Prediction and Prevention of the effects of coastal flooding by forecasting, building, design, planning and education.

Prediction and Prevention of the effects of coastal flooding by forecasting, building, design,

planning and education

Coastal Flooding

• In England 2.1 million properties are at risk from flooding. Nearly 50 per cent of these properties are at risk from flooding from the sea.

• There are a number of ways that the effects of flooding can be reduced. Householders can be warned about a flood so that they can take precautions. This is done in the UK through a chain of events.

Flooding and the Met Office

• The Met Office predicts the likelihood of a coastal flood and gives information to the public through weather forecasts and news broadcasts on the television.

• These advise householders to be proactive and either ring a flood hotline number or go onto the Environment Agency website to check the likelihood of a flood in their area.

Flooding and the Environmental Agency

• On the Environment Agency website there will be information on the likelihood of a flood.

• This will be identified by a system of warning codes: flood watch, flood warning, severe flood warning and all clear.

• These warning codes give people information on what to expect and how to react.

• DEFRA (The Department for Environment, Food and Rural Affairs) has the responsibility for deciding which areas of the coastline are going to be defended against the risk of flooding.

• The Environment Agency then organises for the defences to be built and maintained.

• DEFRA provides the money for most of the work that is completed.

Flooding and DEFRA

• As well as the monitoring which is being done by the Met Office, the Environment Agency also monitors sea conditions over a 24-hour period, 365 days a year.

• The StormTide Forecasting Service provides the Environment Agency with forecasts of coastal flooding which the Environment Agency communicates to the public via their website or phone line.

• Other ways that the effects of flooding can be reduced is by building design and control.

• Before houses can be built the local authority has to give planning permission. This is not granted in flood risk areas unless a flood risk assessment has been carried out. However, some building does still take place in areas where it is not really advisable to build houses.

• By 2010 the government has indicated that planning laws will change so that all new housing in flood risk areas must be flood resistant or resilient.

Flood Warning Codes from the Environmental Agency

Soft and Hard Engineering Techniques• Coastal defences can be classified as either soft

or hard engineering techniques.

SOFT ENGINEERING:

• Soft engineering is a method of coastal management which works, or attempts to work, with the natural processes at work on the coastline and to be unobtrusive visually. It does not tend to involve major construction work, for example, beach nourishment/replenishment.

HARD ENGINEERING:

• Hard engineering is a method of coastal management which involves major construction work, for example, seawalls.

How can the coastline be protected?

How do groynes work?

Groynes trap the sand which is carried along the coast by longshore drift.

The sand acts as a natural protection against the force of the waves. The waves break onto the beach and not the cliffs.

What are the disadvantages of groynes?

In 1991 a rock revetment and two rock groynes were built. Sand accumulated and halted erosion.

South of Mappleton, the rate of erosion has increased significantly.

Material that usually moves south via longshore drift is becoming trapped within the groynes.

Now there is no beach to protect the cliffs - the sea reaches the base of the soft cliffs and erosion occurs.

Mappleton is located on the Holderness Coastline.

Managed Retreat

Managed retreat is also known as managed realignment. It involves breaching an existing coastal defence, such as a sea wall, and allowing the land behind to be flooded. This land is then left to be colonised by saltmarsh vegetation. When established, the vegetation disperses wave energy, reduces erosion rates and provides new habitats.

The first attempt at managed retreat in the UK was on Northey Island, located in the Blackwater Estuary in Essex.

Beach Replenishment

Beach replenishment is also known as beach nourishment. Beach nourishment is the process of dumping or pumping sand from elsewhere onto an eroding shoreline to create a new beach or to widen the existing beach.

Beach nourishment does not stop erosion, it simply gives the erosional forces (usually waves) something else to "chew on" for awhile.

The waves erode the nourished sand instead of destroying houses, roads or parking lots. Because nourishment doesn't stop erosion, nourishment must be repeated to maintain the beach.

How can the coastline be protected?Hard engineering techniques aim to stop coastal processes from occurring. Soft engineering methods try to work with nature to protect the coast.

What problems do sea walls create?

Why might a sea wall cause more coastal erosion?

Match the following statements to your pictures of hard and soft

engineering worksheet.

Write in pencil if you are unsure!

If you finish, use page 58/59 of the textbook to add more detail.

How does it work? Advantages DisadvantagesWooden structures break the force of the waves and trap beach material behind them.

Much cheaper than a sea wall. Effective at breaking the force of the waves.

Less durable than a sea wall – may need replacing quicker.Does not give total protection to the base of the cliff.Cost approx £1000 per metre

Large boulders on the beach – lesson the force of the waves by absorbing the wave energy within the gaps between the rocks.

Relatively cheap.Use natural material/rocks

Environmentally ugly . Can be removed by the waves due to the washing away of sand and shingle beneath.

Build up the beach by replenishing beach material, particularly at the base of structures to provide a ‘natural’ solution to absorbing wave energy.

Provides a natural solution.Natural looking – meaning it is difficult to tell management is taking place.

Can be expensive to keep transporting large amount of sand – sediment moved by longshore drfit so will need frequent replenishment unless used with other defences.

Concrete wall, curved under side to deflect the power of the waves.

They reflect rather than absorb wave energy.Most effective means of preventing erosion.

Most expensive (up to £2.5 million/km).Deflected waves often scour the base, undermining it – it may collapse in the future.

Cages of boulders built into the cliff face – small rocks help to absorb the wave energy.

Effective where severe erosion and cheaper than sea walls.

Environmentally ugly (usually used in large numbers)Cost is approx £350 per metre.

Wooden or in some cases steel structures that stop longshore drift and build up/ anchor the beach, protecting the base of a cliff.

Stops longshore drift encouraging the build up of the beach and effectively reducing erosion.

Can increase erosion further down the coast by stopping longshore drift and starving areas further down the coast of sediment. Cost approx £5-6000 each.