Groundwater Recharge Estimation Using WetSpass Modeling in Upper Bilate Catchment, Southern Ethiopia

Abstract

The study area, upper Bilate catchment, is strongly dependent on groundwater like other rural catchments in the country. The main objective of this work is to quantify the amount of groundwater recharge in upper Bilate catchment. Recharge was estimated using physically based distributed recharge model called WetSpass. As input to the model precipitation, potential evapotranspiration, temperature and wind speed were estimated using data collected from meteorological stations located within the catchment and nearby areas. The physical environmental data including land use, soil type, and groundwater depth were collected from field and existing maps. Slope and topography map were generated from Shuttle Radar Topographic Mission elevation data. Using the model the mean annual recharge of the catchment was found to be 9.4 % of the precipitation whereas the direct runoff was found to be 20 % of the precipitation. The study area is characterized by lower groundwater recharge relative to surface runoff due to the effect of impermeable soils, morphology of the land and land use/land cover of the study area. The western and northern parts of the area are identified as recharging zone and the central and southern part are discharge zone. The groundwater recharge zoning map was validated using base flow separation method and also compared with previous groundwater recharge works of the study area. This study revealed that the groundwater recharge estimation using WetSpass model is reasonable and useful for quantification of annual groundwater recharge with spatial and seasonal variation and also capable in the identification of groundwater recharge zones in the area under study.

Drought propagation in the hydrological cycle in a semiarid region: a case study in the Bilate catchment, Ethiopia

“…12) shows that the calculated groundwater recharge ranges from 0 to 37 mm/month with a spatial average of 10.10 mm/month. This result is 9.8% of the monthly average rainfall of the study area and this estimated groundwater recharge confirms the findings of Dereje and Nedaw (2019) for upper Bilate catchment, showing that the average groundwater recharge is 9.4% of the annual precipitation. The influence of rainfall distribution in the catchment is significantly noticeable in the spatial distribution of groundwater recharge.…”

Untitled

“…In the Birki Watershed, Eastern Tigray, Northern Ethiopia, [30] get 85.5 percent of yearly precipitation. [31] simulated 69.8% of annual precipitation in the Upper Bilate Catchment, Southern Ethiopia, and [26] reported 81 percent in the Illala Catchment, Northern Ethiopia. As a result, evapotranspiration eliminates the bulk of annual precipitation [32,33].…”

Exemplifying the Effects Using WetSpass Model Depicting the Landscape Modifications on Long‐Term Surface and Subsurface Hydrological Water Balance in Bilate Basin, Ethiopia

“…erefore, the study concluded that precipitation and LULC are the main driving factors of actual evapotranspiration in the basin. e previous investigation conducted by Dereje and Nedaw [14] and Molla et al [73] have estimated groundwater recharge, EVT, and surface runoff using the WetSpass hydrological model in upper Bilate watershed and Abaya-Chamo basin.…”

“…A few researchers [74] have revealed that the settlement and built-up areas have a tendency to generate a high volume of surface runoff within the region because they have substantially smaller amount vegetative area. erefore, the study conducted by Dereje and Nedaw [14], and Molla et al [73] have been ignored by the potential contributions of settlement and built-up area on hydrological processes during their evaluation, although the dynamics of urbanization is evidently ongoing in the basin. During the study, the potential impacts of settlement and the built-up area on surface and subsurface water were investigated, and the determined results experienced that surface runoff has been evidently affected by the degree of settlement and modification of urbanization in the Bilate basin.…”

“…In Bilate basin of Ethiopia, cultivated land and settlement area are impertinently increasing but simultaneously forest, shrub, and bushlands are declining [13]. In addition to this, the basin is characterized by low groundwater recharge relative to the surface runoff due to the effect of impermeable soils, the morphology of the land, and LULC [14]. Water balance describes tracking the equilibrium between flowing input/output the water of any hydrological system, and there exists various mechanisms for estimating magnitude and distribution of surface and subsurface water balance components which can be broadly classified into physical, chemical, tracer, and numerical modelling methods [15].…”