Attenuation is the process of storing water on a site and slowly releasing it in a controlled way, either into the ground, to a surface water drain or a watercourse. This reduces how fast rainfall runs off a site, thereby reducing flood risk.


An area of land where surface water from rain, melting snow or ice converges to a single point at a lower elevation, usually a watercourse.

Catchment Flood Management Plan

A high-level planning strategy through which the Environment Agency works with their key decision makers within a river catchment to identify and agree policies to secure the long-term sustainable management of flood risk.

Close proximity

Where it is reasonable to assume that the affected properties were flooded from the same source (or a combination of sources, such as surface water and groundwater acting together).


A culvert is a structure or pipe that allows water to flow underground in order to avoid an obstruction, such as a road or railway. Historically, culverts have even been used to divert watercourses under new housing developments. Culverts can take a number of forms, such as plastic pipes, brick-lined tunnels or concrete structures, and may be used to form a bridge-like structure to carry traffic. Generally, where culverts form part of a watercourse, they will be the responsibility of the Riparian Owner to maintain.


Designation is a form of legal protection reserved for key structures or features that are privately owned and maintained and that contribute to the management of flood risk. The aim of designation is to ensure that the owners do not inadvertently alter these structures and potentially increase flood risk to themselves, their neighbours and the wider community. A designation is a legally binding notice served on the owner of the structure or feature. It is also a local land charge meaning that the designation will carry onto successive owners or occupiers of the land.

Flood Asset

Flood Assets are any structures or features that could have an effect on flood risk. These could be pumping stations, flood defence banks and walls, weirs, culverts and pipes, ditches and drains.

Flood Defence

Infrastructure used to protect an area against floods such as floodwalls and embankments; they are designed to a specific standard of protection.

Flood Resilience

Actions taken which allow the entry of flood water through a property, but enable swift recovery after the flood event. Flood resilience measures may include (among others) flood-resistant construction materials, raised electricity sockets and water-resistant flooring.

Flood Resistance

Actions taken to prevent the entry of flood water to a property. Flood resistance measures may include flood barriers placed over doorways.

Flood Risk Management Authority

Includes the Environment Agency, a lead local flood authority, a district council for an area for which there is no unitary authority, an internal drainage board, a water company and a highway authority.

Flood Zones

Nationally consistent boundary of ‘high’ and ‘medium’ flood risk, published on a quarterly basis by the Environment Agency. These can be viewed on our Flood Risk Map under the Flood Map for Planning.


The processes associated with rivers and streams and the deposits and landforms created by them.

Internal Drainage Board

An Internal Drainage Board (IDB) is a local public authority established in areas of special drainage need in England and Wales. They have permissive powers to manage water levels within their respective drainage districts. IDBs undertake works to reduce flood risk to people and property and manage water levels to meet local needs.

Internal flooding

Where floodwater has crossed the threshold of a commercial or residential building.