Human Interaction with Surface processes

When people build dams and levees to control river flooding, it has a major impact on the rivers ability to operate its functions naturally. For example, the three gorges dam in China. Building dams affects the rivers transport process, interefring with its ability to carry its load downstream. Instead, its sediment becomes trapped behind the dam. The 3 gorges dam in China is built along the river Yangtze, and stretches along 1.6km at 185m high. A resevoir 560km wide was constructed behind the dam,and it is used to generate power for major cities like Shanghai and Wuhan, as well as prevent flooding. These floods have killed hundreds of thousands of people in the past, however this has also prevented the rivers vital alluvium from being carried downstream. The floods have also stopped. This has saved lives but the surrounding farmland has become infertile, forcing famers to use expensive artificial fertilisers. Building levees also helps prevent floods, eg the river Rhine in Germany. Levees are raised banks deposited along the sides of rivers course, they can be naturally occruing landforms or constructed by humans as part of flood control. Humans can also raise levees to stop a river from flooding its floodplains. Floodplains are flat, fertile land along the side of rivers, and through the centuries, many have come to support vast populations of humans, such as Duisburg- Europes largest inland port, which has been built on the Rhines floodplain. Preventing rivers from overflowing onto their floodplains has stopped damage to economically important areas such as factories and transport industries. Because levees are so high, the river channel cannot flow natrually, so it deposits its load on the riverbed. Overtime, this means the riverbed rises above the level f the floodplain and so the levees are the only things holding them back. This creates a need for higher, stronger levees which are exspensive to build and maintain. Floodwater which would normally escape onto the floodplain is now funnelled downwards where it can cause massive damage. Levees also cause the river to flow faster, in narrower channels. The Rhine now flows 30% faster than it did before the levee was built.