Suitability and scenario modeling to support soil and water conservation interventions in the Blue Nile Basin, Ethiopia
© Amdihun et al.; licensee Springer. 2014
Received: 8 April 2014
Accepted: 15 July 2014
Published: 19 September 2014
The widespread land degradation in Ethiopia has necessitated extensive soil and water conservation interventions over the last four decades. Despite these the degradation of land continues. The conservation interventions in most cases were, and still are, predominantly top-down approaches following government directives. The success of these blanket approaches has been limited and an alternative approach needs to be devised. This paper attempts to identify alternative options for selecting appropriate soil and water conservation technologies based on the biophysical suitability of the landscape.
The results of this study suggest that with appropriate soil and water conservation measures, it is possible to reduce soil loss within the Blue Nile Basin by up to 600 million tons 46% within 5-10. The statistics on net soil loss reduction also indicate that successful implementation of conservation measures in only four administrative zones (out of 17) can potentially reduce up to 60% of the total soil loss in the Basin.
Landscape level modeling of soil and water conservation has enabled identification of appropriate conservation measures that can are suited to particular biophysical niches. A targeted approach to soil and water conservation is more efficient in terms of both financing and labour, in contrast to the traditional blanket approaches of the past.
KeywordsSoil and water conservation Landscape suitability Soil erosion modeling, Blue Nile, Ethiopia
Land degradation reduces the productivity of agricultural land, and affects the livelihoods of millions of people.
In Ethiopia 84% of the population lives in rural areas and 95% of the livelihoods depends on subsistence small scale agriculture. Agriculture constitutes 46.6% of the national GDP and employs 90% of the rural population. The average agricultural land holding is nearly one hectare which hardly feeds the average 6.5 persons family size in rural areas (CSA ). This creates pressure on the natural resources reduces household income, and results in food insecurity. Eleni () have emphasized that soil degradation is one of the major environmental problems challenging agricultural production in many parts of Ethiopia and highlight the need for conservation action. Although various soil and water conservation interventions have been introduced across Ethiopia, land degradation, mainly in the form of soil erosion, continues to be a serious problem. Soil erosion is frequently cited as one of the most significant challenges to food security and future economic development of the country (Wagayehu and Lars ). Soil degradation is a growing problem in Ethiopia and a threat to any future agriculture based growth or `transformation'.
The Ethiopian Forestry Action Program (EFAP ) estimated that every year the Ethiopian Highlands lose between 1.9 to 3.5 billion tons of topsoil and every year 20,000 - 30,000 ha of cropland in the highlands is taken out of production as a result of soil erosion. This study also estimated that by 2010, some 10 million highland farmers' cultivation land would be destroyed if land degradation were to continue at the same rate.
State sponsored soil water conservation (SWC) efforts were begun after the 1970 catastrophic drought and famine. One of the contributions of this large scale intervention was the introduction large scale SWC interventions; both structural and afforestation programs. In total close to one million kilometer length of structures were constructed which had some beneficial effects but were not sustained after the downfall of the `Derg a regime for various reasons. Some of the common reasons often cited and relevant to this discussions are the use of force in implementing the SWC measures, insufficient participation of farmers in the planning of conservation alternatives and in decisions regarding the selection of technologies. Furthermore, the outcome of the interventions was not rewarding in the short term to farmers. All these were among the top reasons often cited for the failure over the last decades (Bewket ; Admassie ; Hurni , Kassie et al. ).
In order to be successful, soil and water conservation work needs to be participatory. Shiferaw and Holden () argued that conservation measures were traditionally undertaken without the involvement of the land owner. Farmers were not allowed to remove the structures once built although maintenance was often carried out through the Productive Safety Net Program (SNP) with farmer incentives. However, the practice has largely remained delivery oriented in which the farmers are forced to implement conservation measures designed for them by technical experts (Bewket ). Unfortunately, farmers experience of SWC techniques, coupled with their knowledge of the land they manage, are often ignored and bypassed in the current top-down approach to conservation. Mitiku et al. () criticized this approach where farmers have typically been offered one conservation package (e.g. terracing) rather than a choice of alternative practices (menu of options) from which to choose those that match their particular needs and circumstances (Admassie ; Nowak ).
Hurni () developed several possible scenarios and options, highlighting that sustainable land management involves more than mere technological development. Multi-criteria analysis has been used as an approach to combining the most significant factors in choosing appropriate soil and water conservation technologies. Various studies exist which demonstrate the practical application of multi-criteria analysis in natural resource management including for soil and water conservation (Prato and Herath ; Robert et al. , Geneletti ; Kiker et al. ).
The objective of this paper is to demonstrate a landscape level SWC planning approach based on multi-criteria spatial analysis. It is also intended to demonstrate the impacts of SWC technologies by out-scaling plot level studies to the bigger landscape (Blue Nile Basin). The major limitation of this work is that it did not consider social acceptance of the technologies assuming that applying the technologies to local settings requires further social considerations based on available resources and experiences.
Result and discussions
Proposed SWC measures
One of the focus areas of this research was to identify optimal SWC options for the different landscapes and land use systems of the Basin based on susceptibility to soil erosion. Some of the key points typically considered in SWC planning are the nature and level of degradation, the agroecology of the area, land use and land cover conditions, slope and soil types. Based on these five biophysical parameters, areas of the Basin are categorized under one of the proposed SWC interventions and a SWC. In total six major types of SWC interventions are identified and proposed for the different landscapes and soil erosion grades of the Blue Nile Basin.
Proposed major SWC measures and area coverage (Based on model results)
Proposed major SWC measure
Bench Terraces/Grass Strips
Level bund/Level fanya Juu
Graded bund/Graded fanya Juu
Controlled grazing /Revegetation/Cutoff drain
Area Closure/Tree planting
Must be changed to grassland or Forest land
With all of the proposed major SWC technologies there should be support practices that bring additional benefits to the soil erosion reduction and also add economic benefit to farmers.
Proposed support practices for the major SWC measures
Scenario analysis `with and `without SWC
Impacts of SWC measures in reducing soil loss and runoff (Source: Herweg and Ludi)
Relative impact on soil loss (%)
Relative impact on runoff (%)
Graded fanya juu
Level fanya juu
Graded fanya juu
Level fanya juu
Anjeni (28% slope)
Anjeni (12% slope)
A comparative field study by Yihenew et al. () demonstrated the difference between conserved and non-conserved land. A 9-year old soil bund, a 9-year soil bund stabilized with tree lucerne, a 9-year old soil bund stabilized with vetiver and a 6-year old soil bund stabilized with tree lucerne had 71.20, 68.56, 52.30, and 36.12%, respectively higher percent organic matter than the control treatment. The result agrees with the finding by Million () that organic matter content of three terraced sites with original slopes of 15, 25, and 35% were higher compared to the corresponding non-terraced sites of similar slope. A study conducted by Kinati () also showed that the organic matter content of non-conserved land for a slope range between 10 and 15% was lower than the terraced land of corresponding slope class. The practices also had a significant impact on the amount of infiltration. The non-conserved land demonstrated the lowest mean value of infiltration rate. Slope stabilization is also another advantage of SWC techniques.
Implications of the proposed SWC technologies (Based on model results)
Proposed SWC measure
% reduction in soil loss
Total soil loss reduction (tons)
Erosion statistics across administrative zones
Zonal soil erosion scenario `with´ and `without´ SWC (Based on model results)
% share from the total reduction
N. Shewa (R3)
N. Shewa (R4)
In addition to the on-site impacts which occur across the Ethiopian Highlands, siltation of downstream reservoirs is experienced in Sudan and Egypt. This shared problem needs shared interventions amongst these countries to abate the problem of land degradation in the upstream areas of the Blue Nile Basin. If proper SWC interventions are made according to the recommendations it may take 10–15 years to bring the extreme soil erosion to an acceptable level. By this, Ethiopia (now building a mega dam in the downstream of the Blue Nile Basin) and downstream countries (Sudan and Egypt) will benefit as the intervention significantly reduces siltation in the dams and reservoirs.
Finally, discussions of the positive impacts of SWC interventions at administrative zones helps to localize SWC proposals. Any of the administrative zones can consider the SWC recommendations based on the various biophysical criteria.
In the past the blanket application and `one size fits all´ approach, and top down implementation of SWC interventions have rarely been successful. The application of such interventions in the Blue Nile Basin should consider appropriate biophysical and socioeconomic parameters. In addition any SWC should consider technical feasibility, ecological soundness, economic viability and social acceptance before implementation. The focus of this study was to identify appropriate SWC proposals for the different landscapes of the Blue Nile Basin. Accordingly, soil erosion risk grades, land use/land cover, agroecology and slope are the four major parameters used to create homogeneous planning units to propose appropriate SWC interventions. GIS based raster calculations and overlay functions are used to propose six major SWC proposals.
Bench terraces/grass strips are proposed for 28% of the areas in the Basin and landscapes under this category include cultivated lands with moderate to high soil erosion risk. Level bund/level fanya-juu is proposed for 6.3% of the Basin predominantly in dominantly cultivated lands in the humid and sub humid areas that are experience high runoff. Graded structures (bunds or fanya Juu) are proposed for very high soil erosion risk areas under cultivation (14% of the basin). Those areas with extreme slope (>50%) are categorized under `must be changed to forestland/grassland´ with area closure and this constitutes 3.3% of the basin. Controlled grazing, revegetation and cutoff drain is proposed on open degraded and overgrazed lands (8.9% of the basin). Area closure/tree planting is proposed in 38.9% of the areas and the areas under this category are either woodland of the lowland areas that are under continued risk of deforestation or those highly degraded lands under open grass/shrub/wood lands. These SWC interventions need to be combined with support practices that can boost the effectiveness of each intervention.
A plot level study by Herweg and Ludi () on the effectiveness of the major SWC interventions is used to assign soil erosion reduction efficiency for each. Based on these plot level results the `with´ and `without´ SWC scenarios were analyzed and mapped. Results indicate that if the proposed SWC are implemented soil erosion can be reduced by 46% within five to ten years. The scenarios have also been analyzed for administrative zones. Results indicate that successful implementation of SWC intervention in only four zones (south Wollo, east Gojam, south Gonder and north Shewa (R3)) constitute 60% of soil loss reduction in the Blue Nile Basin.
The data presented here demonstrate that land degradation (in the form of soil erosion) can be minimized significantly if appropriate and large scale soil and water conservation interventions are carried out, which are tailored to the biophysical setting. The type of proposed intervention needs to be flexible to modify in accordance with local preferences and resource availability during implementation.
Location of the study area
Data and methods
Data for soil erosion estimate is adopted from the author's previous work (Amdihun et al. ). The land use layer is updated from the ARBIDMP () data at quarter a million scale. SRTM DEM Version 4 is used to calculate slope and agroecology of the Blue Nile Basin. Review of related literature on conservation planning alternatives is explored mainly from Ethiopian Highland Reclamation Study (EHRS ), Community Based Participatory Watershed Management Guideline (CBPWMG) by Lakew et al (), Abbay River Basin Integrated Development Master Plan Project (ARBIMPP ) document and the different published articles at plot level.
SLAI = Soil loss after intervention (5–10 years)
SLWOI = Soil loss `without´ SWC intervention
SLWI = Soil loss `with´ SWC intervention
The potential benefits of the major soil and water conservation in terms of reducing soil loss is discussed as the final synthesis of this SWC modeling work based on plot level study results on some of the major SWC measures. The different SWC planning alternatives are proposed and the respective advantages are discussed. Comparative assessments are also made on the `with´ and `without´ SWC scenarios.
The significance of such meso-scale modeling approach is that planners/conservationists do not miss the big picture in the small details like plots. Such multi-criteria based planning also helps to come up with comprehensive conservation planning for the landscape that takes the different layers in to planning consideration which are often lacking in the previous conservation interventions of Ethiopia.
The detailed conceptual methodology for data layer combination is given under Figure 9.
a `Derg´ means committee referring to the communist regime led by Mengistu Haile Mariam from 1974 to 1987.
AA: carried out the research work including the writing of the draft articles, data preparation, manipulation and analysis of the results. He has agreed to be accountable for all aspects of the work in ensuring that questions related to the paper. GE: contributed during the conception and design of the proposal and revising it critically for important intellectual content. He has been supervising the progress of the research. RL: have been involved from the inception of the research concept to proposal development. She also facilitates the funding from IWMI for field work. ZG: contributed in providing guidance starting from the proposal stage of the research commenting critically on the draft paper. He revisited it critically for important intellectual content. He also provided data for test plots of SCRP stations used in the erosion modeling. All authors read and approved the final manuscript.
Ahmed Amdihun is a Lecturer in Addis Ababa University in Geoinformation and Environmental modeling. EphremGebremariam (PhD) is an assistant professor in Addis Ababa University and he is a specialist for Geoinformation and Environmental planning. Rebelo, Lisa-Maria (PhD) is a senior Researcher in International Water Management Institute and specialist for Remote Sensing applications. Gete Zeleke (PhD) is a director and a specialist in soil and water conservation planning.
This research is jointly funded by Addis Ababa University and International Water Management Institute. Special credit goes to supervisors; Dr. Ephrem G., Dr. Lisa-Maria R. and Dr. Gete Z. and their respective institutions for their great contributions in this work. Individual experts all across the Blue Nile (Abbay) Basin also deserve appreciation for their relentless efforts and willingness to travel long distances with me during the field work.
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