Vertical Thermal Distribution at the near Dam Region of the Three Gorges Reservoir in the Initial Impoundment Period

Water temperature plays a crucial role in water ecological environment both in the reservoir and downstream area. Three Gorges Project (TGP) is the largest hydraulic engineering in the world, and changes of water quality attract much more attention, especially in the thermal structure since initial impoundment in 2003. In order to clearly understand water temperature distribution after the initial impoundment in the Three Gorges Reservoir (TGR), we monitored the temperature distribution of the Taipingxi section which was not far from the dam from early April to the end of July in 2004. According to the analyzing of the monitoring data of transverse and vertical temperature variation, we could find that when water level went up to 135m above sea level (a.s.l.) or 139m in the initial impoundment phase, the temperature mixed uniformly in transverse direction. Excepting April, there was basically had no temperature difference in vertical direction, even in April, the maximum temperature difference was only 1.39°C within 100 meters (April 22), the average temperature gradient was only 0.014°C/m; Both the temperature of water and atmosphere have similar variation tendency, but the response of the water temperature to atmosphere is delayed, especially the bottom water temperature. The result indicate that the reservoir displayed a mixed thermal structure during initial impoundment phase, therefore, the release had no change before and after impoundment, also had little influence on the aquatic organism and crops at downstream , the work provide a scientific basis for the development of pollution control and ecological protection measure.