Étude de la qualité des ressources en eau destinées à la consommation humaine dans les sous-bassins versants du secteur aval du barrage de Lagdo (Régions du Nord et de l’Adamaoua-Cameroun)

Abstract

Beyond the lack of sanitation and access to drinking water, water quality is a public health determinant whose monitoring and evaluation could significantly reduce the mortality rate of populations in general, those in rural areas, particularly children under five. However, heavy rain in 2012 and 2014 caused water to overflow into the Lagdo Dam reservoir, leading to severe flooding. These floods caused severe damage to the lives of populations downstream and constituted a health challenge. Thus, this thesis focused on studying the quality of water resources in sub-watersheds downstream from the Lagdo Dam, to identify the main causes of waterborne diseases. Between late September and early October 2017 (rainy season), a period of resurgence of waterborne diseases, 40 and 34 water samples were collected respectively in the North Region (R-NO) and in the Adamawa Region from water source including boreholes (BH), protected wells (PW), unprotected wells (UW) and surface water (SW). From samples, six bacteriological and twenty physico-chemical parameters were analysed. The collected data were evaluated by statistical methods, calculation of Water Quality indices (WQIs), and hydrochemical methods. The results revealed a statistically similar state of water between the regions (Mann-Whitney U test, p ˃ 0.05) regarding their bacterial content, which did not meet the standards. The stratification of water samples by types of water sources revealed that BH was more polluted in the R-NO while BH and UW were more polluted in the R-AD, and also led to the underlying causes of waterborne diseases. The assessment by calculation of the National Sanitation Foundation Water Quality Index (NSF-WQI) classified 63% (R-NO) and 97% (R-AD) of the waters in the "poor quality" category, indicative of the immediate causes of waterborne diseases. The PCA/FA combination revealed the sources of water pollution. The HCA classified low, moderate, and highly polluted waters in the R-NO; and unpolluted, low and moderately polluted waters in the R-AD. The hydrochemical results revealed the scaling nature of most waters; a Mg-Ca-HCO3 facies for 85% (R-NO) and 79% (R-AD) of the water samples; and a chemical composition mainly controlled by silicate dissolution, reverse cation exchange, and calcite precipitation. The results of the present study reveal that during the rainy season, groundwater in the R-AD was mainly affected by diffuse pollution, whereas in the R-NO it was point and diffuse pollution. This should be the goal of policymakers when planning and implementing measures to protect drinking water sources, human health and reduce water treatment costs.