Causes of floods
heavy rainfall and thunderstorms over a short period;
prolonged, extensive rainfall;
high tide combined with stormy conditions.
faulty sewer networks;
poor or insufficient drainage networks;
inadequate maintenance of watercourses.
inappropriate development in flood plains.
Types of floods
Coastal flooding River Flooding
Heavy storms or other extreme weather
conditions combined with high tides can
cause sea levels to rise above normal,
force sea water to the land and cause
coastal flooding. Proper flood defences
need to be in place to safeguard life and
property. The Environment Agency and
SEPA constantly monitor sea levels and
release flood warnings when required.
This type of flooding, where a river
bursts or overtops its banks and floods
the areas around it, is more common
than coastal flooding in the UK. River
flooding is generally caused by
prolonged, extensive rain. Flooding can
be worsened by melting snow. Flooding
can also occur if the free flow of a river
gets blocked by fallen trees, natural
overgrowth or rubbish.
Grondwater flooding sewer Flooding
Groundwater flooding can occur when
water levels underneath the ground rise
above normal levels approaching the
surface. It is usually caused by
prolonged periods of rainfall.
Groundwater flooding can last for
weeks and months.
Sewer flooding may result from a
failure of the sewerage system. It may
also happen when the sewer system
does not have enough capacity to take
water entering the system from heavy
rainfall or river or highway flooding.
EFFEcts of floods
The primary effects of flooding include loss of life, damage to buildings and other
structures, including bridges, sewerage systems, roadways, and canals.
Floods also frequently damage power transmission and sometimes power generation,
which then has knock-on effects caused by the loss of power. This includes loss of
drinking water treatment and water supply, which may result in loss of drinking water
or severe water contamination. It may also cause the loss of sewage disposal
facilities. Lack of clean water combined with human sewage in the flood waters raises
the risk of waterborne diseases, which can
include typhoid, giardia, cryptosporidium, cholera and many other diseases
depending upon the location of the flood.
Damage to roads and transport infrastructure may make it difficult to mobilise aid to those
affected or to provide emergency health treatment.
Flood waters typically inundate farm land, making the land unworkable and
preventing crops from being planted or harvested, which can lead to shortages of
food both for humans and farm animals. Entire harvests for a country can be lost in
extreme flood circumstances. Some tree species may not survive prolonged flooding
of their root systems
The most dangerous floods
Floods in China in 1931
St. Felix's Flood in Netherlands in 1930
Hanoi and Red River Delta flood in North Vietnam
Eastern Guatemala flood in 1949
Bangladesh monsoon rain 1972
St. Marcellus flood in Germany, Denmark and
Netherlands in 1362
Vargas mudslide in Venezuela in 1999