Abstract:

EFDC model was used to simulate water temperature of the Ertan reservoir from February 28th to July 31th,2006.Traverse direction of the reservoir was generalized into a grid and the average width was 400m;longitudinal direction of the reservoir was divided into 139 sections and the grid spacing ranged from about 500 m to 1200 m;vertical direction of the reservoir was divided into 40 layers.Thus， the total number of the research domain grids was 5 560.In order to improve simulation ability of the EFDC model,a preliminary exploration of the uncertainties related to model parameters was made.By analyzing parameters related to heat exchange and transfer,we have found that, surface water temperature would increase and bottom water temperature would decrease,when the value of proportion of fast wave in shortwave radiation (FF) or coefficient of shortwave radiation slowly attenuated in water (SS) increased.On the other hand, the coefficient of shortwave radiation rapidly attenuated in water (SF) had no significant influence on water temperature.Then,parameters were calibrated by comparing the simulated and observed water temperature at different reservoir sections in different time period.The modeling results indicated that the EFDC model could well reveal water temperature stratification structure and their development processes of large deepreservoir.On this basis,the law of water temperature stratification was analyzed.Water temperature stratification phenomenon could be observed in all the months during the simulation period.Stratification structure was simple and a single thermocline was appeared in March.And temperature gradient of the single thermocline gradually became larger from April to June and finally a double thermocline was formed in July.Surface water temperature significantly increased from March to July due to the influences caused by shortwave radiation and air temperature (from about 14℃ to 25℃).Meanwhile,bottom water temperature changed little during this period because the heat was difficult to transfer from surface to bottom (around 11℃).It also could be seen that,temperature of discharged water after the construction of dam was different from the natural river water temperature at the same place.Temperature of discharged water was higher than natural river water temperature in March,June and July;and lower than natural river water temperature in April and May.Therefore,the reasons and influences of water temperature difference due to the construction of dam were analyzed.By doing this,we attempt to provide some scientific basis for water intake design and operation management of reservoir in order to reduce the influences of water temperature stratification and protect the ecological environment and aquatic biodiversity of the downstream river