Analysis of the dynamic impact of Three-Gorge Project on regime of soil water and salt in Yangtze River Delta

Abstract

The topography is low and flat in the estuarine region of the Yangtze River, where waterlog and salt-affected soil are 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. Based on the theory of solute transport and the principle of soil water dynamics, the model of soil water and salt transport was created, which involved root water extraction, adsorption---desorption, mobile---immobile region. To overcome numerical dispersion, the paper solved the convection---dispersion equation by Bresler algorithm, the term of time derivative used the approximate difference formula of quadratic differential coefficient based on central difference. Then, the impact of Three-Gorge Project on the regime of soil water and salt in the estuarine region by numerical simulation was studied in. The numerical simulation indicates that electric conductivity of soil one meter thick of each observed section will go down by 0.005---0.174 mS/cm as discharge increases in spring after building the Three-Gorge Reservoir, and up by 0.004---0.416 mS/cm as discharge decreases in autumn---winter. 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 km of the river, it is more possible that the soil will produce salification or secondary salinization.