IRRIGATION WATER POTENTIAL AND LAND SUITABILITY ASSESSMENT IN KURFA CHELE-GIRAWA WATERSHED, WABE SHEBELLE RIVER BASIN, ETHIOPIA

Abstract

Assessing available land and water resources for irrigation are important for planning their use. From a number of uncertainties, the watershed constrained that stream flows from some of the rivers are not known, potential irrigable areas in the watershed have not been identified and matched with the water requirements of some crops commonly grown in the watershed. It is therefore this study was initiated with the objective of assessing the water and land resources potential of river catchments in Kurfa Chele-Girawa watershed. Watershed delineation, identification of potentially irrigable land, and estimation of irrigation water requirement and surface water resources of river catchments were the steps followed to assess the irrigation potential of the study area. To identify potentially irrigable land, irrigation suitability factors such as soil type, slope, land cover/use, and distance from the water supply (sources) were taken into account. The irrigation suitability analysis of these factors indicates that 55.1 % of soil, 95.6 % slope and 93.7% of Euclidean distance in the study area are in the range of highly suitable to marginally suitable for a surface irrigation system and 88.6% of land cover/use are highly suitable. The weighted overlay analysis of these factors resulted that total surface irrigation potentially of the study area are 128,429.6 ha, from this, the potential irrigable land was obtained as 58,995.15 ha. To grow crops on these identified irrigable areas, two crops such as Maize and Potato were selected and their gross irrigation demand were calculated by using nearby climatic stations. The result has shown that irrigation requirements of the identified command area varies according to nearby climatic station and type of crops selected. The discharges at un-gauged sites were estimated from gauged sites by applying runoff coefficient method and results were obtained on a monthly basis. By comparing gross irrigation demand of irrigable land with available flow in rivers, a gross irrigation demand of potentially irrigable land of 58,995.15ha are not fulfill with the present flow, so providing a means of water storage above the potential command area are necessary.