Water Quality, Sedimentation, and Hydrological Changes Due to the Construction of Large Dams: A Three Gorges Dam Focus

The Three Gorges Project, located on the Yangtze River outside of Yichang, China, brings to the forefront of the world stage awareness of the environmental effects of creating a dam and reservoir system. It is especially relevant today with the talk of exploiting renewable energy sources such as hydropower dams. This paper discusses the experiences of an undergraduate civil engineering major who visited the project in order to better understand those impacts. The paper first looks at the negative environmental impacts such as increased sedimentation and nutrients in the reservoir and increased erosion downstream. Large dams have been known to decrease the upstream water quality by introducing an increase in nutrients from agricultural runoff. They also block sediment which can collect on the upstream face of a dam. This causes the water downstream to have a reduced sediment load resulting in increased erosion. Also, peak water discharge is decreased which is detrimental to flood plains that require a flood to renew their nutrients. Regarding benefits, this work will quantify the reduction in coal use and its contribution to greenhouse gasses. Also discussed is the increased shipping capacity afforded by the dam construction - a 280% increase. This substantial cargo capacity not only provides economic efficiencies, but it also reduces carbon emissions when compared to terrestrial transportation. Lastly, the downstream flood control benefits, which are projected to reduce the ten-year flood to a hundred year flood event, will be discussed.