Environmental Effect of Large-scale Hydropower Project -A Case Study in Three-Gorge Project of China

The topography is low and flat in the estuarine region of the Yangtze River, where waterlog and salt-affected soil is all through a latent threat to the agricultural development for long time. After the Three-Gorge Project is built up, the Three-Gorge Reservoir adjusts seasonably runoff will impact on the dynamic of soil water and salt in the region. These influence relations are very complicated. In spring, it will make the river water level up that discharge increases, so it will be not in favor of desalting. At the same time, mineralization degree of groundwater will decrease, in favor of desalting. In autumn-winter, it will make the river water level down that the discharge decreases, in favor of desalting. But, the mineralization degree of groundwater will increase, simultaneously salty tide invasion will strengthen, so not in favor of desalting. The elementary predicted result of numerical simulation shows that salification will be bigger in autumn than desalinization in spring. The impact degree of the project on the regime of soil salt will be gradually weakened along the river up from the estuary, the nearer to the sea, the bigger the impact, and from cross profiles, the nearer to the river, the bigger the impact. Especially within the range of 4 kilometers off the river, it is more possible that soil will produce salification or secondary salinization.