STATUS AND PROBABLE IMPROVEMENT OF SPATE IRRIGATION SCHEMES IN WALTANE WATERSHED, AWASH RIVER BASIN, ETHIOPIA

Abstract

Although the spate irrigation systemis an ancient practice, only in the past very few decades has the system undergone a few modernization interventions. However, these interventions were mostly in the aspects of heavy investment over sophisticated head works to improveflood water diversion efficiency. In many cases, modernization interventions were not successful due to various problems such as heavy sedimentation, high floods, and disturbed local water distribution rules.On the other hand, successful improvements incorporate less labor-intensive and relatively permanent structures with the advantages of conventional systems without considerably altering the approach of the spate irrigation practice. This study was initiatedto estimate surface runoff potential, land suitability evaluation for spate irrigation, and identify the status and problem of the waltane watershed for spate irrigation developmentand improvement. The surface runoff potential is calculated by the SWAT model. Specifically, the SWAT model was used to compute peak run-off, surface runoff potential of the waltane sub-catchment was assessed monthly, Based on monthly calibration, NSE was obtained to be 0.84, and R2 was 0.85, and the monthly validation, the R2 0.89 and NSE 0.86obtained, showing the capacity of SWAT model to ascertain the peak runoff every sub-basinover the watershed. In identifying the potentially irrigable land, Land suitable elements likesoilproperties (Depth, texture, and drainage),Considerations included slope, land usage, land cover, and distance to water supply. AHP was used to drive the weight of each influential factor, while all the above physical suitable area determination factors were weighted together using weighted overlay in Arc Gis 10.4 software indicated 19.26km2(0.29%)highly suitable, 698.53km2(10.4%)moderately suitable(S2), 4347.12km2(64.5%) marginally suitable(S3) areas for spate irrigation development. Finally,it is concluded that with some modification and management of moderately (S2) and marginally suitable (S3), 5064.91 km2 (75.19%) of the Waltane watershed's land was appropriate for the development of spate irrigation.