GIS BASED ASSESSMENT OF SURFACE IRRIGATION POTENTIAL AND LAND SUITABILITY FOR GEBA WATERSHED, WABI-SHEBELE RIVER BASIN, ETHIOPIA

Abstract

Assessing available land and water resources for irrigation is important for planning their use. The study was focused on investigating land and water resources potential of Geba watershed 138096ha found if five woreda (Deder, Chelenko, Kersa, Badeno and melkaballo) and preparing geo-referenced maps of these resources using Geographic Information System. The discharges at un-gauged sites were estimated from gauged sites by applying runoff coefficient method and results were obtained on monthly bases. 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 irrigable land of the area was identified using weighted overlay analysis of the suitability parameters. To grow on these identified irrigable areas, four crops such as Maize, potato, wheat and cabbage were selected and their gross irrigation water demand calculated by using nearby climatic stations. By comparing gross irrigation water demand of irrigable land with available flow in river physical surface irrigation potential are determined. The irrigation suitability analysis result of these factors indicate that soil suitability 100516.26ha (72.78%) is suitable and 37579.74ha (27.22%) not suitability for surface irrigation, Land use land cover 126960.6ha (91.6%) suitable and 11535.4ha (8.4%) not suitable for surface irrigation, slope suitability 66895.85ha (48.44%) is suitable and 71200.15ha (51.56%) not suitability for surface irrigation. Euclidean distance from river 135804.76ha (98.35%) is suitable and 2291.24ha (1.66%) not suitability for surface irrigation. By considering outlet of diversion structure weighted overlay analysis of these factors total irrigable land 58497.56 ha (66.3%) suitable and 29738.44 ha (33.7%) is not suitable for surface irrigation. finally, by comparing minimum available flow with gross irrigation requirement physical irrigation potential of Geba watershed out of 58497.56ha only 25637.56ha (43.83%) are suitable and 32860ha (56.17%) are not suitable for surface irrigation. Therefore, the researcher recommends other researchers to conduct different water resource researches on this river in order to increase the suitable irrigable land, suitability analysis for other methods of irrigation such as sprinkler and drip irrigation should be carried out.