Modelling Hydrological Response To Land Use Land Cover Change And Developing Best Management Practices In The Gidabo Watershed

Abstract

Due to the increase in population and socio-economic development, land use land cover (LULC) change is a very important issue considering global dynamics and their responses to water resources. Water resources that can be used for agricultural production, domestic use, and hydropower generation have persistently been affected by both temporal and spatial changes of LULC. However, quantifying the impact of LULC on water resources and developing best management practices (BMPs) is very important for the sustainable use of these resources. The broad objective of this study was to investigate the potential impacts of LULC change on hydrological responses and developing the BMPs that have been paramount to alleviate sedimentation in the study area of the Gidabo watershed in the Rift Valley Lake basin. The LULC change analyses for three periods (1990, 2005, and 2019) were performed using ERDAS Imagine 2014 with a maximum likelihood classifier. The result has shown, the expansion of agricultural land by 8.9% and reduction of forest land and shrubland by 7.11% and 7.53% respectively during the study period. In this study, the Soil and Water Assessment Tool (SWAT) model was used to examine the effects of LULC change on streamflow and sediment yield. The model performance in simulating streamflow and sediment yield was evaluated through sensitivity analysis, calibration, and validation processes. Statistical model performance indicators namely coefficient of determination (R2), Nash-Sutcliff efficiency (NSE), and percentage bias (PBIAS) were used, and the results indicates a good agreements between simulated and observed values during calibration and validation periods at three stations. Due to LULC changes, changes in streamflow and sediment yield were observed. Accordingly, average annual streamflow was increased by 1.16m3/s (2.13%) and 2.04 m3/s (3.62%), and average annual sediment yield was increased up to 3.45 t/ha/yr (44%) and 7.06 t/ha/yr (47.38%) for the period 1990-2005 and 2005-2019 respectively. Based on the average annual simulated sediment yield using 2019 LULC, the 10 critical sub watersheds whose annual sediment yield limit ranges above the tolerable limit were identified and prioritized for effective watershed management. Hence, three BMPs namely filter strips, terracing and reforestation were developed for critical sub-watersheds to reduce the sediment yield delivered to the Gidabo dam reservoir. The result revealed the terracing management option reduce the sediment yield up to 64.02%. Implementing filter strips with 5m, 3 m, and 1 m wide indicates 59.12%, 55.97%, and 50.73% reduction respectively whereas, reforestation has given the least reduction that is 40.98%. Therefore, applying terracing in critical sub-basins is the most effective practice for reducing sediment yield in Gidabo watershed.