Groundwater Quality for Irrigation Purposes in the Diass Horst System in Senegal

Due to surface water scarcity and variability in rainwater events in the Thies region, Senegal, farmers mostly rely on groundwater resources to improve yield production, although water quality in the hydrosystem and its suitability may be an issue. The objective of this study is to evaluate suitability of the Maastrichtian and Paleocene aquifers located the central western part of Senegal in the Thies region for irrigation purposes. For this purpose, chemical analyses were carried out on the major ions on the Maastrichtian and Paleocene aquifers through a network of 62 sample locations (39 from the Maastrichtian and 23 from the Paleocene) sampled in June 2019. Different water suitability assessment indices were used to evaluate the potential for irrigation, including sodium absorption ration (SAR), percentage of sodium (Na%), permeability index, Kelly ratio (RK), and salinity potential (SP) together with Wilcox and USSL diagrams as methods. The results indicate, that the Ca-Mg-HCO3 water type is dominant in the Maastrichtian aquifer, while in the Paleocene aquifer, HCO3-Ca-Mg and Cl-Ca-Mg are the main water types. The combination of these computed index values indicates that the percentage of suitable water for irrigation purposes accounts for 89.7% and 86.9% of the samples for the Maastrichtian and the Paleocene aquifers, respectively. On the other hand, water samples unsuitable for irrigation purposes range between only 10.3% and 13.1% for the two aquifers.