IMPACTS OF LAND USE LAND COVER CHANGE ON RESERVOIR SEDIMENTATION (THE CASE OF RIBB DAM, IN LAKE TANA SUB BASIN, ETHIOPIA)

Abstract

Land use land cover (LULC) change is the challenge and continuous drivers of environmental change. Understanding the rate and process of change is, therefore, basic for managing the water resources and the environment at large. This study was intended to analyze the LULC changes impacts on sediment load from 2000 to 2018 periods, and select critical (hot spot area) sub basins and recommend best management practice for Ribb watershed of Lake Tana sub basin, Ethiopia. Both climate and hydrometric (flow and sediment) data were collected and analyzed over the period 1990 to 2018. Two time satellite imageries of the Land sat product (2000 and 2018) were used for land use change detection. The hybrid classification technique for extracting thematic information from satellite images were employed by using ERDAS model for classification of LULC. The Soil and Water Assessment Tool (SWAT) model was calibrated and validated to estimate sediment load of the watershed during the period 1992 to 2001 and 2002 to 2007 respectively. To manage the sediment load best management practices (BMP) as a scenario (filter strip, grassed water way and contouring) were implemented on 2018 LU map. The land use change detection result indicate that cultivated land has expanded from 66.87% in 2000 to 75.53% in 2018. Between 2000 and 2018 periods, it was increased by 8.66 %. The rate of increment during 2000–2018 periods were 608.915 ha/year. Similarly, settlement area had also increased by 2.09% from 2000–2018 periods. Similarly, shrub land and bare land also decreased at a rate of 412.868 and 227.651 ha/year, respectively, between 2000 and 2018 periods. Also the water body decreased at a rate of 1.593 ha/year between 2000 and 2018. The SWAT model result depict that the model give reasonable fit of sediment flux with observation during calibration and validation as evaluated with ENS ( 0.63 ) , R2 ( 0.67) and percent bias (17%) during calibration and ENS ( 0.58) , R2 ( 0.71) and percent bias of (12%) during validation period. Moreover, the severity of soil loss rate was increased with the average of 26.89 ton/ha/year from 2000 to 2018 LULC, which indicates that the management practice, was weak within the watershed. The BMP scenarios depict that filter strip was significant amount of LULC conversions practice and soil loss rate had occurred in the watershed from 2000 to 2018 periods, and expected to continue in the future. Thus, appropriate conservation and management practice are very much crucial to safe guard the life of the reservoir