Impact of hydraulic and storage properties on river leakage estimates : A numerical groundwater flow model case study from southern Benin
Kpegli, Kodjo Apelete Raoul ; Zee, Sjoerd E.A.T.M. van der; Alassane, Abdoukarim ; Bier, George ; Boukari, Moussa ; Leijnse, Anton ; Louw, Perry G.B. de; Mama, Daouda - \ 2018
Journal of Hydrology: Regional Studies 19 (2018). - ISSN 2214-5818 - p. 136 - 163.
Benin - Discharge loss - Flow modelling - Groundwater recharge - Ouémé - River leakage
Study area: The coastal sedimentary basin including the Zou and Ouémé rivers in Benin. Study focus: River discharge loss is known to occur on the Zou and Ouémé rivers in southern Benin since a couple of decades ago. The reason behind this discharge reduction remained so far unclear. In this study, we focus on creating a 3D-numerical model of the system and on evaluating the sensitivity of leakage between the rivers and aquifers to various parameters. New hydrological insights for the region: Results show that leakages along the Zou river and Ouémé stream are tiny (i.e., ∼3% of the discharge losses). This implies that the observed water loss from the Zou and Ouémé rivers is not likely caused by the leakage (infiltration) along these rivers into the subsurface. The streambed conductance is found to be among the factors that impact less the computed leakages in the study area. This study has ranked the different hydraulic and storage properties in their order of importance with respect to the computation of river leakages along the concerned rivers. The determined rank of importance of the hydraulic and storage properties can guide river leakage modelling exercises in similar regions elsewhere.
Development of a conceptual groundwater flow model using a combined hydrogeological, hydrochemical and isotopic approach : A case study from southern Benin
Kpegli, Kodjo Apelete Raoul ; Alassane, Abdoukarim ; Zee, Sjoerd E.A.T.M. van der; Boukari, Moussa ; Mama, Daouda - \ 2018
Journal of Hydrology: Regional Studies 18 (2018). - ISSN 2214-5818 - p. 50 - 67.
Hydrochemistry - Isotope - Ouémé - Piezometry - Turonian-Coniacian aquifer
Study region: The Turonian-Coniacian aquifer system in the North of the Coastal Sedimentary Basin, southern Benin, West Africa. Study focus: The Turonian-Coniacian aquifer is the major aquifer in southern Benin and is the main source of water supply for the population. The pressure on groundwater resources from the Turonian-Coniacian aquifer is increasing since few artesian wells tapping into this aquifer already show decrease in their yields. Preventing extinction of the artesian outflows requires as a first step a thorough understanding of the groundwater flow system: groundwater recharge areas, downstream areas, and flow directions. In this study, a combined hydrogeological, hydrochemical and isotopic approach was applied to understand the groundwater flow within this aquifer and to develop a coherent conceptual groundwater flow model. New hydrological insights for the region: The piezometric results indicated three main groundwater flow directions. Stable isotopes results confirmed the piezometry as the most depleted and enriched values in Oxygen-18 and deuterium were found respectively in downstream areas (southern region) and in the recharge areas (northern region) indicated by the piezometry. Similarly, higher tritium contents (up to 3.5 Tritium Unit) characterize recharge areas and low tritium contents (<0.12 Tritium Unit) were found in downstream areas. The combination of these results with the geologic and topographic data led to a coherent conceptual groundwater flow model shown in this paper.