River Flooding and Management

Flooding

Floods can bring both advantages and disadvantages to an area. Floods can deposit rich, fertile alluvium in agricultural areas. Also, flood water can replenish irrigation channels. On the other hand, floods can destroy food supplies, homes and transport infrastructures.

What are the factors affecting flood risk?

A flood occurs when water can no longer be contained within a river channel. The flood risk can be increased by physical and human factors.

Physical factors affecting flood risk

• Precipitation – When there is intense or extended rain, the ground can become overly saturated. This condition prevents water from being absorbed, leading to quicker runoff and a higher chance of flooding.
• Geology – The type of rock in an area can affect flooding risk. Non-porous rocks, meaning they don’t let water seep through, can cause water to flow rapidly across the surface, increasing the likelihood of floods.
• Steep slopes – Water can move swiftly downhill in regions with steep terrain, such as mountains. This rapid movement contributes to a greater risk of flooding in these areas.

Human factors affecting flood risk

Some land uses increase the risk of flooding.

• Farming – Agricultural practices can influence how water moves. For instance, fields without crops, especially during winter when soils are wet, can quickly channel water. Also, ploughing down slopes can form small channels that accelerate water flow directly to rivers.
• Urbanisation – City development affects water movement as well. Hard, non-absorbent surfaces like concrete and asphalt, along with drainage systems, can speed up water flow to rivers. Plus, the scarcity of greenery means less rainwater is absorbed or evaporated.
• Deforestation – Cutting down forests impacts water transfer. Trees normally act like an umbrella, slowing down water movement and using or storing rainwater. Without trees, more water flows directly to rivers, raising the potential for flooding.

Effects of flooding

Flooding can have a significant impact on people. These are known as social impacts. Social impacts can include:

• damage to property
• injury or loss of life

Flooding can also have an impact on wealth. This is known as an economic impact. Economic impacts of flooding include:

• cost of repairs
• reduced tourism

Finally, flooding can have an impact on the surrounding landscape. Environmental impacts of flooding can include:

• loss of livestock
• loss of habitat
• destruction of crops

Managing Flooding – Hard Engineering

Dams
Although very expensive, dams can significantly reduce the risk of flooding downstream

Levees
These are man-made embankments constructed along the edge of the river. They increase the capacity of the channel to prevent the overflow of water.

The video below shows a levee constructed at Cockermouth, Cumbria following the 2009 floods.

Flood Defence Barriers
Similar to levees, only constructed from man-made materials flood defence barriers increase the channel size of a river which prevents the overflow of water.

The video below shows flood defence barriers at Cockermouth, constructed after the 2009 floods.

Managing Flooding – Soft Engineering

Afforestation
Planting more trees reduces run-off and increases interception.

Flood Plain Zoning
Floodplain zoning policies influence how land on, or close to, floodplains are used.

River restoration involves removing any hard-engineering strategies and restoring the river to its original course. This can involve making the river less straight which can slow the flow of the river.