Hard & Soft Engineering

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Flood Control – Hard & Soft Engineering Techniques

Rivers are a natural flow of water, and since the beginning of time, humans have tried to harness the energy of rivers and change their direction. This interference often leads to flooding. Sometime when a river floods it becomes necessary to intervene with its course and use modern techniques to reduce the risk of flooding and to ensure the passage of water flows downstream and away from the affected area as quickly as possible.

Hard Engineering Techniques

Below are diagrams explaining some commonly used hard Engineering Techniques:

 Revetments. Brick, concrete, wooden pile, sheet steel, rock or wire mesh structures

designed to reduce bank erosion and to prevent meander development and thus to protect

homes and farmland from erosion.

 Wing Dykes and training walls. These built out from the bank towards the centre of the

channel in order to direct the fastest river current or thalweg away from the bank. This

decreases bank erosion and increases the river’s velocity in the centre so that it erodes a

deeper, navigable channel, which is self-dredging.

Channelisation. This is where the river is straightened out bout in terms of its course and in terms of its bed and sides. This is done to reduce the friction that sides have on the water and this in turn increases the water velocity. A faster flowing river also prevents sediment dropping on the riverbed and reduces the need for dredging. This also has a knock-on effect in that it protects the banks from erosion, and protects upstream from flooding.

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Realignment/Diversion. This is where a meandering river has a new straighter channel cut, to provide a shorter and alternative route, often this new channel is concrete lined to aid flow and reduce flooding. Realignment also steepens the gradient of the river and aids navigation for boats and water-borne craft.

Levees.  Used to hold and contain water, so that the floodplains can, be developed.

(A side view of a levee – Picture obtained from http://www.publicaffairs.water.ca.gov/newsreleases/2006/03-22-06levee.jpg)


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