Types of flood

Floods can be caused by a number of factors, not just rivers and the sea.

The information below is a guide to the different types of flooding, their causes and the organisations responsible for managing them.

Surface runoff

Surface runoff is rainwater (this can also include melted snow) that collects on the surface of the ground rather than being absorbed into it or flowing into nearby rivers, streams or drains. It can be still or flowing along the ground. Very heavy rainfall can cause this type of flooding very quickly.

The organisations which are responsible for the prevention and treatment of surface runoff flooding are:

Lead local flood authority (Norfolk County Council)
Local planning authorities (your local district council)
Water utilities companies
Highways authorities
Riparian owners (owners of land next to a river, stream or ditch)

Tidal flooding

Many parts of Norfolk are at risk of flooding from rivers and the sea.

Coastal flooding – occurs when coastal defences are unable to contain the normal predicted high tides that can cause flooding. This can be made worse when a high tide combines with a storm surge (which is created by high winds or a deep atmospheric depression).

In addition, the tidal reaches of rivers in the Broads are particularly susceptible to high tides, especially when high water affects the ability of fresh water to drain to the sea, or salt water is forced deeper into fluvial systems.

River (fluvial) flooding

River flooding occurs as a result of water overflowing from river channels. This is influenced by two key factors:

The level of rainfall
The capacity of the ground and rivers to absorb and transport the water

The Environment Agency lead the management of flood and coastal risk from main rivers and the sea in England and Wales.

They have a flood information service that provides real time updates on the current risk of tidal and fluvial flooding.

You can also check to see if your property is at risk of tidal or fluvial flooding by visiting the Environment Agency website.

Ordinary watercourses

Ordinary watercourses are rivers, streams, ditches, drains, cuts, dykes, sluices, sewers (other than a public sewer) and passages through which water flows and which does not form part of a main river.

In Norfolk there are roughly 7,178 km of mapped ordinary watercourses that are included in the Environment Agency’s Detailed River Network. However because many watercourses are unmapped the real figure is likely to be higher.

The organisations responsible for managing this type of flood risk are:

Internal drainage boards
Local district councils
Riparian owners

Groundwater

Groundwater is water below the surface of the ground and in direct contact with the ground or subsoil, not including water in buried pipes or other containers.

Groundwater flooding happens as a result of water rising up from the underlying rocks or from water flowing from abnormal springs.

Flooding from groundwater is classed as a 'local flood risk' and is the responsibility of the lead local flood authority - Norfolk County Council.