Abstract:
Biji catchment has experienced in land cover change during the last fortieth years due to
human disturbance, so it’s important to understand the impacts of land cover change to the
groundwater recharge to sustain the balance between recharge and discharge of the area.
The main objective of this study is to evaluate groundwater recharge and its response to land
use land cover change in Biji catchment using spatially distributed water balance model
(WetSpass). Thirty three years’ of average hydro-meteorological and biophysical catchment
characteristics has been prepared in the form of digital maps (grid format).
In Biji catchment four land use / land cover classes were defined during the study: Bare land,
Agricultural areas, Builtup areas and shrub land. Land cover change detection analysis from
1986 to 2019 has shown an increment in the proportional of the Agricultural land from 16.8%
to 24.78%, bare land from 15.8% to 14.9%, shrub land from 67.3% to 59.7%. While built up
areas increased from 0.06% to 0.5%.
In 2019 Results of the model show that 61.1% of the precipitation in the catchment is lost
through evapotranspiration, 34.2% recharges the groundwater system and only 4.7% becomes
surface runoff. Also annual estimate for long term average annual groundwater recharge with
respect to land use land cover change in 1986, 2005 and 2019 was estimated as 135.84, 142.49,
137.72 mm respectively. In addition, the model indicated the spatial variation of components
with different land cover and soil texture combinations. Surface runoff and groundwater
recharge are more sensitive to soil textural classes while actual evapotranspiration varies well
with land use type.
The model was calibrated and validated using historical flow data from the 1980 to 1987 and
validate from 1988 to 1991 respectively. The R2 and Nash- Sutcliffe Efficient (NSE) value for
the watershed were 0.82 and 0.8 for calibration and 0.88 and 0.84 for the validation
respectively. It has been concluded that LULC change affect the water balance ofbiji catchment especially groundwater recharge
