geoplanet

Flooding

 

 

 

 

 

Flooding:

Floods occur when a river bursts its bank and the water inundates the surrounding areas. Flooding can be influenced by both human and environmental/natural (physical) factors.

Physical Factors:

• One common influence is severe weather. (Heavy or continuous precipitation (rain)).

• Impermeable surfaces such as saturated or baked soils increase surface flows and the amount of water entering river systems

• Thick layers of snow can potentially flood areas because of the vast amount of water that is melted from the snow

• In areas with steep gradients, there is less time for precipitation to permeate into the soils therefore shortening lag time (time take for the water to reach the river)          

Human Factors:

• The leaves and soils of trees intercept contact of precipitation; when cut down (deforestation), the water can flood on when overloading on the ground by vast volumes or heavy rainfall

• In urban areas impermeable surfaces (such as roofs) disallow the water to penetrate through the surface therefore, (as effect), are transported from the drains to rivers

• Due to farming practises and fossil fuels, global warming has triggered the extreme weather conditions such as hurricanes and unpredictable rain patterns

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Forecasting Flooding:

In Britain, sophisticated technology and satellites are used to predict future weather conditions. The MET Office issues a warning when there are potential dangerous problems. In addition, river levels are monitored by the Environmental Agency by plotting the measured distance between the peak discharge and the heaviest rainfall on a hydograph, (otherwise referred to as the lag time). The shorter the lag time the more chances there are of a flooding. (Heavy precipitation à quick infiltration à higher chances of floods).  In case of certain scenarios occurring, local authorities have emergency actions to react, for example, aid kits for evacuations.

Building Design to Prevent Problems:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Planning:

Local authorities try to avert flooding by prohibiting certain builds in area of floodplain lands or areas that are exposed to floodings. In exchange of these new homes and buildings, local governing place flood defence programmes/features into the area. For instance, soft or hard engineering:

Hard – Tend to change the natural river channel to avoid triggering such occurrences, (expensive engineering methods).

Soft – Generally tends to be natural and less expensive as you are not involving change in the natural areas of the river channel. However, a drawback of doing so is that they are less effective to hard engineering and that they have an overall expensive fee to the construction.