Analysis of ambo water supply source diversion weir sedimentation and assessing impact of land management practice through hydrological studies

Abstract

Huluka River diversion weir, which diverts water supply for Ambo town, has been under severe sedimentation. In this study, the ArcSWAT model was applied to determine the sediment yield and sediment load of the Ungauged Huluka River watershed through the parameters transfer method. This particular study calibrated and validated the ArcSWAT model on the Guder River gauging station of watershed area 659 km2. The calibrated and validated best values were extended to all the sub-basin to estimate the sediment yield and sediment load of the ungauged Huluka River watershed. The ArcSWAT model was found certain with statistical performance procedures like regression coefficient, Nash–Sutcliffe and percentage of bias. The model was calibrated and validated with accepted statistical performance values on the monthly time scale. The statistical performance like regression coefficient, Nash and percentage of biased were dramatically increased upon the validation period to very good range according to Arnold et al. The estimated average sediment yield of the whole Guder sub-basin was found to be 4.3 (ton/ha). The annual average sediment load contributed from the Huluka River watershed was found to be 37.5 Kiloton/year. The estimated average annual sediment quantities at Guder gauging station and the whole Guder sub-basin were 344.8 Kiloton/year and 1.1 Megaton/year, with data ranging from 1998 to 2014 (17 years). Three different best management practices (BMPs) such as contouring, strip cropping and terracing were evaluated to see their effectiveness on the whole sub-basin. The sediment yield reduction with these BMPs was ranged from 58 to 62% at Guder hydro-gauging station with simulation period of 1998–2014. The sediment yield was strongly decreased to 76% with these BMPs at the Upper Huluka watershed.