Abstract
Determination of groundwater recharge is a major challenge in areas where rainfall is generally abundant. Variability and uncertainty are inherent in the estimation of recharge, and several methods are therefore recommended for its estimation at a regional level. In this study, we evaluated several methods for estimating recharge: the web GIS-based automated hydrological analysis tool (WHAT), water table fluctuation (WTF), hydrograph analyses, a recession curve displacement method, graphical separation, and empirical formulas. The annual recharge estimated by combining direct recharge and base-flow varied from 84 mm in 2019 to 66.4 mm in 2020. The mean direct recharge was about 44 mm in 2018 and 57.3 mm in 2019, representing about 4% and 5% of the respective rainfall. In 2020, this direct recharge was 43 mm, or about 6% of rainfall, around 25% lower than in 2019. Base-flow separation methods and recession curve displacement generally gave low results, whereas modified empirical formulas gave results close to those of the WTF method and were considered more consistent and reasonable. The regression curve displacement method implemented in the United States geologic survey (USGS) RORA program was found to be unsuitable for the study area. However, the other methods presented more reasonable results and could be used to estimate groundwater recharge in the study area.
Highlights
Climate change and population growth are putting considerable pressure on the water resources of the Lobo catchment area, which are mainly used to supply drinking water to the population of the city of Daloa
Direct recharge was estimated by the water table fluctuation (WTF) method and em6piorfic1a8l methods, and later, by combining the direct recharge estimated by the WTF method and the base-flow estimated by the web GIS-based automated hydrological analysis tool (WHAT) method, the annual recharge was estimated (Figure 5)
The recession curve displacement method and flow data from the gauging stations of Sikaboutou and Nibéhibé were used to estimate the groundwater recharge in our study area
Summary
Climate change and population growth are putting considerable pressure on the water resources of the Lobo catchment area, which are mainly used to supply drinking water to the population of the city of Daloa. Located in the central-western region, Daloa is the third-largest city in Cote d’Ivoire and forms an economic hub for all localities in the Lobo catchment. The city and its surroundings are supplied with drinking water from the Lobo reservoir. This resource is crucial for these localities but is currently threatened by overexploitation and siltation [1] and is highly eutrophic due to multiple sources of pollution. Predicting the duration of possible exploitation and the flow associated with it requires an assessment of the renewal of the resource, i.e., the recharge
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