Groundwater Recharge Estimation Using Gis Based Wetspass Model. A Case of Jewha Watershed, Middle Awash River Basin, Ethiopia
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Date
2020-06
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Addis Ababa University
Abstract
Understanding the hydrological environment and groundwater availability leads to plan,
design, develop and manage the available water resources effectively. There are different
physical and empirical models to understand the water balance components of a given
watershed. One of the spatially distributed physical models is WetSpass model. The
WetSpass-M model has been simulated the seasonal and annual water balance components
of Jewha watershed successfully. Based on the model, the annual ground water recharge in
Jewha watershed is 0 and 404mm as a minimum and maximum value with a mean of
124mm, which is represent 15% of the total annual rainfall. This mean annual groundwater
recharge is equivalent to 67,450,240m3
/year. 87% (107.7mm) of the recharge is occurred
in summer (Jun to September) and the rest 13% (16.5mm) of recharge percolate in winter
(October to May).The model result also shows that the annual value of runoff in Jewha
watershed is vary in range from 79.75mm to 831.5mm as a minimum and maximum value
respectively, with a mean of 299.5mm. The mean value accounts about 35% of the total
annual rainfall of the watershed. The annual evapotranspiration from the watershed is
simulated as a minimum and maximum value of 277.9mm and 2857mm with the mean
value of 436mm respectively, and the standard deviation is 211.8. About 71% of the total
annual evapotranspiration is lost during rainy season and the remaining 29% is released in
dry season.
The sensitivity analysis of the different input variables was conducted and most of the
variables are highly sensitive in Jewha watershed. The results of the analysis show that
rainfall, potential evapotranspiration and slope are the most important hydrologic process
in the study area in terms of affecting the amount and rate of the different water balance
components. The parametric coefficient of alfa coefficients, interception coefficients and
Lp coefficient also relatively sensitive. The calibration was made between the simulated
and observed water balance component value of the watershed. The calibration process has
been performed through coefficient of determination(R2
) and the Nash- Shuttle efficiency
(NSE). The result shows that, the observed and simulated value is in good fit by R2
of 0.91
and NSE of 0.74.
Description
Keywords
Jewha watershed, Recharge, Runoff, WetSpass model, Water balance