Hard engineering

Revetments• Revetments are sloping structures placed on banks of a

river in such a way as to absorb the energy of incoming water. It is usually made from a variety of very resistant rocks such as granite and limestone. The size and mass of the riprap absorbs the impact energy of the river, while the gaps between the rocks trap and slow the flow of water, lessening its ability to erode soil or structures.

Channellisation• The characteristics of a river channel, namely width,

depth and sinuosity are adjusted to the natural flow regime at bank full discharge. People attempt to manage river channels by changing some of these variables in order to change channel characteristics such as speed of discharge or sedimentation. This modification is known as channellisation. The river becomes more efficient due to the water having less contact with the banks of the channel.

Man-made levees

• As levees take such a long time to form naturally humans have created man made levees to help protect their land. These anthropogenic levees not only decrease the chance of flooding by building a wall to prevent the flow of water but they also increase the channel efficiency by increasing the channel capacity.

Wing dykes• Wing dikes are rock structures extending from the

river bank out into the river channel. Some dikes may be more than a mile long and often occur in groups or dike fields. The purpose of a dike is to direct flow into the main navigation channel away from banks or side channels. Dikes help reduce sedimentation in the main channel and can protect banks from erosion.

Realignment• The channel is straightened and therefore

becomes more efficient. This is due to the fact that the water in the channel now has less contact with the banks. The purpose of realignment is to increase the gradient of the long profile. This reduces the risk of flooding upstream.