Spatial evolution of surface water qualte, Wadi Kebir Watershed (North-East Algeria)

Abstract

Wadi Kebir which represents the downstream part of the Kebir-Rhumel watershed, is characterized by a dense hydrographic network, a rainfall varies from more than 600mm/year in upstream (Beni Haroun dam) to more than 1000mm/year at the mouth of wadi Kebir (Ledjnah region). Its waters present a resource for drinking water supply (upstream part), as well as for agricultural development in the downstream plains. The objective of our research work is to determine the quality of the raw water of wadi Kebir and its tributaries. A total of ten samples were taken during the period of high water (April 2017): six samples on the tributaries of the wadi and four samples in the waters of wadi Kebir from upstream to downstream. The physico-chemical parameters of the - 2- - water (T, pH, EC) were measured in-situ, the major elements (Ca2+, Mg2+, Na+ , K+, HCO3 , SO4 , Cl ) and the + - - 3- indicators of pollution (NH4 , NO2 , NO3 , PO4 ) were analyzed at the Geological Engineering Laboratory (LGG). The results obtained show an organic pollution of the waters of Wadi Kebir and its tributaries with levels in the range of 0, 16 to 4, 72 mg/l in ammonium and 0.005 to 3, 67 mg/l in nitrite. The electrical conductivity varies from 1306 to 3460 s/cm indicating charged water. However, it remains below 1080 s/cm for the tributaries. The surface waters of the Wadi Kebir watershed are more or less alkaline (8, 19 - 8, 67). The most dominant hydrochemical facies is bicarbonate calcic-magnesian with minor hydrochemical facies such as sulfate-sodic- magnesian. Its chemistry is controlled by the weathering of the geological formations that characterize the watershed. The Organic Pollution Index (OPI) revealed a degradation of the water quality from upstream to downstream, especially after the passage of the wadis through the different agglomerations such as those of Elmilia and Djamaa.