Understanding Flood Risk

Understanding types of flood and the roles and responsibilities of Flood Risk Management Agencies.

Understanding Your Flood Risk:

Flooding is more than just “too much water”. It is a personal, often life‑changing experience that can leave people feeling overwhelmed and unsure where to turn. Whether you are protecting your home for the first time or recovering from a recent flood, understanding why and how water enters your property is an important first step towards taking back control.

At the National Flood Forum, we know that a properties can be at risk from more than one source of flooding. By understanding these risks, you can be better prepared for the future.

Types of Flooding

Flooding can happen in different ways, depending on the source of the water and local conditions. Understanding the type of flooding that affects your home or community can help you take the right steps to prepare, respond, and recover.

A property may be at risk from more than one type of flooding.

River flooding (fluvial flooding)

River flooding occurs when rivers, streams, or brooks overflow their banks.

This usually happens after:

Prolonged or heavy rainfall
Water taking time to drain from upstream areas

River flooding can develop gradually, but once rivers overtop, water levels can rise quickly and remain high for hours or days.

Key features:

Often affects properties near rivers or watercourses
Can be forecast in advance
Floodwater may be deep and fast moving

Surface water flooding (pluvial flooding)

Surface water flooding happens when rainfall cannot drain away quickly enough.

This can occur when:

Rainfall is very heavy
Drains or sewers are overwhelmed
Ground surfaces are hard or heavily built over

Surface water flooding can happen almost anywhere, not just near rivers, and often occurs with little or no warning.

Key features:

Often sudden and unpredictable
May affect roads, gardens, and properties
Common in urban areas

Groundwater flooding

Groundwater flooding occurs when water levels in the ground rise above the surface.

This type of flooding typically happens:

After prolonged periods of rainfall
In areas with chalk, limestone, or permeable rock

Groundwater flooding can affect basements, cellars, and low‑lying areas and may last for weeks or even months.

Key features:

Slow to rise but slow to recede
Hard to prevent once it begins
Often seasonal

Sewer flooding (foul flooding)

Sewer flooding happens when sewer systems become overloaded and cannot cope with the volume of water.

This may occur during:

Heavy rainfall
Blockages or system failures

Sewer flooding can involve contaminated water, which presents additional health risks.

Key features:

Water may come up through toilets, sinks, or drains
Can cause significant disruption
Requires careful clean‑up and hygiene measures

Coastal flooding (tidal flooding)

Coastal flooding occurs when sea water floods land normally above the high‑tide level.

This can be caused by:

Storm surges
High tides combined with strong winds
Sea level rise

Coastal flooding can be severe and fast moving, particularly during storms.

Key features:

Often linked to weather conditions and tides
May affect large areas at once
Floodwater is salty and corrosive

Flash flooding

Flash flooding describes flooding that happens very quickly, often within minutes or hours.

It can be caused by:

Intense rainfall
Rapid surface water build‑up
Sudden watercourse overflow

Flash flooding can be particularly dangerous because of the speed at which it develops.

Key features:

Little or no warning
Water rises rapidly
Can be life‑threatening

Flooding from reservoirs or infrastructure failure

Flooding can also result from the failure of man‑made structures such as:

Reservoirs
Dams
Canals

While uncommon, this type of flooding can have serious consequences.

Key features:

Rare but potentially severe
Emergency plans are usually in place
Warning systems may operate in advance

More than one flood risk

Many properties are at risk from multiple types of flooding. For example, a home may be affected by both river flooding and surface water flooding.

Understanding your flood risk can help you:

Prepare a flood plan
Consider suitable protection or resilience measures
Know where to seek warnings and advice

Who is responsible for what?

Flood risk management in England and Wales involves several organisations working together. Under the Flood and Water Management Act 2010, all flood risk management authorities have a duty to cooperate and share information.

A quick guide

Environment Agency (England) – Manages flood risk from main rivers, reservoirs, estuaries, and the sea.
Natural Resources Wales – Manages flood risk from main rivers, reservoirs, estuaries, and the sea in Wales.
Lead Local Flood Authorities (usually Local Council) – Manage surface water, groundwater, and ordinary watercourses.
Planning Authorities - Planning authorities prepare Local Plans and decide planning applications, shaping how places develop. Communities can influence this through Neighbourhood Plans.
Internal Drainage Boards (IDBs) - are independent public bodies responsible for water level management in low lying areas (approximately 10% of England at present), working in partnership with other authorities.
Water and sewerage companies – Responsible for public sewers and piped water systems.
Highway authorities – Manage roadside ditches and highway drainage.
Property owners – Responsible for protecting their property and maintaining private drains within their boundary.

Are you a riparian owner?

If you own land or property next to a river, stream, or ditch, you are known as a riparian owner. You have the right to protect your property from flooding, but you also have responsibilities to maintain the watercourse so you do not increase flood risk for others. Environment Agency website has further guidence.

Taking the next step

You do not have to deal with flood risk alone. Whether you need help understanding flood maps or advice on making your home more resilient, support is available.

National Flood Forum Helpline: 01299 403 055

Flood warnings (Floodline) England and Wales: 0345 988 1188

Understanding your flood risk is not about being afraid – it is about being prepared. A simple flood plan today can make all the difference tomorrow.

Links to external websites are provided for information only. The National Flood Forum is not responsible for the content or availability of external sites and does not endorse any external organisations, services, or advice.