GIS - Based Physical Land Evaluation for Surface Irrigation System; Case Study of Walga Sub Basin, Oromia, Ethiopia.

Abstract

Irrigation development could improve agricultural productivity and enhance socioeconomic development of the community. Though agriculture is the leading sector, most of Ethiopia’s cultivated land is under rain fed agriculture. Rainfall variability and inadequacy have been challenging the sector due to local and global environmental changes. This study was aimed to evaluate suitability of Walga sub basin for surface irrigation development and producing geo-referenced map of potentially irrigable sites. Suitability of the area’s slope, soil, land use land cover and surface water resources were evaluated and geo-referenced map of each parameter were presented on Arc GIS. Overall suitability map of the area for the intended irrigation method was produced using suitability model developed on Arc GIS. In the suitability’s model weighted overlay analysis, high weight was given for slope, since it is the determinant factor in the evaluation of the given area for surface irrigation development. Result of the suitability model revealed that about 45.72% (135519.18 ha) of lands in the sub basin were in the range of highly suitable to marginally suitable for surface irrigation development due to the combined effect of slope, soil and land use land cover suitability. Potentially suitable sites for surface irrigation development were evaluated for the selected crops (Maize, Soyabean and Sesame). By maintaining 20% of the stream flows for downstream ecological balance, flows in each stream are able to satisfy gross irrigation water requirements of the selected crops in the potentially irrigable sites. Accordingly; Amanya, Rebu, Kulit, Nano, Walga and Darge river catchments have a total potentially irrigable areas of 41.32 % (122488.2 ha) together in the sub basin through surface irrigation system. The current study considered slope, land use land cover, surface water availability and some soil physical properties only. Other suitability factors like socioeconomic, environmental issues, soil chemical properties and others should be studied in detail for sustainable irrigation development in the area.