Abstract:
Land use/land cover change has been responsible for altering the hydrologic response of
watersheds leading to impacting river flows. Various water resources projects planning and
implementation will require knowledge of the extent of these changes on watershed hydrology.
Soil erosion and land degradation is a serious problem in the Borkena watershed on
upper Awash sub basin. This is located in the south Wollo zone, North East part of Ethiopia in
Amhara Regional State. There was rapid growing population and also lack of awareness of the
effective watershed management and agricultural practices. The main objective of the study is to
assess the effect of land use/land cover change on runoff and soil erosion at Borkena River
watershed using soil and water assessment tool (SWAT) model. In this paper the effect of land
use changes on catchment’s hydrology is observed particularly on surface runoff. To carry out
this SWAT model 2012 was used for simulation. The delineated watershed was divides into 5 sub
basins and 51 HRUs by the model. Model calibration and validation was done at Kombolcha
flow gauge station. The semi-automated Sequential Uncertainty Fitting (SUFI2) calibration
process built in SWAT calibration and uncertainty program (SWAT-CUP) were used to calibrate
the model parameters using time series of flow data of 1982 to 1991 and validated with the
observed data from years 1992 to 2001. In addition to this the model efficiency was checked at
this station. Based on this values for coefficient of determination (R2
) and Nash–Sutcliffe
efficiency (NSE)were found to be in the acceptable range i.e.(R2=0.91,NSE=0.89) during flow
calibration and(R2=0.89,NSE=0.82) for validation period. The annual surface runoff 272.78mm,
lateral flow 241.63mm, total water yield 841.8mm ground water flow (shallow) 310.54mm and
sediment yield 165.71ton/ha at the study watershed was found from the existing land use map.
Then two scenarios were developed to observe the impact of land use changes. Based on this at
scenario1garss land changed to cultivation land has resulted in 6.41%, 15.96%, 9.62%, and
41.73% increase in surface runoff, lateral flow ,water yield and sediment yield respectively, but
decrease ground water by 0.68%. At scenario 2 grass land changed to plantation forest have
resulted in decrease by 1.3%, 8.4%, 5.5% for surface runoff, sediment yield respectively and
increase lateral flow, total water yield by 17.5%, 9.8% and ground water by12.5%.
