Hydrogeochemistry and isotopy of the groundwater intensely used in eastern Haouz and the area of Tassaout Upstream, Morocco.

English Abstract:

The Eastern Haouz and the Tassaout upstream area aquifer is the most stressed aquifer in the drinking water supply of cities, industrial processing and agricultural activity (more than 1000 wells and boreholes). This is an area where the demand for water is increasing year by year. Water levels measured in the study area shows a deep groundwater aquifer in the South and shallow in the North. The reservoir of the unconfined aquifer is characterized by a varying hydrodynamic parameters; the transmissivity varies between 1.10^-4 to 3,6.10^-2 m²/ s, and the storage coefficient is 2 to 10%. The piezometric map shows two areas of groundwater recharge; South from the High Atlas mountains and North from the Jebilets hills, two flows to the South West and the other to the North East.

A great variation is between the minimum and maximum values of the different ions, that variation is observed also in values of electrical conductivity, which varies between 761 and 7680 µS / cm, with an average of 2350 µS / cm. The analysis of several diagrams shows that there is a dominance of Na-Cl and Na-HCO3 facies with respectively a percentage of 48% and 12%. Groundwater of alluvial formations, surface water and also the water source have a slight dominance of Na-Cl, while the water circulating in the shales and Triassic formations show a high dominance of Na and Cl. Water samples from shale and Triassic formations are relatively mineralized and unfit for human consumption and for agricultural purposes. Groundwater in the central part circulating in the alluvium show low mineralization due to high power along the Tassaout River and infiltration of irrigation water from the water dam used to irrigate the agricultural area of the Tassaout upstream. Apart from salinity, about 25% of samples had nitrate concentrations above the allowable limits by WHO.

Measurements of stable isotopes show that the recharge of groundwater is controlled by local conditions that are feeding the unconfined aquifer by anastomosis in contact with limestone formations of the High Atlas and infiltration of the water dam used for the irrigation. The correlation between isotopic data and electrical conductivity has to distinguish isotopic differentiation characterized by three groups with a dominance of waters with the content of medium values of δ18O and electrical conductivities.