Abstract:
This study was conducted to estimate temporal and spatial groundwater recharge
distribution of Weleh river catchment by using the WetSpass model. Meteorological data
were collected from stations, which were selected based on proximity to the catchment
and data availability. The catchment is covered by bare land (47.3%), agricultural land
(28.6%), shrub (15.8%) and forest (7%). Geologically, different formations are found
within the catchment the dominant ones are volcanic rock and sedimentary rocks. In this
study, long-term seasonal and annual groundwater recharge, actual evapotranspiration,
interception and surface runoff have been estimated by using the WetSpass model. In
order to run the WetSpass model hydro-meteorological data and biophysical data were
adjusted following the model requirement. The average annual long-term groundwater
recharge is estimated to be 46 mm/year (7% from annual rainfall) of which 40 mm occurs
during wet and 6 mm occurs during dry seasons. About 394mm of water is lost through
evapotranspiration from the catchment. 72% of the total annual evapotranspiration is lost
during the summer season while the rest 28% is released in the winter season. Actual
Evapotranspiration is the largest component of the water budget in Weleh catchment
constituting 61% of annual precipitation. WetSpass model also simulated the annual
runoff of the catchment and it gives 179 mm/year, which represents 27.5% of the total
annual precipitations of the catchment. From the annual surface runoff, 92% of the
surface runoff occurs during the wet months while the remaining 8% occurs during the
dry months. The annual interception rate of the catchment is 30 mm/year, which is 4.5%
of annual precipitation. 85% of the interception rate (25 mm/year) is intercepted at
summer season and the remaining 15% (5mm/year) occurs in the winter season. All the
four water balance components showed high spatial and seasonal variation. Generally,
Weleh river catchment has been manifested by high surface runoff and
evapotranspiration whereas seasonal and annual recharge amount is very low.