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.
Flooding and DEFRA
• 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.
• 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?
Mappleton is located on the
Holderness Coastline.
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.
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
Disadvantages
Wooden 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.