River flooding and management

What is river flooding?

River flooding occurs when a river overflows its banks and floods the surrounding land, often due to a combination of physical and human factors.

what are the two main factors increasing flood risk in the UK

1. increased frequency of storms as a consequence of global climate change

2. land use change as a result of the UK’s growing population

How does prolonged rainfall cause river flooding?

It saturates the soil, reducing infiltration and increasing surface runoff, which can overflow the river’s capacity.

How does heavy rainfall cause flooding?

Intense rainfall can lead to a sudden increase in discharge, overwhelming the river before water can infiltrate the soil.

How does snowmelt lead to flooding?

Melting snow adds a sudden volume of water to the river, especially in spring, causing it to overflow.

How do steep slopes contribute to river flooding?

Steep slopes cause rapid runoff and reduced infiltration, quickly increasing river discharge.

Why does impermeable rock increase flood risk?

Impermeable rock (e.g. granite) prevents water from soaking into the ground, causing more surface runoff and increasing river levels.

How do small drainage basins increase flood risk?

Water reaches the river quickly, giving less time to respond, increasing the chance of flash flooding.

How does urbanisation cause river flooding?

Towns and cities have impermeable surfaces (like concrete and tarmac), which reduce infiltration and increase surface runoff.

How does deforestation lead to flooding?

Without trees to intercept rainfall, more water reaches the ground quickly, increasing surface runoff and flood risk.

How can agriculture contribute to flooding?

Overgrazing or compacted soil from farming reduces infiltration, increasing surface runoff into rivers.

How does climate change increase flood risk?

It causes more extreme weather, like intense rainfall and storms, which increase the frequency and severity of flooding.

how does increased building on flood plains increase flood risk

flood plains are areas naturally prone to flooding and building settlements on them increases the risk to developed areas

more people living on flood plains mean that there are more people at risk of flooding if flood defences fall

What are the social impacts of river flooding?

Flooding can damage homes, displace people, cause injuries or deaths, and lead to disease outbreaks from contaminated water.

What are the economic impacts of river flooding?

Flooding damages businesses and infrastructure, causes transport disruption, and results in expensive repairs and insurance costs.

What are the environmental impacts of river flooding?

Flooding can cause erosion of riverbanks, destroy wildlife habitats, and spread pollutants into rivers and soil.

Farmland can be ruined by silt and sediment deposited after a flood

What is hard engineering in flood management?

It uses man-made structures to control rivers and reduce flood risk, e.g. dams, embankments, and channel straightening.

How do dams and reservoirs reduce flood risk?

They store excess water and control the release of river flow during heavy rain.

What are embankments (levees) and how do they help?

Embankments are raised riverbanks that increase the river’s capacity, helping to prevent overflow.

How does channel straightening reduce flood risk?

It makes the river flow faster, helping it carry water away more quickly.

how do floodgates help to protect against flooding

built on river estuaries to stop flooding from storm surges, they can be shut when there’s a surge forecast to prevent flooding

They are very expensive to build and need to be maintained regularly

how do demountable flood barriers protect against flooding

provide temporary protection against flooding, the barriers are only put up when there’s a flood forecast so there’s always a risk they might not be put up in time, they are quite expensive to build but don’t spoil the look of attractive locations

What is soft engineering in flood management?

More sustainable, natural methods to manage flooding, e.g. afforestation, floodplain zoning, and river restoration.

How does afforestation reduce flooding?

Trees intercept rainfall, increase infiltration, and slow down surface runoff.

how does flood plain retention reduce flood risk

involves maintaining the river’s flood plain, not building on it, helps slow floodwaters down and maintain the flood plain’s ability to store water

no money has to be spent on building defences but it restricts development and can’t be used in urban areas

how does river restoration help with floods

involves making the river more natural by removing man made levees so that the flood plain can flood more naturally, so there’s less risk of flooding downstream because discharged is reduced

very little maintenance required, however river restoration can increase flood risk especially if nothing is done to prevent major flooding