Floods Hard and Soft Engineering Lo; to understand the sustainability of differing flood protection methods

Flood Damage Injuries and loss of life Social disruption Income loss Emergency costs Physical damage –Structures, utilities, cars, crops, etc. Lost value of public agency services –Police & fire protection, hospitals, etc. Tax loss –Property and sales

Flood Hydrograph Peak Rising Limb Recession Limb Time Discharge, Q Beginning of Direct Runoff Base flow Recession Base flow Recession Peak Precipitation Basin Lag Time of Rise End of Direct Runoff Base flow

Hard Engineering This uses technology, large amounts of money to try and control the river. It can prevent floods in the short term. In the long term the river will try to get out of this ‘straight jacket’ and the floods can be made worse as a result.

Dams

Straightening (or channel realignment Meanders are removed from a river, this means the water has less distance to travel and can therefore be removed quicker. However, it increases erosion and flooding downstream. Straightening increases the rivers efficiencey.

Diversion Spillways ( includes intercepting channels and flood relief channels) Floods are directed away from housing and settlements into extra land or channels. However in urban area this isn't possible, and compensation often has to be paid to those who own the land.

Flood wall

Building up of levees (embankments, flood walls, artificially enhanced levees, revetments) The levees are widened and heightened to increase the amount of water a river can carry before it floods. They are often enforced with concrete. Flood magnitude may increases due to the increased amount of water held. Increased flooding upstream and downstream, and increased erosion downstream.

Soft Engineering Often the cheaper option. It tries to work with the river. People seek to sustainably manage the river – work with the river to stop large scale damage from floods.

Afforestation Planting trees. This soaks up water. Less surface runoff. Reduces flood risk.

Flood farmland Flood farmland before waters get near the city and homes and businesses. Farmland is less costly to repair than houses and industry.

Other options Sandbagging- flood proofs homes as a last resort Insurance- spreads the cost of flood damage

Do nothing It is an option. Allow an area to flood that is less valuable (in other words not businesses).

Hard and soft options Can be at a local level or for the hole drainage basin. Depending on the value of the land/importance to protect.