Document Type : Complete scientific research article
Authors
1
Department of Hydrology and Water Resources, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran
2
Department of Civil Engineering, Jundi-Shapur University of Technology, Dezful, Iran
Abstract
Background and objectives: The wind, as one of the most effective factors on evaporation from the surface of water sources, such as reservoirs of dams, plays a significant role in estimating the volume of losses due to evaporation and thus protecting water resources. However, in most evaporation estimation methods, such as experimental relationships, evaporation pans, and even new methods such as the use of satellite images, wind is considered as a constant parameter. The wind parameter has a spatial distribution under the influence of the elevations overlooking the lake and water levels. On the other hand, simulating the spatial changes of the wind and investigating its effect on evaporation, as one of the factors affecting the water cycle, is time-consuming and difficult due to the complexity of the calculations. Failure to apply wind location changes will reduce the accuracy of the calculated evaporation and as a result, it will be difficult to access the exact amount of evaporation losses.
Materials and methods: In this study, to calculate the effect of spatial changes of wind on evaporation losses from the Dez Dam reservoir located in Khuzestan province and the southwest of Iran, the combination of the CE-QUAL-W2 model and Bowen Ratio Energy Budget (BREB) method was used. The wind shelter coefficient (WSC) as one of the input parameters to the CE-QUAL-W2 model, makes it possible for the model to consider the wind shelter condition in different segments of water bodies differently. However, due to the lack of access to a suitable criterion to show the wind shelter condition in different segments, before this research, the value of WSC was considered constant in all or large parts of the water body. In this study, CE-QUAL-W2 model capability was used for reservoir segmentation, and wind shelter condition was determined in each segment, using the wind shelter index (Sx). Therefore, it was possible to assign different WSC values in each segment. In this way, the thermal profiles in each of these segments, under the influence of two conditions of constant and variable wind (constant and variable WSC), were extracted and entered into the BREB method to calculate evaporation.
Results: The results showed that the application of spatial wind changes compared to constant wind conditions, improved the performance of the CE-QUAL-W2 model by 45% in the temperature calibration stage. Also, the monthly evaporation from the lake increased by 13%.
Conclusion: This study, introduced a standardized method for simulating the effect of spatial wind changes on evaporation from water surfaces. So that, it was possible to quantify the effect of wind on evaporation and as a result water losses from the lake, by comparing two conditions of variable and constant wind, in different segments of the studied lake.
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