Study On Impacts On Water Environment And Utilization Models Of The Wet-dry Area Of Three Gorges Reservoir

The ecological and environmental problems initiated by the Three Goreges Reservoir (TGR) Project are highly concerned since the project beguan. After the completetion of this Project, there will be a great artificial reservoir with more than 600 km long, a water surface area of 1 084 km2 and a capacity of 39.3 billion m3, which will also be important fresh water source for China in the near future. After the first water storage begun in June 2003, the water level has now raised to 139 m. And in 2006, the water level will raise to 156 m and to 175 m in the year 2009. Since the operation plan of this huge reservoir is to'store clean water and disharege turbid water', the water level will alternate between 145 m and 175 m forming a wet-dry zone. This water-level alternation is opposite to the nature alternation which is high water level in summer and low water level in winter.As the wet-dry zone in Chongqing Muncipality in the TGR Area located between 145m - 175m, based on different submerging time, the upper part (170m-175m) of the wet-dry zone is submerged much shorter than the bottom part (145m-155m). In view of this situation, three types of simulating submerging experiments were conducted to present the upper, middler and bottom parts of the wet-dry zone of the Reservoir area. The results of the experiments show that when the soil is inundated, the N and P in the soil will leach out gradually. The soil samples after wet-dry treatment have different isothermal adsorption curve which means the soil's maximum N and P adsorption capability changes under different condictions. The results also demonstrate that the quantity of N/P pollutants vary with the extraneous sources affected the soil samples.Based on the experiments data and derivated from the first order kinetics model, different leaching models of N/P under different inundated condiction were constructed to predict different parts of the wet-dry zone of the TGR area. Three pollutant leaching risk levels were given in this paper to project the quantity of N/P pollutants realsed from this zone during the first dam operation period. The projections are: under high risk level the TP, TN and NH3-N released from this zone are 1 484 2 t/a, 5 479.2 t/a and 3832.9 t/a repectively; under middler risk level, the TP, TN and NH3-N quantities released are 118.9 t/a, 4 683.1 t/a and 133.3 t/a repectively; and under the low risk level, the TP, TN and NH3-N quantities released are 14.4 t/a, 2802.6 t/a and 50.4 t/a respectively.