ASSESSMENT OF ROAD SIDE CATCHMENT SURFACE RUNOFF FOR SPATE IRRIGATION IN GATO-YANDA WATERSHED, RIFT VALLEY BASIN, ETHIOPIA

Abstract

Road side catchment surface runoff is one of surface runoff generated from small catchments around road side during rainy event time and can be used as a source of water for spate irrigation mainly from culverts along the road side. The main objective of this study is to assess road side catchment surface runoff potential of the road from Arba Minch to Konso in GatoYanda catchment for spate irrigation in order to improve the productivity of rain fed agricultural system in the area. For this study, primary data such as culvert geographic location and agronomic (type of crop dominantly cultivated in study area) were collected through field visit whereas, secondary data such as meteorological and hydrological data were collected from NMSA and MoWIE respectively. Hydrological model HEC-HMS was used to simulate inflow for each culvert catchments. The model calibration was made at Kulfo near bridge by using 1996-2002 hydro-meteorological data and re-evaluated by transferring the optimized parameters in to Gato River near bridge by using 1990-1993 hydro-meteorological data. The overall performance of the model has shown good performance. Out of twenty-two culverts identified along the main road, only seven culverts with a minimum of 4.5 km 2 were selected and used for this study. Accordingly, based on the flow generated by using HEC-HMS, on average a total flow of 1.46 m 3 /s per annum was obtained from the seven selected culverts. The irrigation water requirement was estimated by using CROPWAT 8.0. The dominant crop types cultivated in the study area was Sorghum and Maize covered small area. Based on this, irrigation scheduling was made for 75% and 25% irrigation land coverage for Sorghum and Maize respectively. In general, more than 3860 ha of irrigable land can be cultivating by using the road side catchment surface runoff by using the intended cropping pattern.