Effect of floods and management of pollution sources on temporal and spatial variations in water salinity of Karun River (Mollasani to Farsiat)

Rivers in addition to their environmental importance play a critical role in their neighboring people's lives. Karun River recognized as the most watery and longest river of Iran, in recent years, to declining flows and increasing the loading pollution sources to the river, its salinity has been increased. In this study, temporal and spatial changes in water salinity in the range of 105 km of Karun River from Mollasani to Farsiat were simulated using MIKE11 models. After calibration and validation of hydrodynamic and advection-dispersion model, numerical simulation results showed that in the effect of the loading of pollutants sources, salinity longitudinal profileespecially at the reaches of 60 and 90 km respectively positioned Ahvaz city and farmlands has increased as stepped. Maximum and minimum salinity changes take respectively place at the months of Aug. and Mar. To describe the rate of salinity variation in wetting and drying seasons, a fourth-order equation respectively with coefficient of determination of 0.99 and 0.98 was proposed. Results revealed that increasing flood discharge would lead to a significant decrease in the salinity of the river. In the month of Aug., removal of agricultural sources and in Mar., the removal of industrial and urban sources, have greatly influenced river salinity reduction at the upstream and downstream of Ahvaz, respectively. Results of this study can be used to study the effect of flow variation and pollution sources loading on the Karun River salinity and appropriate management solution provision.