ASSESSMENT OF IRRIGATION POTENTIAL FOR EXISTING RAINWATER HARVESTING STRUCTURES: CASE STUDY OF LAGA-SURE WATERSHED

Abstract

The first and foremost step in assessing land and water resource is to be certain about the extent of their potential, in water resource development. The present study is aimed at estimate potential surface runoff and identifying suitable areas for supplementary irrigation by existing Rainwater Harvesting Structures (RWHS) in the Laga Sure watershed that cover 85 square kilometers in Ganale Dawa River Basin. Runoff potential was estimated using the Soil Conservation Service Curve number method. Land evaluation was made from soil, slope, landuse/landcover and vicinity to water source point of view based on FAO land evaluation guideline for irrigation agriculture. The CROPWAT software was used to calculate the crop water requirement for selected dominant crops in the area, viz., maize. The result shows that, the runoff potential of Dhawa and Danbi-Korba sub watershed and the whole Laga Sure watershed is 1.034Mm 3 , 2.375Mm 3 and 11.887Mm 3 , respectively. Though the watershed has large runoff potentials, Dhawa and Danbi-Korba RWHS harvest 1.3% of it. The land evaluation result indicates that 71.85% and 69.3% of the study area are potentially suitable for sprinkler and surface irrigation system, respectively. The demand analysis reflects that 42.02% of harvested water is consumed by committed water use and atmospheric demand. The remaining 57.98% usable volume of water can be used for irrigation purpose. As a result, the selected RWHS have a potential to irrigate 29.11ha and 45.87ha by applying surface and sprinkler irrigation methods, respectively, on identified suitable land. Therefore, it can be concluded that the vastly available surface runoff is lost through direct runoff from watershed due to limited capacity of rainwater harvesting structures and the existing RWHS have irrigation potential, which has not been efficiently utilized in previous time. It is recommended that construction of new appropriate rainwater harvesting structures and rehabilitation of the existing one in the sub watershed could increase the irrigation potential of the Laga Sure watershed.