Impact of Land Use/Land Cover Change on Reservoir Sedimentation: The Case of Ribb Dam Reservoir, Lake Tana Sub Basin, Ethiopia

Abstract

The land and water resources of the Lake Tana Sub Basin basin is in danger due to soil erosion, sediment transport, land degradation and storage capacity reduction. There is a need for sediment transport research of this basin that can improve catchment’s management programs.

This study assesses the impact of land use and land cover change effects on reservoir sedimentation using SWAT model in Upper Ribb watershed. The land use and land cover change analyses for three different years of 1973, 1995 and 2016 were performed using ERDAS Imagine 2014 which was in turn used for estimation of sediment yield. In this study the bush/shrub land were changed to grazing and cultivated land. An increase of cultivated land by 29.947% over 43 years (1973 – 2016) period resulted in an increase of sediment yield by 343.25 t/km²/year respectively. Model calibration and validation for sediment yield were done at Abo Bahir. The performance of the model was also checked at this station. Both the  monthly calibration and  validation  results  showed  good  match between  measured  and  simulated  sediment yield data  with  the  coefficient  of determination  (R²)  of  0.857, Nash-Sutcliffe  efficiency  (NSE)  0.832  for  the calibration,  and  R² of 0.834  and NSE  of 0.796 of  the  validation  period.

Spatial sediment distribution was done using the calibrated and validated sediment yield results of 2016 land use. High potential source areas were found at north-eastern part of the watershed which was a combined result of highly cultivated land, steep slope and erosive soil (Eutric Leptosols). Therefore, these critical sub- watersheds should preserve from further exposing of soil erosion through either forest resource development or uncultivated the steeply slope areas. And also the increasing/expanding bushes/shrub land should also be encouraged in the watershed first by applying for those most erosion prone sub watersheds.

Keywords: Upper Ribb watershed, SWAT, sediment yield, spatial sediment distribution.

DOI: 10.7176/CER/12-5-01

Publication date:May 31^st 2020