Introduction

Talvar Reservoir Dam, built across Talvar River, is located on 152 km southwest of Zanjan and 7 km southwest of Hassan Taimur village in Bijar County, Kurdistan Province. This dam is made of gravel soil with a clay core. Considering the volume of 50-year sediment, its useful volume of the reservoir is estimated to be about 2.404 million cubic meters. Zanjan Regional Water Company is the operating agency of this project. The Talvar Reservoir is operated with the aim of providing drinking water, industrial water use, and irrigation of agricultural lands in Hamadan, Kurdistan, and Zanjan provinces. Water withdrawal to meet the drinking and household needs of important areas such as Hamadan city, as well as the occurrence of problems such as the reduction of flow input to this reservoir compared to the initial estimation/estimated value, make it necessary to put special attention on the water quality of the Talvar Reservoir. Accordingly, the studies on "Water Quality Modeling of Talvar Dam Reservoir" have been notified to the Sazeh Pardazi Iran Consulting Engineering Co. by the Regional Water company of Zanjan.   The key objectives of the study of the Water-Quality Modeling of Talvar Dam Reservoir are as follows:

• to improve understanding of the water quality status and its pollutant sources at the level of the dam's catchment area and reservoir.
• to investigate the thermal stratification and eutrophication status of the dam reservoir.
• As a result:
• Provide the possibility of appropriate planning for the exploitation of the Talvar Dam reservoir water in accordance with drinking, agricultural and industrial uses.
• Determine limitations for possible revision of water resources planning with regard to quality considerations.
• Minimize issues and problems during exploitation with regard to the retention of water in the reservoir and the possibility of eutrophication phenomena.