As the floods of 2007 continue to sweep through the UK affecting millions of people and causing billions of pounds damage, many people are asking why this has happened again. Did we learn anything from the floods of 2005? Have we made any changes to prevent the devastation from reoccurring? To answer these and other questions we need to first examine the main factors which have contributed to the severity of the flooding we have witnessed this summer.
Some of the prime factors which contribute to flooding are:
- The amount of rainfall in a given period of time. If the amount of rain that usually falls in a month comes down in the period of an hour there is little time for the water to be absorbed into the earth or diverted into storm systems, the water has nowhere to go except to follow the natural dips and channels in the landscape, be it streams, rivers, roads, ditches or low-lying properties.
- The angle of the landscape. The steeper the surface, the quicker the run-off. Rain falling on a flat field has more time to be absorbed than rain falling on a steep slope.
- The permeability of the surface the rain falls onto. If the surface if highly permeable, such as a field or a beach, the water is absorbed more easily. If the surface is hard (impermeable), like the urban landscape of cement, concrete and asphalt, then water cannot easily be absorbed and, with nowhere to go, it is diverted and continues to flow towards lower lying areas.
- The amount of vegetation and woodland in an area. The more there is in a flood basin, the more there is to absorb the run-off. As towns and cities expand, the amount of natural vegetation and woodland shrinks lessening the absorption capability of the earth.