Abstract:
Im pacts of land use land cover change on watershed runoff and sediment yield of the Keleta
watershed (1150Km
2
), Upper Awash sub-basin, were assessed using hydrological modeling. The
study utilized different types of data including DEM, soil map, Landsat TM and ETM satellite
data and the field observations. Two date Landsat image, 1986 and 2005, were used for
generating the land use/land cover map of the study area and to detect the changes between these
two time periods were simulated by the Soil and Water Assessment Tool (SWAT) model and
were compared with measured values. The six main land use changes were identified as an
increase of cultivatio n land from 52.5% to 68% and decrease of forest land 11.8% to 1.7 % of the
watershed area during the two decade period. Using the two generated land cover maps, two
SWAT models set up were run to evaluate the impacts the land use and cover changes o n
the stream flow of the study watershed. The performance of the SWAT model was evaluated
through sensitivity analysis, calibration, and validation. The most sense parameters were
identified to be sensitive for the runoff and sediment yield of the study area and used for model
calibration and validation. This study presents the calibration and validation of SWAT for the
runoff and sediment yield from 1995-2005 and 2006-2009 respectively. Based on this values for
Coefficient of determination (R²), Nash-Sutcliffe model efficiency (NSE), Root mean square
error standard deviation ratio (RSR) and percent bias (PBIAS) are found to be 0.82, 0.81, 0.44
and -9.29% in calibration and 0.83, 0.76, 0.49 and -7.92% in validation for flow analysis
respectively . Similarly, sediment model efficiency indicators R
2
, NSE, RSR and PBIAS 0.73,
0.69, 0.55 and -10.65% for calibration and 0.74, 0.62, 0.61 and 2.81% for validation
respectively. The average annual simulated runoff and sediment yield is 1424.24mm and
54.98t/ha in 1986 and for 2005 1557.33mm and 73.11t/ha respectively. Average annual
variability of sediment yield in each sub-watershed range from 0.06 to 13.83tha
-1
y
-1
in 1986,
whereas in 2005 the sub-watershed contribute from 0.26 to 17.86tha
-1
y
-1
of the sediment yield.
The built SWAT model can be utilized to simulate different scenarios to examine the effect of
different types of management practices and land use land cover.
