GIS SUPPORTED INVESTIGATION OF IRRIGABLE LAND AND SURFACE WATER RESOURCES: A CASE OF ANDASSA WATERSHED, ETHIOPIA

Abstract

Investigation of potential irrigable land and available water resources is an essential for the development of irrigated agriculture. The study is focused on investigating land and water resources potential of Andassa river catchment and preparing geo-referenced maps of these resources using GIS. Land suitability for irrigation development was identified by considering the irrigation suitability factors such as slope, soil and land use /land cover. The analysis result of these factors indicates that 95.17 % of slope, 75.2 % of soil and 97 % land use/land cover are in the range of highly to marginally suitable for surface irrigation. The irrigable land of the area was identified using weighted overlay analysis of the suitability parameters. The total irrigable land of watershed is about 76.7% which is potentially suitable for surface irrigation and 23.3% is classified as nonsuitable (N). Surface water potential of the study area was estimated through stream flow simulations by SWAT model. The model was calibrated and validated from observed stream flow data of the watershed using the periods of 1992-2005 and 2006-2012 respectively leaving two years as “warm up’ ’period. During calibration and validation, the results of model performance indicators were in the acceptable range (R2 >0.6 NSE>0.5 and RVE<-10%) which indicated that a good agreement between observed and simulated values. Generally, surface water potential of Andassa watershed was estimated to be 45624.15ha of land for surface irrigation system without considering any storage structures. For sustainable irrigation development, other suitability factors such as soil chemical properties, socio-economic, environmental issues, and distance from water sources should be studied.