Abstract:
Land use change is a very important issue considering global dynamics and their response on
hydrologic characteristics and soil and water management of an area. Significant land use
changes have observed in Tekeze dam watershed using 1986 and 2008 LULCs as a reference
time. The main objective of this study was to estimate the potential impacts the LULC dynamics
on hydrological response and prioritization of sub-watersheds according their sediment
potential. This was done by integrating SWAT model with GIS. The simulation and sensitivity
analysis for each land use was done by dividing the watershed in to 47 sub-watersheds and
assigning HRUs based on multiple HRU definition. Both automated and manual calibrations
were done using time series data 1978-1982 for 1986 LULC and 1996-2002 for 2008 LULC. The
model was validated using an independent time series data of 1983-1985 for 1986 LULC and
2003-2006 for 2008 LULC. After performance of the model was evaluated and become in its
recommended limit using statistical performance indicators, impact of LULC dynamics on
stream flow and sediment yield was evaluated using three scenarios (climate of 2000s & 2008
LULC, climate of 2000s & 1986 LULC and climate of 1980s & 1986 LULC) and sub watersheds
were prioritized using the first scenario. Significant change in response of the catchment stream
flow and sediment yield was obtained due to LULC dynamics. Accordingly, the mean annual
stream flow increased by 6.02% (129.20 to 137.74 m
3
/s) and the impact on sediment yield
amounts to an increase of 17.39% (12.54 to 15.18 ton/ha/yr). The first 13 sub-watersheds, whose
annual sediment yield limit ranges above the tolerable limit (18 ton/ha/year), were prioritized
according their sediment for watershed management efforts. The maximum sediment outflow of
these 13 sub watersheds ranges from18.49 to 32.57 ton/ha/year and are characterized
dominantly by cultivated land, shrub land, bare land & grass land with average land slope
ranging from 7.9 to15.2% and with dominant soil type of Eutric cambisols. Therefore these
results can help to formulate and implement effective, appropriate and sustainable watershed
management which in turn can help in sustaining the reservoir storage capacity of the dam.
