Study of Groundwater-river Interactions Using Hydrochemical Tracers in Fissured Rock: Case of the Lobo Watershed at Nibéhibé (Central-West, Côte d’Ivoire)

Abstract

Water is a vital resource for all populations. However, there are warning signs that the water from the Lobo River used by SODECI to supply drinking water to the population is declining in quantity during the dry season and its quality is becoming poor due to climate variability and anthropogenic activities. However, the river is able to maintain a certain flow, probably with the contribution of groundwater. It is therefore a question of whether there is really a connection between surface water and groundwater. The aim of this study is to characterize the groundwater-river interactions based on the physico-chemical parameters of the Lobo watershed in Nibéhibé. The approach adopted is a coupled statistical-geochemical approach applied on data from two sampling campaigns (dry and rainy season). This coupled approach consisted, on the one hand, in understanding the chemical specificities within the water classes using the piper diagram and, on the other hand, in classifying the waters according to their physico-chemical similarity and highlighting the phenomena at the origin of the water mineralization using the Kohonen self-organized map (SOM). The results obtained from the piper diagram show that in both the wet and dry seasons, the chemical signature of the waters remains controlled by two main hydrochemical facies: the chlorinated calcium-magnesium nitrate hydrofacies and the bicarbonate calcium-magnesium hydrofacies. Kohonen's self-organized map has established that the mineralization of groundwater, under natural conditions, comes from the nature of the rocks crossed during infiltration and from the contact time between water and minerals. This work provides managers with decision-support tools for planning and searching for groundwater in support of surface water to reinforce the drinking water supply of the populations in this watershed.