Study On Distribution Of Water And Ice Temperature In Reservoir With Seasonal Ice Cover

Flow regulation caused by the hydropower projects will change the hydrological characteristics of reservoir and downstream river reaches. Water temperature, water quality and aquatic ecosystem will be affected as a result, especially for reservoirs with deep water depth. For reservoirs in frigid zone and high altitude area, water surfaces may be covered with ice because of lower air temperature and slower velocity of flow. The ice surface will change the mode of heat exchange between the air temperature and reservoir water, decrease heat lose of reservoir water, and prevent oxygen re-aeration. Water quality may be deteriorated in the case of ice cover. Based on the previous studies, mathematical model and numerical method for predicting, vertical water temperature distribution of reservoir with seasonal ice cover in freeze-up and in non freeze-up is established. The method established in this paper will provide theoretical base for reservoir operation and environmental impact assessment. The main contents of the study and results are as following:1. The three-dimensional mathematical model was used to simulate temperature distribution in Zhangfeng reservoir. The distribution of the vertical water temperature of dam is calculated in the wet year, normal water year and dry year. Vertical temperature structure in cold reservoir and the effect of the water temperature after the building of the reservoir is analysed according to the forecast results.2. Previous studies on reservoir water temperature prediction, heat transfer between air and water near water surface, ice generation and melting, process are summarized. The rules of ice generation and melting, heat transfer between air and water, and heat convection and diffusion in the water are studied in this paper. Based on the 1-D heat equation of ice cover in reservoir was established and the finite element method was proposed, the computer program was prepared and through the typical examples validate and error analysis. 3. The mathematical model and numerical method are applied in the prediction of vertical ice temperature distribution in the ice of the ZhangFeng Reservoir, and the rule of heat exchange is analysed. It is shown that the distribution of the ice temperature contours is dense in the surface and the ice temperature contours is sparse in the ice water interface.That is, in the growth of the ice, the heat exchange capacity in ice-air interface more than that in the ice water interface.The model is suitable for predicting vertical water temperature distribution of similar reservoir.