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.

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.

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 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.

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

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.

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

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.

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.

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.

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

The Lead Local Flood Authority in Oxfordshire is Oxfordshire County Council.

Main rivers are a statutory type of watercourse in England and Wales and are usually larger streams and rivers. A main river is defined as such on the Environment Agency’s Main River map, and can include any structure or appliance for controlling or regulating the flow of water in, into or out of a main river. The Environment Agency’s powers to carry out flood defence works apply to Main Rivers only. See our Flood Risk Map for a list of all Oxfordshire main rivers.

The National Planning Policy Framework sets out government’s planning policies for England and how these are expected to be applied. The framework acts as guidance for local planning authorities and decision-takers, both in drawing up plans and making decisions about planning applications.

Any watercourse not defined by the Environment Agency as a main river. Ordinary watercourses are generally smaller than main rivers, and can include streams, ditches and piped watercourses. See our Flood Risk Map for a map of all Oxfordshire main rivers.

The Preliminary Flood Risk Assessment (PFRA) provides an overview of past floods and the possible harmful consequences of future floods, leading to the identification of Areas of Significant Risk. The floods to be included are those which had significant harmful consequences for human health, economic activity or the environment (including cultural heritage), or which would have significant harmful consequences for those matters if they were to occur now.

Residual risks are those remaining after actions have been taken to mitigate or defend against flood risk. Examples of residual flood risk include: the failure of flood management infrastructure such as a breach of a raised flood defence, blockage of a surface water conveyance system, overtopping of an upstream storage area, or failure of a pumped drainage system; failure of a reservoir; or a severe flood event that exceeds a flood management design standard, such as a flood that overtops a raised flood defence, or an intense rainfall event which the drainage system cannot cope with.

All landowners and tenants whose property has a watercourse within or adjacent to the boundaries of their land, are riparian owners of that watercourse. Riparian owners have a responsibility for maintaining the watercourse and bank, clearing debris and keeping any ditches or structures clear. This ownership extends to watercourses that are piped (culverted) under the land.

A sewer is a pipe which carries and removes either rainwater (surface water runoff), foul water (from toilets, sinks etc) or a combination of both. A sewer can be categorised as either a private or public sewer. A private sewer is solely the responsibility of the occupiers/owners of the properties that it serves. A public sewer is a sewer that has been adopted and maintained by a Sewerage Undertaker.

Strategic Flood Risk Assessments (SFRAs) are studies carried out by one or more local planning authorities to assess the risk to an area from flooding from all sources, now and in the future. An SFRA takes into account the impacts of climate change and assesses the impact that land use changes and development in the area will have on flood risk. They are background evidence-based documents which inform the Local Development Framework.

A long-term action plan to manage surface water in an area and should influence future capital investment, drainage maintenance, public engagement and understanding, land-use planning, emergency planning and future developments.

Methods of management practices and control structures that are designed to drain surface water in a more sustainable manner than conventional techniques. These include permeable surfaces, swales, wetlands and ponds.

The Water Framework Directive was introduced in December 2000 and became UK law in December 2003. The directive focuses on improving the ecology of our water ecosystems and aims to protect and enhance the quality of surface water, groundwater, estuaries and coastal waters. The Environment Agency are the lead authority responsible for the delivery of these targets, but must work closely with lead local flood authorities, such as the County Council, to ensure that targets are achieved.

A watercourse is any channel through which water flows. The channel can be natural or man-made. It can be above or below ground and does not have to contain water all year round.

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