Water Quality Zonation of Beshar River in Yasuj City

This study was conducted to monitor the current water quality of Beshar River by the Iranian Surface Water Quality Index (IRWQIsc). Monitoring of the river water quality was done based on sampling 12 stations along the river in October of 2021 as the period of water shortage and January of 2022 as the period of high water flow simultaneously with sampling two other stations (fish farm effluent and Yasuj wastewater treatment plant effluent) as the point source pollution entries. The results of zoning Beshar River based on IRWQIsc in the period of water scarcity showed a decrease in river water quality from the upstream to the downstream part. 41.66% of the upstream part of the river (Tang-e Tizab to Dehno) was in a relatively good condition, 8.34% of the river (entrance of Yasuj City) was in a good condition, 8.33% (middle part of the river in Shah Mokhtar Area) was in a relatively bad condition and 41.66% (downstream of the river) was in a moderate condition. Despite the increase in discharge and rainfall, no significant increase in water quality was observed in the high water flow period. In this period, 25% of the river (Tang-e Tizab, Tang-e Sorkh, and downstream of Qalat) was in a moderate condition and 75% of the river was in a relatively good condition based on IRWQIsc. Comparison of the flow rates and IRWQIsc indices showed that only during the high water flow period in the lower reaches of the river, the increased river discharge enhanced the river water quality , but no relationship between the river flow and the IRWQIsc was found at the upstream part of the river and in the period of water scarcity.