GIS BASED SURFACE IRRIGATION POTENTIAL ASSESSMENT OF RIVER CATCHMENTS FOR IRRIGATION DEVELOPMENT IN NORTH GOJJAM ABBAY BASIN

Abstract

Assessing available land and water resources for irrigation is important for planning their use. Main objective of this study was assessing the water and land resources potential of river catchments in North Gojjam for irrigation development and generating suitable map of these resources by using Geographic Information System. Watershed delineation, identification of potential irrigable land, and estimation of irrigation water requirement and surface water resources of river catchments were the steps that are followed to assess this irrigation potential. To identify potential irrigable land, irrigation suitability factors such as soil type, slope, land cover/use, and distance from water supply (sources) were taken into account. The irrigation suitability analysis of these factors indicate that 40.5% of slope, 53.72% soil and 94.4% of land cover/use in the study area are in the range of highly suitable to marginally suitable for surface irrigation system. Using pair-wise comparison method, overall weighted overlay analysis of these factors gave potential irrigable land among suitable land are 5%. There are four (maize, onion, potato and pepper) crop were selected under identified irrigable area and their gross irrigation demand calculated by using nearby climatic stations. The result revealed that irrigation requirements of 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 area-ratio method and results were obtained on monthly bases. By comparing gross irrigation demand of irrigable land with available flow in rivers, total surface irrigation potential of the study area was obtained as 9,503 ha. Since the suitable land for surface irrigation is very small, due to the scarcity of water. It is possible to increase surface irrigation potential by increasing available water using storage structure.