Flooding is a natural event, but becomes a natural hazard because of human settlement close to rivers. There have been methods developed over the years of dealing with, predicting and preventing flooding. They can be divided into soft engineering (less expensive, less environmental damage) and hard engineering (more expensive, less sustainable).
Soft Engineering
Floodplain Zoning
- A method of hazard mapping and land use management developed by environment agencies to assess flood risk before building on flood plains. The Department for Environment, Food and Rural Affairs, DEFRA' website can be found here: http://apps.environment-agency.gov.uk/wiyby/37837.aspx and on that site, any postcode can be entered to assess its risk of flooding.
- Advantages include: avoiding building on high risk flood plains, avoiding damage to property, more green space, more agriculture, increased infiltration.
- Disadvantages include: doesnt help areas where floodplains are already urbanised, planning issues harder to enforce in LEDCs as this is more of an MEDC solution due to technology and surveying.
Warning Systems
Washland and Water Meadows
Restoration and Afforestation
- Sirens, social media, public announcements can be made to prepare the population of an impending flood.
- Advantages include: In a more connected world, many people can be warned in seconds thanks to social media, especially in MEDCs, weather watching agencies are becoming more and more accurate and this makes us more prepared for floods.
- Disadvantages include: can be extremely difficult to predict flash flooding like in Boscastle, LEDCs are less connected to social media so warnings are more difficult to make in poorer countries.
- Example: The UK Met Office will issue weather warnings from yellow to red based on the predicted severity of the weather event.
Washland and Water Meadows
- The river is allowed to flood naturally to washland and meadows that exist on its floodplains.
- Advantages: Habitats for animals provided, improved agricultural land, low maintainance.
- Disadvantages: Land cant be used during flooding events.
- Example: The River Trent UK, the washlands are exceptional grazing areas for sheep.
Restoration and Afforestation
- Managed rivers are returned to natural state with trees planted and old channels restored.
- Advantages include: improved environment, sustainable, habitats created/restored, can be low cost.
- Disadvantages: If not managed correctly, invasive and alien species can be introduced accidentally.
Hard engineering
Flood Relief Channels/ Spillways
Straightening and Channelisation
Dams
- The channelling of water around an urbanised area. Spillways will take water from upstream of a town and return it downstream of the town.
- Although this method will save a specific urbanised area from flooding, it will often cause flooding to happen downstream anyway.
Straightening and Channelisation
- River channels are widened and deepened, and meanders are eliminated to allow more water to flow through the channel more quickly.
- Advantages: Moves water away from vulnerable areas quickly
- Disadvantages: Flooding can occur downstream, wildlife habitats lost, increased erosion downstream due to velocity of water.
Dams
- Water held back during flooding so discharge is reduced, water is then released when there is low flow to prevent flooding downstream.
- Advantages: Hydro electric power can be generated meaning not only can they help prevent flooding but also generate renewable energy, reservoirs have multi-purposes including leisure activities, habitat formation
- Disadvantages: Hugely expensive to build, sedimentation issues, some settlements may be lost e.g ladybower reservoir swallowing derwent village, difficult to construct in LEDCs because of huge cost involved, and the climate in some poorer countries.
Levees and Embankments
- Levees are a natural depositional feature of rivers, but can be built upon and strengthened to prevent flooding.
- Advantages: If reinforced by by concrete, erosion is decresed, the floodplain behind them can be utilised for urbanisation and agriculture
- Disadvantages: If breached, can increase flood levels, need constant maintenance to retain effectiveness.
Flood walls
- Vertically constructed walls of concrete or metal shuttering at the edge of the channel.
- Advantgase: cheap and quick to erect, useful when there is not much space
- Disadvantages: never totally waterproof, quite ugly.