Investigating trends of qualitative changes of Neka River using the QUAL2Kw in the downstream of Gelevard Dam

Rivers, as one of the available surface water resources that are exposed to pollutant discharge have extra importance. In this study, while monitoring and simulating the process of qualitative changes in the 8 km reach of Neka River by using the QUAL2Kw, the effects of dams, natural flow waterfalls and bed stabilization structures were evaluated. For this purpose, twice qualitative sampling and local visits were performed. Then, the initial model was prepared and the estimation of data defects, the model was calibrated and validated. evaluation of trend changes in parameters showed that all parameters are within the standard reach and the river has a high self-purification capacity. trending of dissolved oxygen changes showed that the concentration of these parameters was close to saturation, which was due to the favorable hydraulic conditions of the river for aeration rate and the presence of numerous natural and artificial waterfalls in the river. Although the pH value was within an acceptable range, some sections were close to the saturation range because of the release of carbon dioxide due to waterfalls in the flowing water, which the model simulated these effects well. Also, the existence of small dams and creation of a wetland behind these dam Cause to bacteria have been given more time to decompose organic matter, which has increased the alkalinity and pH reach. The results analysis and error indicators showed that the QUAL2Kw model has a good accuracy in simulating the quality of Neka river.