Improving CE-QUAL-W2 calibration using a terrain-based wind sheltering coefficient tuning method

Abstract

Abstract Effective studies have been conducted in the field of reservoir hydrodynamics and water quality simulation, including thermal stratification, selective withdrawal, and eutrophication modeling. In this model, the wind sheltering coefficient (WSC) plays a significant role in the calculations of the wind-induced shear stress and subsequently the reservoir thermal gradient. Due to the spatial variations of the wind across the water surface, the lack of a criterion for assigning values to the WSC, hinders the accurate tuning of its values during the calibration process. The trial and error method, which is time-consuming, is used to determine WSC. Therefore, in this study, the wind shelter index (Sx) was introduced to the CE-QUAL-W2 model as a criterion to achieve the spatial distribution of the wind shelter condition of the points on the water surface. A more accurate and faster calibration method was devised using Sx to determine WSC and estimate the thermal gradient in different parts of water bodies. For this purpose, the Dez Dam reservoir in Iran was divided into different segments, and the average Sx in each segment was calculated through a 30 × 30 m grid located on the lake's surface, and replaced the WSC values. The results showed that by using Sx in the temperature calibration of the CE-QUAL-W2 model, there was no need for trial and error in finding the best value for WSC and the RMSE was reduced from the 0.35–0.44 range to the 0.20–0.25 range.