Abstract
The coastal sedimentary basin in southern Benin consists of monoclinal layers divided into two plateau zones (North and South) which are separated by a longitudinal depression ESE-WNW. The valleys of the main N-S-oriented rivers (Ouémé, Couffo and Mono) set the bondaries of the different plateau of the BSC (Coastal Sedimentary Basin). The present study, based on geology, hydrochemistry, temperature and log data available on boreholes, makes a physico-chemical characterization of the waters of the gushing aquifers of the coastal sedimentary basin of Benin. The gushing water boreholes are shared between the valleys of the main rivers of the BSC. Some of these boreholes are thermal with a water temperature between 38 and 69 degrees Celsius. The hydrogeological correlations established in the BSC in accordance to the North- South direction in the valleys of the main streams (Couffo and Ouémé) reveal that the captured aquifers are sands, marls and limestones that respond either in major discordance (northern zone) or above the sedimentation gaps (southern zone). Chemical analyses have shown that gushing thermal waters are mineralized in the south with a neutral to basic pH and are highly concentrated with bicarbonate, calcium and magnesium ions. In the North, on the other hand, thermal waters are acidic with a pH ranging from 4.8 to 5.9. The acidic nature of the northern waters is influenced by the crystalline base while the southern neutral to basic waters are influenced by the lithological nature (limestone and marl) of the aquifer. The random distribution of thermal water boreholes in the valleys of the main BSC streams is believed to be related to tectonic events.
Highlights
Groundwater is a valuable asset for human consumption and other multiple uses; this is especially true when groundwater is thermal (IEA, 2011)
The coastal sedimentary basin in southern Benin consists of monoclinal layers divided into two plateau zones (North and South) which are separated by a longitudinal depression ESE-WNW
The gushing water boreholes are shared between the valleys of the main rivers of the BSC
Summary
Groundwater is a valuable asset for human consumption and other multiple uses; this is especially true when groundwater is thermal (IEA, 2011). They are accessible when they are gushing (Adissin et al, 2019). The permanent flow of these waters promotes their multiple uses for the development of small-scale agriculture (market gardening, irrigation) and livestock (Ahossi, 2020). As thermal water, they serve other purposes such as energy supply and sanitary treatment (Kapasa, 2014). Among the multitude of gushing water boreholes, one can notice an unexplained distribution of gushing and thermal water points to this day
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