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One of the most important purposes of surface water resource management is to develop predictive models to assist in identifying and evaluating operational and structural measures for improving water quality. To better understand the effects of external and internal nutrient and organic loading and the effects of reservoir operation, a model is often developed, calibrated, and used for sensitivity and management simulations. The importance of modeling and simulation in the scientific community has drawn interest towards methods for automated calibration. This study addresses using an automatic technique to calibrate the water quality model CEQUAL-W2 (Cole and Wells, 2013). CE-QUAL-W2 is a two-dimensional (2D) longitudinal/vertical hydrodynamic and water quality model for surface water bodies, modeling eutrophication processes such as temperature-nutrient-algae-dissolved oxygen-organic matter and sediment relationships.The numerical method used for calibration in this study is the particle swarm optimization method developed by Kennedy and Eberhart (1995) and inspired by the paradigm of birds flocking. The objective of this calibration procedure is to choose model parameters and coefficients affecting temperature, chlorophyll a, dissolved oxygen, and nutrients (such as NH4, NO3, and PO4). A case study is presented for the Karkheh Reservoir in Iran with a capacity of more than 5 billion cubic meters that is the largest dam in Iran with both agricultural and drinking water usages. This algorithm is shown to perform very well for determining model parameters for the reservoir water quality and hydrodynamic model.Implications of the use of this procedure for other water quality models are also shown.ii

Water quality Water Quantity Many regulating, provisioning, supporting, and cultural services are related to water. Some of the Ecosystem services that people benefit from most directly include the provision of drinking water, irrigation water, hydropower, fish, opportunities for recreation. Water temperature is a major concern in our study area because its threatened salmonid species are vulnerable to high water temperatures. Nutrients concentration are major concerns because of irrigation and drinking purposes. Water quality models are increasingly developed to achieve water quality goals and to evaluate the impacts of climate, land use, and land on the quantity and quality of land and water resources. Calibration and validation of these models are critical steps in the overall model development before using them in research and/or real-world applications. With a proper water quality model, we can develop different scenarios to find effects of management plans on water bodies. Ecosystem Services CE-QUAL-W2 Model:(Cole and Wells 2003) 2-dimensional, hydrodynamic, and water quality model (CEQUAL-W2) to predict physical, chemical, and biological behaviors of a water body