The impact of flooding

(There is a map in the AQA Geography AS book, which has a map which illustrates of all the areas at risk, but for now I shall list them).

Here are a list of places the Environmental Agency consider most at risk flooding ranging from potential areas and severe high risk areas: Newcastle, Redcar, Whitby, Hull, Heacham, Hunstanton, Snettisham, King's Lynn, London, Ramsgate, Folkestone, Hastings, Portsmouth, Southampton, Plymouth, Bristol, Cardiff, Brimingham, Manchester and Leeds. If you havent noticed all of these places are located along the coastline (mainly on the East side of the British Isles) and others are located near major rivers.

Flooding is a natural occurence, which cannot always be prevented or predicted in advance. If our climate changes as many experts predict, bringing fierce storms and wetter winters, along with a rise in sea levels, the likelihood of flood will increase.

Hydrologists try to forecast the likelihood of future flood events using past records. The data they use include river discharge recordsin relation to percipitation, and flood reoccurence interval graphs. These graphs calculate statistically the probability of flooding in the future based on past records. The further back floods go, the more accurate the prediction.

Records of a river's discharge are ranked over the longest period available, from highest peak discharge to the lowest recorded. The following formula is used to calculate the recurrence interval:

recurrence interval (years) = no. of years on record + 1 / ranking of flood being considered

When the recurrence interval is plotted against discharge as a scatter graph on semi-logarithmic graph paper, it is possible to use the line of best fit to predict when the next flood of a particular magnitude might occur. This is called the flood return period. The department of Food and Rural Affiars (DEFRA) and the Environmental Agency are the main organisations responsible for flood management of major rivers like the Thames and the Severn in the British Isles and they use flood recurrence interval graphs to plan flood defence stratergies. They recommend that densely populated urban areas area sufficiently protected against 1 in 100 year flood events but that grassland and low productivity agricultural land should not be protected at all.

In addition to studying the likelihood of flooding on an annual basis, hydrologists use past data records showing the regime or yearly pattern of dischargein relation to annual percipitation patterns. In this way the likelihood of seasonal flooding can be assessed.