Floods are a natural event and only become a hazard when they
affect people of property. People have chosen to build their homes close to the
river and can take precautions such as:
house design which raises the floor level above normal flood
heights;
interior room design which minimises flood damage, e.g. tiled
floors;
light furniture which can be quickly and easily moved upstairs
should a flood occur;
Removable flood walls that can be opened in summer to provide a
river view.
Local authorities are now controlling the location of new
buildings and the construction methods used, so that buildings are able to cope
with floods when they occur.
2. Dams and reservoirs
Built upstream for hydro-electricity and to regulate river
flow. The aim is to help prevent flooding and to release water gradually in
times of low rainfall in order to make the river navigable all year round. Dams
are multipurpose schemes which:
control flooding
provide a water supply
produce hydro-electricity
improve navigation
increase afforestation
reduce soil erosion
encourage industry
encourage tourism
3. Flood Retention Basins and Impounding Dams:
'Impounding Dams' are valleys filled with water which provide
drinking water, produce electricity or supplement low flows. The water stored in
impounding dams is drawn off from flood waters and during flood periods the
water is merely moved for a time from one place to another. 'Flood Retention
Basins' are only filled with water during periods of flood, after which they are
emptied in order to be ready for the next flood.
4. Increasing the height of the levées
It has been suggested that higher embankments should be built
and the river deepened but, where this has been done, (e.g. the Mississippi) it
has produced rivers flowing many metres above the surrounding floodplain. As the
levee is built up, sediment in the river grows too; the river beds – and the
water levels rise. This leads to disaster when the barriers collapse.
5. Flood relief channels
To siphon off the Rhine flood water when the delta near the sea
becomes overloaded.
6. Making the course straighter and shorter
This aims to get rid of the flood water as quickly as possible.
By shortening the distance, navigation is made easier, but the gradient and
therefore the speed of the river is increased.
7. Afforestation
Trees delay and reduce the amount of water reaching the river.
8. Floodplain land use zoning
Land can be zoned for uses that will not be damaged by winter
floods e.g. pasture, forestry and parks
9. Floating Towns
The Dutch are pioneering floating
towns to cope with rising tides and river flooding. In the short term,
however, floating houses are no replacement for conventional flood defences.
10. Room for the River
This reflects a new philosophy that humans should adapt to the
shape of river basins that naturally result from flooding histories. This
programme is currently being translated into land use change and relocation of
inhabitants and dykes on certain floodplains. Arable land is being converted to
forest, marsh or wet grazing meadows. Inhabitants are being relocated, with
compensation, to higher elevations, and dykes are being relocated back from the
main channel such that the entire floodplain cross section can accommodate a
much larger volume of water.
Measures taken include:
An increase in 'water meadows' which can be allowed to flood
when necessary. The sealing of the soil surface with tarmac or concrete in
vulnerable areas is being limited to slow the water run off into the rivers.
Ground coverage of vegetation with woodlands and grasslands is
being increased.
The use of fertilisers on soil is being very carefully monitored
because these affect the soil structure and its ability to retain water.
Adequate maintenance of dykes and flood walls.
To allow more space for trees on the floodplain, metres of silt
accumulated over many years has been stripped and deep trenches constructed.
(See diagram below).
Room for the river: floodplain management
Coordinated water management policies across national borders
is necessary if winter floods are to be avoided in the future, e.g. buffer
zones, dykes, water flow regulation. The job of developing these flood control
measures will cost hundreds of millions of pounds. However, if they are adopted,
not only will the dangers of flooding be reduced but they will also help to
protect the environment in areas along the banks of the affected rivers. It must
not be forgotten though that flooding is, for the most part, controlled by
nature and humankind can influence the impact of flooding to a limited degree
only.
