient in terms of using the scarce water
with much loss which consequently led to poor water management. Few farmers use chain
and washer type of pumps.
4.1.8 Farmers’ involvement during implementation
During the recent extensive implementation program of RWH, farmers were not consulted
on their needs and preferences and about the benefit to be generated. During field surveys,
farmers were seen short of proper understanding of the technology and some farmers
54
became skeptic regarding the benefits they could generate using RWH. Moreover, the
pressure from the implementers’ side to adopt the technology further aggravates the
farmers’ reluctance towards the technology. The pressure to use RWH resulted in a low
motivation of farmers to use RWH despite some of structures (most tanks) were in good
condition during the time of visit. For instance one innovative woman farmer was told by
Woreda agricultural office to construct a tank and she was provided with the necessary
material like cement, corrugated sheet and wood. She used the structure for three years to
produce vegetables like cabbage and onion and also to water trees. However, she lost
interest since a nearby farmer was provided with a shallow well by MoARD. She prefers a
well over a RWH tank because its supply of water is more reliable. Therefore, farmers’
preference must be assessed and farmers should thoroughly be told the befits as the success
often depends on it.
4.1.9 Community ponds
Community managed ponds are common in some Woredas such as Bulbula, Suro, Edo
Kejela, Zeleku Golanita Kebele. The community ponds in Suro and Zeleku Golanita Kebele
were constructed during Hailessilese (at least 35 years ago) and Derge regime (about 20
years ago) and the other were constructed around four years ago mainly for drinking water
of livestock and people. Most of them have a serious siltation problem because of improper
operation and maintenance.
Two nearby community ponds in Suro Kebele, one for domestic use and the other for
livestock, suffered both from a serious siltation problem. The community used to clean the
ponds at least every year; however they stopped around 10 years ago. This has led to almost
complete siltation of the pond for livestock. The silt traps provided with the ponds are not
serving any longer because they are too small in relation to the amount of runoff and easily
fill up with silt. In such community ponds equal importance in the design and
implementation must be given to the socioeconomics and physical structure. As well-
functioning of such ponds requires full participation of the entire community and thus strong
community organization is required to mobilize labour for operation and maintenance. In
55
general, farmers are easily mobilized for the initial construction as most felt the problem and
being excited to be relived from the problem. However, it is difficult to motivate and
mobilize farmers for operational and maintenance work. Thorough understanding of the
socioeconomics of the community is required to device mechanisms and instruments to
organize communities (local association) which will enable the sustainable management of
such ponds.
4.2 Identification of potential RWH areas in the CRV
The process of identifying suitable RWH was implemented in the ArcGIS model
environment using the model builder of ArcGIS 9.3. The suitability model generated
suitability map for RWH by integrating different input criteria maps using MCE. Different
spatial analysis tools were incorporated in the model to solve various spatial problems in the
process of identifying suitable areas. The identification process in this study was considered
as a multi-objective and multi-criteria problem.
The survey results and literature review indicated that most of the constructed ponds have
considerable seepage problems. In addition, most surveyed ponds could be filled with two or
three showers confirming that the catchment is no problem. Therefore, it was concluded
that, soil texture being responsible for seepage, was more important than the other criteria
which in turn result in a higher weight for soil texture.
The suitability model generated two suitability maps for ponds and in-situ RWH each with
five suitability classes, i.e. Very high, High, Moderate, Low and Very low suitability. The
spatial distribution of the suitability map for ponds (Figure 22) showed that the eastern and
western part of the study area dominated by cultivated land cover types is in very high (red)
and high (green) suitability category. The central and northern part is mostly moderate
suitable whereas the northwestern and some central part surrounding Lake Shala and
Abiyata has a low suitability. According to their acreage, 4 and 44% of the study area has
very high and high suitability for ponds, respectively, while 25, 18 and 1% of the area has a
moderately, low and very low suitability, respectively (Figure 16). The majority of the areas
56
with very high to high suitability have slopes between 2 and 8% and with an intensively
cultivated land cover. The major soil type in the very high and high suitable area is clay,
clay loam and loam with fine and medium texture and the rainfall ranges from 800 up to
1000 mm.
On the in-situ side, the spatial distribution of potential areas (Figure 23) showed that there is
no any very high suitable area whereas high suitability occurred in most part of the study
area except southern and western part. The northern and southern part is mostly moderately
suitable whereas the central part has a low suitability at few places. The area with very low
suitability for in-situ RWH can be neglected. According to their acreage, 60% of the study
area has a high suitability followed by 32 and 1% of the area with a moderate and low
suitability, respectively (Figure 17). The majority of the areas with high suitability have
slopes between 2 and 8% and the land cover is intensively and moderately cultivated. The
major soil type in this area is sandy loam, clay loam and loam with fine to medium and
medium to coarse texture and the rainfall ranges from 700 up to 1000 mm.
Pond
Suitability level
Very low Low Moderate High Very high
% o
f the
tota
l are
a
0
10
20
30
40
50
60
Figure 16: Percent of the study area per each suitability
level for pond
In-situ
Suitability level
Very low Low Moderate High Very high
% o
f the
tota
l are
a
0
10
20
30
40
50
60
Figure 17: Percent of the study area per each
suitability level for in-situ
One of the criteria for identifying potential areas for RWH was land cover type. Not all land
cover types are suited for RWH as RWH system meant for crop production should be close
to agricultural areas. It was with this reason that cultivated lands (intensive and moderate)
57
were given higher ranks than the other land cover types. This resulted in higher percentage
of very high to high suitability level to be under intensively and moderately cultivated areas
for both pond and in-situ RWH. The classification of suitability level per land cover type
expressed as a percentage of each land cover type is presented in Figure 18 and Figure 19
for pond and in-situ respectively.
To identify which Woreda is more suited for RWH, the pond and in-situ suitability map was
overlayed with the Woreda boundary map. The majority of the very high and high suitable
areas for pond RWH are in Degeluna Tijo, Tiyo, Munessa, Limuna Bilbilo, Ziway dugeda
and Meskan Woreda sharing 21, 16, 15, 13, 9 and 9% of the total very high to high suitable
areas , respectively. Kondaltiti, Kokir Gedbano Gutazer, Ezha, Akililna Mohr, Adami Tulu
Jido Kombolcha, Gumer, Seden Sodo, Dalocha and Alicho Woriro Woredas have almost no
land which is very high to high suitable for RWH ponds (
58
Table 10 and Figure 20). With respect to suitability level within the Woreda, the majority of
the land of Tiyo (99%), Hitosa (93%), Degeluna Tijo (93%), Limuna Bilbilo (85%) and Silti
(83%) Woreda are very high to highly suitable followed by Kofele (71%), Meskan (69%),
Lanfero (66%), Mareko (63%), Munessa (60%) and Alicho Woriro (58%) (
59
Table 10 and Figure 21).
The majority of very high and high suitable areas for in-situ RWH are in Degeluna Tijo,
Ziway Dugda, Adami Tulu Jido Kombolcha, Tiyo and Limuna Bilbilo Woreda sharing 18,
15, 14, 12 and 11% of the total very high to high suitable areas, respectively. Alicho Woriro,
Seden Sodo, Dalocha, Akililna Mohr, Ezha, Gumer, Kokir Gedbano Gutazer and Kondaltiti
Woredas have almost no land classified as very high to highly suitable (
60
Table 10 and Figure 20). With respect to suitability level within the Woreda, the majority of
the land of Gumer (100%), Tiyo (99%), Hitosa (94%), Degeluna Tijo (98%), Hitosa (91%)
and Limuna Bilbilo (90%) Woreda is very high to highly suitable for in-situ RWH followed
by Ziway Dugda (75%), Mareko (64%), Dugda(64%), Alicho Woriro (61%), Adami Tulu
Jido Kombolcha (61%), Lanfero (59%) and Kofele (55%) (
61
Table 10 and Figure 21).
The very high and high suitability for both ponds and in-situ RWH occurred together in 39%
of the study area mainly in eastern and southern part.
62
Land cover types
Shrublan
d
Moder
ately
Cul
ti
Inte
nsive
ly Cu
lti
Grass
land
Marshlan
d
Fores
t
Expos
ed S
urfac
e
Woo
dland
Afro-A
lpin
e
% o
f sui
tabi
lity
leve
l
0
20
40
60
80
100
Very lowLowModerateHighVery high
Figure 18: Distribution of pond suitability level per land cover type
Land cover types
Shrub
land
Ž�de
ratel
y Cult
i
Grass
land
Marsh
land
Forest
Expos
ed S
urface
Woo
dland
Afro-A
lpine
% o
f sui
tabi
lity
leve
l
0
20
40
60
80
100
Very lowLowModerateHigh
Very High
Figure 19: Distribution of in-situ suitability level per land cover type
63
Table 10: Very high and high suitability level per Woreda
Pond RWH In-situ RWH Woerda name Area
(km2) Very high and high suitability area (km2)
% of Woreda area
% of total very high and high suitability
Very high and high suitability area (km2)
% Woreda area
% of total very high and high suitability
Kofele 257 183 71 4 141 55 2 Limuna 630 536 85 11 568 90 9 Arsi Negele 1282 156 12 3 455 35 8 Munessa 1044 627 60 13 484 46 8 Dalocha 12 5 45 0 3 26 0 Degeluna Tijo 942 872 93 18 922 98 15 Lanfero 139 91 66 2 82 59 1 Tiyo 649 645 99 13 644 99 11 Silti 343 285 83 6 129 38 2 Adami T. Jido 1153 0 0 0 707 61 12 Gumer 0 0 0 0 0 100 0 Alicho Woriro 32 19 58 0 20 61 0 Mareko 323 202 63 4 207 64 3 Hitosa 245 229 93 5 226 91 4 Meskan 547 375 69 8 190 35 3 Ezha 5 0 0 0 0 2 0 Akililna Mohr 19 0 0 0 0 3 0 Ziway Dugda 1071 380 35 8 801 75 13 Dugda 724 111 15 2 461 64 8 Kokir 17 0 0 0 0 0 0 Sodo 735 265 36 5 92 13 2 Kondaltiti 40 0 0 0 0 0 0 Seden Sodo 57 13 23 0 11 20 0
Woreda
Kofele
Limun
a Bilb
ilo
Ars i N
egel
e
Mun
essa
Daloch
a
Degelu
na T
ijo
Lanfer
oTi
yo Silti
Adami T
. Jid
o K.
Gum
er
Alich
o W
oriro
Mar
eko
Hitosa
Mes
kan
Ezha
Akilil
na M
ohr
Ziway
Dugda
Dugda
Kokir
G. G
utaz
er
Sodo
Konda
ltiti
Seden
Sod
o
% fr
om th
e to
tal s
tdy
area
0
2
4
6
8
10
12
14
16
18
20
PondIn-situ
Figure 20: Percent of very high and high suitability per Woreda area.
64
Woreda
Kofele
Limun
a B
ilbilo
Arsi N
egele
Mun
essa
Daloch
a
Degelu
na T
ijo
Lanfe
roTiyo Sil t
i
Adam
i T.
J ido K
.
Gumer
Alich
o W
oriro
Marek
o
Hitosa
Meska
nEzh
a
Akililn
a Moh
r
Ziway
Dug
da
Dugda
Kokir G
. Guta
zer
Sodo
Konda
ltiti
Seden
Sod
o
% fr
om W
ored
a ar
ea
0
20
40
60
80
100
120
PondIn-situ
Figure 21: Percent of very high to high suitability for each Woreda per total very high and high suitability
area.
Since in most areas of the study area in-situ RWH is not practiced, criteria weight
assignment for in-situ was not supported with information from the field survey and only
based on the literature. Therefore another suitability map was generated with criteria
given equal percent of influence (Figure 24). This suitability map shows that 1 and 65%
of the study areas have very high and high suitability, respectively, while 24, 3 and
almost 0% of the study area has a moderate, low and very low suitability, respectively. In
general the same areas that appear as suitable for in-situ RWH in Figure 23 (using
different weight for the criteria) also appear in Figure 24 (with equal weight for the
criteria).
65
Figure 22: Pond suitability map
Figure 23: In-situ suitability map
Figure 24: In-situ suitability map with criteria given equal weights
4.3 Validation
Validation of the surveyed RWH was done using information obtained from the field
survey and the generated suitability map. The validation consisted of comparing the
generated suitability map and the location of the surveyed RWH structures using
proximity analysis tool of ArcGIS 9.3. For the purpose of the validation, the surveyed
RWH were first rated in two categories; successful and unsuccessful. From the result of
the field survey, most of the surveyed RWH structures were proved as having various
66
problems and categorize in the unsuccessful category. The assumption made during
validation was that if these RWH structures which were categorized as unsuccessful
category is found in non suitable areas in the derived suitability map, the result from the
suitability model would be proofed as good.
From the proximity analysis result, most of exiting RWH structures categorized as
unsuccessful (53%) were within the moderately suitable areas followed by low suitable
(43%). Only 3 % are with highly suitable areas. The fact that most of exiting RWH
structures categorized as unsuccessful are not found in the very high and high suitability
level in the derived suitability map indicated that the generated suitability map indeed
identified reliably the potential areas for RWH technologies. The validation results
showed that the database and methodology used for developing the suitability model
including the suitability levels of the criteria and the criteria’s relative importance
weights have given good results.
67
5. CONCLUSIONS AND RECOMMENDATIONS
The adoption and widespread replication of any RWH is extremely risky without any ex-
ante assessment or screening of the possible effects under the new physical conditions.
The failure or poor performance of many RWH structures in Ethiopia and in the study
area in particular can be partly explained by the improper selection of intervention areas.
A number of manuals for RWH implementation are available to assist in site selection
and the type and design of RWH in relation to the physical criteria. This has given
important lesson that suitability assessment should be given more attention. Maybe due to
the hasty implementation of many RWH interventions, often driven by the need to satisfy
Woreda specific RWH quota, the guidelines of such manuals are not followed. This has
been confirmed by the field survey and literature review. The results are an improper site
selection locating ponds in areas with less suitable soils, improper design (only one type
of tanks and ponds are constructed everywhere), lack of farmer involvement during the
planning and implementation, lack of materials like plastic sheet to reduce seepage in
ponds and lack of maintenance. This report, however would like to stress that the RWH
technology by itself may be the suitable but that the bottleneck is the planning,
implementation and management. RWH has brought many success stories from some
parts of the country (Chala et al. 2004; Rämi 2003) and in other parts of the world (Li et
al. 2000; Ngigia et al. 2005). The government and NGO’s appear to stimulate RWH with
unbelievable speed but forgot that proper interventions need time for location-specific ex-
ante assessments, consultation with of stakeholders and training of farmers in
management and governance (especially for community based ponds).
Utilizing runoff in an efficient and sustainable manner is crucial to improve the
performance of rainfed farming in the CRV. RWH is one option to use runoff better by
capturing and storing when rainfall is abundant for periods when water is scarce.
Providing information on the suitability of areas for different types of RWH interventions
is an important step prior to the actual planning and implementation. Identifying potential
areas for RHW requires spatial knowledge on a number of critical physical factors such
as soil, climate, topography and landuse. In this study the identification of potential areas
68
was done using GIS-based suitability model using the ArcGIS 9.3 model builder. The
suitability model used a MCE process that combined different biophysical factors: soil
texture, soil depth, climate, slope, land cover and groundwater depth. However,
socioeconomic factors (e.g. market access, infrastructure, population density) which are
also necessary for a complete assessment of the suitability of land for RWH were not
considered due to lack of readily available data for this large area. It is therefore
recommended to include such socio-economic factors in future studies to improve the
suitability assessment.
The suitability model generated two suitability maps; one for ponds and one for in-situ
RWH. Based on the pond suitability map, 4, 44, 25, 18 and 1% of the study area has very
high, high, moderate, low and very low suitability, respectively. For in-situ, 60, 32 and
1% of the study area has high, moderate and low suitability, respectively. The result from
the suitability model was validated using information obtained from field survey. The
validation results showed that the database and methodology used for developing the
suitability model including the suitability levels the criteria and the criteria’s relative
importance weights have given good results.
In this study, GIS was proved to be a flexible, time-saving and cost-effective tool to
screen large areas for their suitability of two types of RWH intervention. The suitability
maps provide an easy to understand source of information to quickly identify areas that
are more promising than other areas for RWH intervention. Such information is helpful
for decision-makers and planners, but one should be careful in the interpretation of the
generated information. Actual RWH implementation should always be preceded by a
field survey as the spatial resolution of the analysis does not guarantee that every location
in an area classified as highly suitable is indeed highly suitable for RWH. Vice versa, also
in low suitable areas there may be spots that can be suitable for RWH. Apart from this,
on-the-ground work is also needed for getting the socio-institutional setting of the area to
help complete the work as indicated before. The analysis as presented, however, provides
a first valuable screening of large areas and can be modified easily to incorporate other
criteria or information with other spatial resolutions.
69
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APPENDICES
I. Questionnaire on assessments of Rain Water Harvesting (RWH) in CRV
1. General Information
1.1. Date of interview: ______________________________ 1.2. Name of the farmer: ____________________________ 1.3. Village_________________ Woreda________________ 1.4. Administrative Zone________________ 1.5. Altitude:___________Location (Coordinate):__________
2. Household characteristics
2.1. Household head:
2.1.1. Male____ Female______ 2.1.2.Age______ 2.1.3 Level of formal education:____________ 2.1.4. Number of household members__________ 2.1.5 Number of adults (> 17 Yr.):_______ Children_________
2.1. Total farm size___________ 2.2. Land tenure of farm Own_____ Family_______ Own/ Family_____ Share cropping______ Rent______ Borrow______
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3. Water harvesting practices and status
3.1. What type of water harvesting structure do you have? _____________________ 3.2. By whom it was constructed? ________________________________________ 3.3 When did you start to use the structure?_________________________________ 3.4 For what purpose do you use the structures?
Crop production ________________
Animal fattening _______________
Drinking water ________________
Others _______________________
3.4 Size of the structure (appx.)?_____________________________ 3.5 Have you experienced problem while you use it? Yes:____ No:____
If yes, The Problems ________________________________________________ ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
3.7 Do you have success story?
Yes:____ No:____ If yes ______________________________________________________________
________________________________________________________________________________________________________________________________________________________________________________________________________________________ 3.8 Is the harvested water is sufficient for supplementary irrigation?_________________
Yes:____ No:____
If No_______________________________________________________________ _______________________________________________________________
3.9 What type of water lifting mechanism you used? ____________________________
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3.10 Initial investment cost(if you know)? _____________________________________ 3.11 Have you ever made maintenance work?
Yes:____ No:____ If Yes how what type and how often ____________________________________ ___________________________________________________________________
If No why?_______________________________________________________ ___________________________________________________________________
3.12 Any maintenance cost you incurred? ______________________________________ 3.12 Do you experience any difficulties to market your products? 3.13 General remark __________________________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________________
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II. Suitability Model A/ Soil texture
77
B/ Soil depth
78
C/ Slope
79
D/ Rainfall surplus
80
E/ Land cover
81
F/ Groundwater depth
82
G/ Overlay operation for ponds
83
H/ Overlay operation for in-situ
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