River management

Causes of flooding

A flood occurs when a river bursts its banks and the water spills onto the floodplain.

The causes of flooding are usually a result of both physical and human factors.

Physical factors are those which are caused by nature.

Human factors are when human intervention and interference create the conditions for flooding.

Illustration showing four phyiscal causes of floodingPhysical causes of flooding

Physical causes

PrecipitationThe more rain that falls onto a drainage basin over a short period of time, the more likely that there will be some flooding in a river channel.
Soil and rockDifferent types of soil and rock will dictate whether the water flows through or stays close to the surface. Once soil and rock is full to capacity, the water will become surface runoff and will run into river channels more quickly.
Land useA drainage basin with little vegetation is more likely to flood quickly as there is no vegetation to intercept the water and remove it from the surface runoff.
Steep slopesAreas where the drainage basin is small and valley sides are steep will return water to the river channel much more quickly than places where the slopes are gentler.

Human causes

Deforestation Removing trees will reduce interception and increase the amount of water going into the river system.
River management Sometimes measures taken to manage the river can increase the amount of water in the river. Putting concrete into a river to speed up the movement of water in one part of the river can cause flooding further downstream.
Global warming As sea levels rise, there will be an increase in the amount of water available for evaporation and precipitation in the water cycle. This means that more water could be falling onto drainage basins than usual.
Urban growth The concrete/tarmac roads and pipe/drain systems in urban areas can speed up the delivery of water back into the river channel making a flash flood more likely to occur.
Illustration showing four human causes of floodingHuman causes of flooding