Quality assessment of surface and sediment pore waters and their behaviours using WQI index and geostatistics approaches. Case study: El Malleh dam reservoir, Morocco

The El Malleh dam reservoir is an important water source for irrigation and protection against flooding in the Mohammedia region of the kingdom of Morocco. However, flash floods threaten the sustainability of the reservoir by sedimentation and water quality contamination. Pollution sources could arise from sediment mobilization in the reservoir bottom, or carry by water flow from the watershed to the dam reservoir. The current study evaluates the surface and pore water quality, focuses on their behaviour based on the laboratory results, the Water Quality Index (WQI) and statistical analysis. The results show that the concentration of nutrients was not significant. The concentrations of major elements differ from surface waters to pore waters and from one parameter to another. For instance, the Cl concentration in the surface water ranged from 852 mg L-1 to 1065 mg L-1, and from 10 mg L-1 to 7810 mg L-1 for pore water. Besides that, the calculation of WQI indicated that the sediment pore water quality was unsuitable, and the surface waters quality was in a poor and very poor category.