Study of Self-Purification Capacity in the Semi-Arid Zones: Case of Wadi Cheliff, (Northern Algeria)

Abstract

The aim of this paper was to study and predict the self-purification capacity of wadi Cheliff (in the section Oum Drou –Chlef). This was done primarily by measuring the Dissolved Oxygen (DO) downstream of a pre-selected pollution discharge point on wadi Cheliff and then predicting the same using the modified Streeter-Phelps equations. Twelve sampling stations are chosen, on a section of approximately 8.5 km of the wadi Cheliff (Oum Drou Chlef), to collect data with knowing the Biochemical Oxygen Demand (BOD), pH, stream velocity, stream depth and distance. Predicted DO deficit trend lines were first fitted by retaining the original re-aeration coefficient component, k2, of the modified Streeter-Phelps equation (United States Geological Survey equation) and subsequently by substituting it with our reaeration coefficient model. It was found that the latter displayed better predictive capacity. Results also demonstrated that the self-purification capacity of the river which is already limited by the relatively low DO saturation level is further threatened by the wastes being discharged into it at varying intervals. Some of these wastes are non-biodegradable which slows down the self-purification processes of the wadi. To preserve the underground layers of the area and to ensure a water of good quality for the irrigation, the Wadi Cheliff must be, necessarily, to protect from any pollution. key words: Surface Water Quality, Pollution, Dissolved Oxygen, reaeration coefficient,Wadi Cheliff.