Assessing Water Quality Status Using a Mathematical Simulation Model of El Abid River (Morocco)

In semi-arid or arid regions, where available freshwater is limited, surface water requires repeated quality testing to avoid pollution. Sampling trips of different frequencies are onerous and require expensive laboratory analysis. Simulation appears to be a reliable alternative method to overcome such challenges. The simulation presented here was conducted by solving the mass balance equation while considering the inputs controlling each simulated parameter. The mass balance equation (a differential equation) was solved by finite difference numerical approximation to provide parameters for pollutant concentrations at each station or moment (based on selected steps). This solution was integrated to simulate pollution indicators (biochemical oxygen demand and dissolved oxygen), nitrogen forms, and orthophosphates. The National Sanitation Foundation water quality index (NSF-WQI) was calculated using these parameters. Using 12 months of measurement data, results were compared for NSF-WQI calculated through measured and simulated data, showing a significant correlation with R2 = 0.8, meaning the model demonstrated good calibration and validation. The elaborated model is a useful tool for decision makers to test and propose quality improvement solutions for watercourses suffering from quality deterioration.