Abstract:
Birr watershed is found 60 km south-west of Bahirdar at the non-asphalted road
connecting Bahirdar to FersBet town, Degadamot woreda. The effects of land use and
land cover change have an impact on sediment yield on the Birr watershed. The study
mainly focuses on impact of land use and cover change on sediment yield and stream
flow under different land use and land cover change of the sub basin. Other effects on the
sub basin, like water balance, ground water changes, and climate change impact would
not be covered in the study. Three hypothetically land use land cover change scenarios
were developed. A physically based, spatially distributed hydrological model, SWAT
would be used to simulate LULC effects in the hydrological response (sediment and
stream flow) of Birr sub basin. Intensively cultivation land use increased in the
watershed whereas moderately cultivation land use decreased. The performance of the
SWAT model was evaluated through sensitivity analysis, calibration and validation. Both
the calibration and validation result shows good agreement between observed and
simulated stream flow R
2=0.83, NSE=0.79 and R2 =0.76, NSE=0.74 respectively and
sediment yield R
2=0.77, NSE= 0.73 and R2=0.72, NSE=0.07 respectively. The model was
capable of simulating stream flow and sediment yield for Birr watershed. But the result
from sediment simulation was not good performance in the validation period. This is
inability of SWAT model simulate gully erosion and land slide. Sensitivity analysis using
SWAT model has pointed out that some crucial parameters control the stream flow and
sediment yield in the catchment. Soil erosion is not solely driven by rill and sheet erosion.
Sever sediment yield and stream flow was observed on dominantly cultivated areas in the
watershed. The results could have been improved by using longer period of sediment
recorded and better quality land use and soil data.
