GIS-BASED SURFACE IRRIGATION POTENTIAL ASSESSMENT IN UPPER BILATE WATERSHED, RIFT VALLEY BASIN, ETHIOPIA

Abstract

Irrigation is an important factor in improving food security by increasing agricultural production. The development of irrigation and water management for agriculture has a significant role in improving productivity and reducing vulnerability to climate change. This study was concerned with surface irrigation potential assessment in the Upper Bilate watershed using GIS. The study identified suitable land, crop water demand and supply for dominant crops grown in the watershed, and also produced suitability maps for surface irrigation development. To identify suitable land the land suitability parameters were used such as land slope, soil parameters, proximity to River and land use land cover. The suitability of each parameter was analyzed individually and then the weighted overlay analysis was to get the overall suitable land. The crop water requirement of wheat, maize and potato crops was identified by the CROPWAT8.0 model using climate data, soil data and crop data. The result of the weight overlay analysis revealed that 74.9% (148,424.5ha) of lands in the watershed were in the range of highly to moderately suitable for surface irrigation due to the combined effect of slope, soil, land use land cover and proximity to River suitability and 25.1% (49,668.43ha) of the area were unsuitable for surface irrigation. The comparison of stream flow with the gross irrigation water requirements for selected crops and identified suitable sites for surface irrigation. So, the irrigation potential of the Upper Bilate watershed was found to be 11300.96ha (7.64%) of the total suitable land in the watershed. To irrigate the remained suitable land of 137,123.5ha requires 393.62m3/s and to achieve it, a water storage structure is required. The identified surface irrigation potential assists policymakers in the development of irrigation projects. This study considered only slope, land use land cover, proximity to River and soil physical properties but other suitability factors like, socioeconomic, environmental issues, soil chemical characteristics and irrigation method should be studied.