Flood intensity
Food intensity may be described by height, class, depth, flow rate and speed.
Height
Flood height is often described in relation to a fixed marker, such as a post with heights, marked on it, often placed in an arbitrary position near the river.
Class
Floods may also be described in terms of classes. Definitions will vary from country to country,but the following are typical :-
-Minor flooding-floods that causes inconveniences, such as the closure of minor roads and the sub-submergence of low-level bridges.
-Moderate flooding-low lying areas are inundated, requiring, the removal of livestock and evacuation of some houses, main traffic bridges may also be submerged.
-Major flooding-extensive rural areas are flooded, with properties and towns isolated, large urban areas are also flood.
Depth
Another way of describing the intensity of floods is to relate flood heights to the floor levels of buildings that may be affected. This gives an idea of depth and is very useful for planning evacuation, land use and building.
Flow rate
Flow rate describes the volume of water flowing past a particular point in a given time period, and the units are eithe cusecs [cubic feet per second] or cumes [cubic meters per second]. This method of description is often used in relation to dam safety,as a very high flow rate over a dam with insufficient spillway capacity may lead to dam failure.
Speed
Flood intensity may also be described in terms of the speed of the water at a given point.This is a useful measure since,coupled with water depth, will indicate the scale of damage of which the moving water is capable.
Describing the speed of floodwater also makes it easier to determine when and where rescue boats can be used-boats will not make headway against water that is moving at the normal speed of the boat or faster.
Flood frequency or likelihood
Flood frequency or likelihood is often described in terms of average recurrence interval [ARI] and annual exceedence probability [AEP]
Flood extent
The extent of a flood is best described using a map. Some flood maps may be used to describe the flood for an entire country, or they may detail particular sections of rivers.
Flood manageability
Flood manageability is a measure of the degree to which floods can be prevented, prepared for, responded to and recovered from.