In 2006, China completed construction of the massive Three Gorges Dam across the Yangtze River. This EVP will look at the impact of the dam on the groundwater supply for more than 30 million people who inhabit the region.

In an effort to provide hydroelectric power, increase water supplies for domestic and agricultural uses and provide flood control, large-scale damming projects are increasingly common on a global-scale. Nowhere is this more apparent than in China, with the Three Gorges Dam on the Yangzi River serving as a prime example.

The Yangzi River’s headwaters originate in the Tibetan Plateau and drain roughly one-fifth of China’s land surface. While providing a series of benefits, that range from hydro-electric power generation to flood control to increased water storage, negative outcomes associated with disturbance of the river system(s) are also noteworthy—they include displacement of inhabitants, massive destruction of terrestrial ecosystems, alteration of aquatic/marine ecosystems (particularly fisheries) and downstream river bank destabilization.

However, there are also large-scale changes to groundwater hydrology that may have sweeping impacts on water quality and yet are largely unreported. Prominent groundwater hydrologic changes resulting from dam emplacement are a rapid rise in the water table, alteration of surface-subsurface flow, and a change in aquifer residence time.

Through hydrological-(bio)geochemical process coupling, the suitability of groundwater for consumption or irrigation may then be degraded through multiple effects: (i) Salts residing in the previously unsaturated (vadose) zone above the water table may increase groundwater salinity; (ii) toxic elements previously stabilized in the aerated vadose zone may be released to groundwater; (iii) surface or near-surface water constituents such as dissolved organic carbon may stimulate biogeochemical processes that alter groundwater chemistry, and (iv) chemicals used on the land surface (e.g., pesticides) may enter groundwater through enhanced transport pathways.

This project will use the Jianghan plain, directly downstream from the Three Gorges Dam in the Yangzi River basin, as a model test area to examine the impacts of large-scale dams on groundwater quality. Researchers will develop a hydrologic model for the plain, determine groundwater chemistry, identify reactive ‘triggers’ for degradation of groundwater quality and ascertain the combined impacts of the Three Gorges Dam and land-use change on groundwater quality.

The project’s finding will have critical impacts on accurately evaluating potential negative effects on the viability of water resources for the region’s more than 30 million people and the environment.