Abstract:
Water resource project planning and implementation are affected by many parameters.
Among those parameters land use and land cover change has been one of a factor that alter
the hydrologic response of the watersheds leading to influencing stream flow and sediment
yield changes. The purpose of this study was to evaluate the impact of the land cover changes
on stream inflow and sediment yield to the reservoir in Gidabo watershed, Ethiopia using
Soil and Water Assessment Tool (SWAT). Land use map of 1986, 1994 and 2008 were used
for analysis. The simulation was done by dividing the watershed into 43 sub watershed and
by assigning a hydrological response unit based on multiple HRU definition. The model
calibration for stream flow and sediment was carried out using time serial data from 01
January 1995 to 31 December 2000 and a validation period from 01 January 2001 to 31
December 2003. The result of land use and land cover analysis has showed that the cultivated
land has mostly expanded, while forest, grassland and shrub lands were decreased during the
study period of 1986 - 2008. The result of sensitivity analysis showed that the stream flow is
highly sensitive to soil evaporation compensation factor (Esco) and sediment is most
sensitive to USLE support practice factor (Usle_P).
The calibration results for both stream flow and sediment yield showed good match between
measured and simulated data with the coefficient of determination of 0.86 and 0.83, Nash
Sutcliffe efficiency of 0.85 and 0.77 and percentage bias of -3.94% and -4.30% respectively.
And the result for validation for both stream flow and sediment showed good result with
Coefficient of determination of 0.83 and 0.82, Nash-Sutcliffe efficiency of 0.81 and 0.79 and
percentage bias of 3.15 and 0.57%. The evaluation of the model indicates that mean annual
stream inflow was increased by 20.14% between 1986 to 2008 LULC. Similarly mean annual
sediment yield was increased by 6.78t/ha between 1986 to 2008 LULC.
