Hard and Soft River Defences

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Hard and soft river defences on the Mississippi

The dams in the Mississippi river are a hard flood defence. There are two different types of dams on the Mississippi River, wing dams and closing dams. Wing dams are built close together with brush and stone structures that extend from the river bank to the channel and closing dams are used to block connections between the main channel and side channels of the floodplains. The advantages of building dams on the Mississippi are that they enhance the electricity generating capacity for the surrounding regions and the river won’t dry up but just waits for more water to arrive. The disadvantage of building dams on the Mississippi is that it could cause flooding if there are too great amounts of water. The flow of major tributaries in places such as Missouri, Ohio and Tennessee has been controlled by a series of dams. The upper st Anthony falls dam is situated on the upper course of the Mississippi river. It turns the current flow into surface storage, and holds back water to form navigation pools.

Levees were designed to protest the populated areas by restricting current flow to avoid floods. They were first natural creations by the rivers fluvial processes, and were increased in size and strength to try to eliminate the flooding problem. They work by creating a higher and stronger barrier so that when the river is flooding the water is still held in place, and doesn’t spill out onto the flood plain. The extension of the levees along the Mississippi, and of its tributaries, means that water is more confines, so although it reduces flood risk upstream, due to the water rising higher and flowing faster, the flood risk downstream is increased.

Dredging can be used to create a deeper channel so that greater volumes of water can pass through, however flood risk is increased downstream. This can be seen at numerous points along the Mississippi river, and also where the upper st Anthony falls dam is, dredging has...
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