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.

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Human activities and climate change are currently dominant processes that affect hydrological processes, resulting in alterations in water and sediment flows. Evaluation of the settling velocity of suspended solids is a critical parameter in modelling sediment transport. In this study, we investigated seasonal changes in suspended solids’ settling velocity and trapping capacity in the presence and absence of water turbulence on a dam reservoir. Using key parameters such as flow rate, mean settling velocity (V¯), critical velocity (vc), suspended solids concentration, ratio V¯/vc, and shape parameter ‘r’, the trapping capacity on the dam reservoir on the Lobo River in a tropical region was estimated. The results show that, considering the settling velocity of suspended solids, following the Gamma distribution law remains an innovative solution proposed to evaluate the trapping capacity in water reservoirs. The results show that the mean suspended solids settling velocity V¯ is well above the median rate V50%. For a parameter V¯/vc ≥ 4, there is an increase in the trapping capacity of the water retention. As established, a large proportion of the sediment is trapped. Furthermore, for a parameter V¯/vc ≤ 4, a decrease in the trapping capacity of the Lobo River water reservoir is observed.