Abstract:
Ethiopia’s primary water resources management challenges are due the extreme hydrological
variability and seasonality and the international nature of its most significant surface water resources.
The main objective of this study was to assess the impact of the Land use land cover changes on the
stream flow and sediment yield of the Gojeb watershed, which is located in the Omo Gibe basin.
The Soil and Water Assessment Tool (SWAT) is a watershed-based, semi-distributed hydrologic
model for simulating hydrological processes at different spatial temporal scales. The land use land
cover change analyses were performed using ERDAS Imagine 2014 which was used for further
analysis of SWAT. Land use land cover changes for three different years of 1989, 2000 and 2013
land use scenarios with different management practices were used for estimation of stream flow and
sediment yield. During the study period most parts of the Forest land were changed to cultivated
land. An increase of cultivated land by 14.97% over 30 years period (1985 – 2015) resulted an
increase of stream flow and sediment yield by 8.6 m3/s and 41.07t/km2 respectively. The Nash
Sutcliff efficiency, coefficient of determination (R2) and PBIAS to the measured deviation of
measured data (RSR) were used for evaluating the model performance. The model results has
showed a good agreement and correlation with the observed data with NSE > 0.75, R2 > 0.81, and
PBIAS < 0.07 values. Spatial variability of sediment done using the validated sediment yield results
of 2013 land use showed high potential source areas were found at upstream, high elevation and
slope lands. Hence, for the critical sub- watersheds the design and development of best management
practices were performed. Three BMPs (best sediment management scenarios) S1 (filter strip), S2
(stone bund) and S3 (reforestation) were considered in this study. The results has showed a decrease
of sedimentation by 22.9%, 29.4% and 32.3% sediment yield reductions implementing S1, S2 and
S3 respectively. Therefore practicing S3 for Gojeb watershed should be developed and encouraged
for efficient sediment reductions
