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UNESCO-IHE Institute for Water Education, Delft (2009)

Optimizing land and water productivity in the Lah sub-basin, Ethiopia

Ashebir, M.S.

Titre : Optimizing land and water productivity in the Lah sub-basin, Ethiopia

Auteur : Ashebir, M.S.

Etablissement de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2009

Résumé
Accounting for 57% of gross domestic product (GDP) and 86% of the labour force, agriculture remained in 2009 the economy’s most important sector of Ethiopia. Rainfed crop cultivation is the principal activity and is practiced over an area of 27.9 million hectares (ha), or approximately 23% of potentially arable land. Frequent and severe droughts, low productivity and less production cause serious decreases in the incomes of rural inhabitants who tend to rely heavily on rainfed agriculture. While estimates have shown that up to 3.7 million ha can be irrigated, a mere 300,000 ha of irrigation has so far(2009) been developed. Traditional practices influence the irrigation agriculture. Amhara Region is one of the eleven political administrative regions where this study is carried out. Agriculture is the main income source of the people. Erratic rainfall, land degradation and high population pressure brought about low production and productivity. The main objective of this MSc study is to identify and evaluate technical and institutional measures for optimizing land and water productivity in the Lah sub-basin. The approach and methodology of the study follows a sequential pattern starting from delineating the basin boundary from digital elevation models (DEM). Then followed by digitizing the land use planning maps from Google earth, soil survey for textural classification, assessing the basin land and water potential, studying the agricultural production and practice, studying the existing institutional set up and finally modelling the irrigated agriculture with the CROPWAT Model. It is found that the basin has area coverage of 738 km2, and three main drainage lines. These are Debohola, Lah and Geray. Due to improper management of land and water resources, the basin is subjected to soil erosion. The existing surface drainage condition is mainly dominated by the natural drainage systems. During the rainy season farmers drain their plots of land to the nearby lowest point to avoid waterlogging and top soil erosion. Since the practice is not systematically designed, it results in formation of gully erosion inside farmlands. Agro-climatically, the basin is classified into three categories. The cold zone (Dega),warm zone (Woyina Dega), and the hot zone (Kola), which respectively account 12%,87% and 1%. Even though the category based on altitude, it implicates the type of crops in each zone. Since the majority of the basin is under the warm zone, it is suitable for a variety range of crops. The main crops are Teff, Maize, Barley, Potato, Legumes, Orchard, pulses and oil seeds. The basin has eight land use units. Farmland unit covers 73%, stony bush land 16%,grazing land 10%. The rest is for small towns and water body. The farmland unite is classified in to four land suitability classes for agricultural consideration. It is found that12% is highly suitable land with a slope range of 0 - 2% ; 22% moderately suitable with aslope range of 2 - 4% ; 23% marginally suitable with a slope range of 4 - 6% and 43% is classified under not suitable land suitability unit and has a slope greater than 6%. All the irrigation systems except Debohola-1 and Debohola -2, are found under highly suitable to moderately suitable land units. Silt clay soil texture with reddish brown colour covers81% of the farmland. Out of the three drainage lines, Lah River is the only gauged river with an average yearly flow of 12.5 m3/s. However, during the dry season, the average flow of the River is only0.77 m3/s, which is used for the existing five irrigation systems (813 ha) and for other domestic use. The measured base flow for Debohola River is 0.27 m3/s, which is available for the 830 ha of existing irrigation system and for other water use. Geray has1.44 m3/s flows for an area of 1,042 ha. The peak irrigation water required for the actual area based on the existing cropping pattern and calendar is found 0.49 l/s in the month of February. The study discussed the existing institutional set up for irrigation and drainage development. Bureau of Agriculture and Rural development follow the political administrative set up. However, irrigation and drainage affecting factors follow the natural river basin. Lah sub-basin is intersected by four woredas : - Jabi Tehinan Woreda62%, Buri-Wonberima 21%, Sekela 15% and Banja 2%. The study recommends theestablishment of water user associations (WUA) following the main drainage lines : - one on Debohola River, two on Lah River and one on Geray spring. To link these WUAs with the existing political administrative institution, a Basin Irrigation and Drainage Federation (BIDF) is recommended. Finally, the study evaluates the basin efficiency with regard to the available land and water resources. It is found that the basin water use irrigation efficiency is only 3%. By implementing water harvesting technique and increase the basin efficiency to 7% it is possible to irrigate the highly suitable land unit and increase the irrigation production by 42%, or the total basin production by 77%.

Sujets  : land productivity ; water resources ; irrigated agriculture ; river basins ; Ethiopia

Présentation

Page publiée le 2 janvier 2017, mise à jour le 12 octobre 2018