Modelling the surface water quality of the Agrioune River in the north-east of Algeria by the PEGASE model

In this study, the physicochemical parameters of the river streams of the Agrioune watershed were evaluated by experimental monitoring and surface water quality modelling. The PegOpera Software suite was used to apply the PEGASE model to the Agrioune River/Basin (north-east of Algeria). This model was used to simulate different parameters concentrations, its application on the Agrioune watershed case is one of the first works that are currently being carried out on the semi-arid regions. In addition to low flows, the surface river water quality in these regions is mostly influenced by urban discharges and agricultural activities. Seven parameters are predicted based on the existing distribution of point and diffuse pollution sources, they are compared to available measured values. A significant correlation was obtained between the simulated and the measured values after calibration of some model inputs. Model performance showed good statistical agreements with a Nash-Sutcliffe efficiency (NSe) oscillating between 0.44 and 0.89 and with determination coefficient (R 2 ) varying between 0.66 and 0.94 for the whole studied parameters. The simulation allowed to locate and to distinguish five different river water classes according to Seq-Eau model. Theses quality classes pointed out some river zones with unsatisfactory physicochemical status, and that have to be addressed with priority measures in order to improve their quality. Furthermore, the model was also used to simulate the impact of replacing settling basins by WWTP in the lower part of the Agrioune watershed. The results showed satisfactory reduction of some pollution parameters concentrations. The PEGASE model and the present study may be useful and may constitute a practical tool for managers to simulate several scenarios for improving the water quality in the Agrioune watershed.