Simulating Water Temperature Dynamics for Sustainable Reservoir Operation: A Case Study of Yangqu Reservoir in the Alpine Yellow River Region

The Yangqu Reservoir is a representative example of a new alpine channel reservoir, making it particularly important for understanding early-stage thermal evolution to ensure regional ecological sustainability. Using high-frequency monitoring data from a water temperature chain within the reservoir area, along with two field measurement datasets, a three-dimensional water temperature model was established using MIKE3 to simulate and predict the water temperature in the reservoir during its initial period of water storage and operation. Prototype observations and simulation results indicate that the vertical distribution of water temperature near the dam is uniform throughout the water storage period. Once storage is completed, the water temperature exhibits seasonal patterns: heating in spring, stratification in summer, a decline in autumn, and stability in winter. During the summer, stratification intensity reaches its peak, with a maximum temperature difference of 13.2 °C between the surface and bottom layers. In winter, the overall water temperature within the reservoir maintains a range of 2.1 to 3.6 °C. Spatially, the water temperature during the warming period is ranked as follows: “the tail of the reservoir < the central part < in front of the dam”. During the cooling period, this order reverses, with the tail of the reservoir being the most affected. A significant lag effect is also observed in front of the dam. These findings demonstrate that the proposed MIKE3 three-dimensional water temperature model is highly applicable and accurate for predictions in this type of reservoir. Ultimately, this model can provide a valuable theoretical foundation and data support for mitigating downstream cold-water pollution, optimizing hydraulic structures (such as ecological retaining walls), and promoting the eco-environmental sustainability of new reservoirs in alpine regions.