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| Frequently Asked Questions
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| My property may be affected
by groundwater flooding, what can I do?
- What is
groundwater flooding?
- What can
I do to protect my property from groundwater flooding?
- Where can
I find out more?
What is groundwater flooding?
 Around
5 million people, in 2 million properties, live in flood
risk areas in England and Wales alone, and in Scotland
some 77,000 properties are at risk from inland flooding.
Flooding normally occurs where stream, river or other
drainage channels cannot cope with the amount of water
that is flowing into them during periods of higher than
normal rainfall, and the water breaks or overspills the
banks. This is known as surface water flooding.
It is estimated that groundwater flooding affects a few hundred
thousand properties in the UK. Groundwater flooding occurs
as a result of water rising up from
the underlying rocks or from water flowing from abnormal springs.
This tends to occur after much longer
periods of sustained high rainfall. Higher rainfall means
more water will infiltrate into the ground and cause the
water table to rise above normal levels. Groundwater tends
to flow from areas where the ground level is high, to
areas where the ground level is low. In low-lying areas
the water table is usually at shallower depths anyway,
but during very wet periods, with all the additional groundwater
flowing towards these areas, the water table can rise
up to the surface causing groundwater flooding.
Groundwater flooding is most likely to occur in low-lying
areas underlain by permeable rocks (aquifers). These may
be extensive, regional aquifers, such as Chalk or sandstone,
or may be localised sands or river gravels in valley bottoms
underlain by less permeable rocks. Groundwater flooding
takes longer to dissipate because groundwater moves much
more slowly than surface water and will take time to flow
away underground. |
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What can I do to protect my property from groundwater
flooding?
The precautions
that can be taken by local authorities or the environment
regulators to protect against groundwater flooding are
limited. Groundwater flooding is often more difficult
to prevent than surface water flooding; its not as simple
as building flood defences to prevent river water spilling
over its banks. There are some areas where groundwater
flooding has been dealt with by installing pumps to remove
groundwater and so lower the water table but these only
have a localised effect, and there is still the problem
of having somewhere to discharge the water.
For property owners, the precautions that can be taken
against groundwater flooding specifically are also limited.
If you have a basement which is frequently flooded and
you would like to use it for storage or as a living area,
it may be possible to ‘tank’ it. This involves
sealing the basement with a water-proof membrane. The Environment Agency in
England and Wales has issued a
pamphlet which explains these and other measures
that can be taken.
Given that areas prone to groundwater flooding are normally
also prone to surface water flooding, measures commonly discussed
for surface
water flooding are also relevant.
The distinction between surface water flooding and groundwater
flooding is rarely clear. Increased infiltration and a
rise in the water table may result in more water flowing
into rivers which may then be more likely to break their
banks. A rise in the water table during periods of higher
than normal rainfall may mean that land drainage networks,
such as storm sewers, don’t work properly if groundwater
is flowing into them underground. This may affect their
ability to get rid of surface water which then causes
flooding. |
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Where can I find out more?
Information on how to prepare for and cope with
surface water flooding and also on areas prone to this
type of flooding are available on the Environment
Agency and Scottish Environment Protection Agency
web sites. They also issue flood warnings that are updated
every 15 minutes. A 24-hour Floodline telephone information
service is also operated by the Environment Agency in
England and Wales and by the Scottish
Environment Protection Agency in Scotland. The number
for this is 0845 988188.
If you are concerned about flooding and would like more
detailed information, you can also contact the local office
of your environment regulator or your local authority.
Your local library may hold records of historical flood
events for your area as may the Chronology
of British Hydrological Events web site. |
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