Draft Flood Risk Supplementary Planning Document




1D Hydraulic Model

Hydraulic model which computes flow in a single dimension, suitable for representing systems with a defined flow direction such as river channels, pipes and culverts

2D Hydraulic Model

Hydraulic model which computes flow in multiple dimensions, suitable for representing systems without a defined flow direction including topographic surfaces such as floodplains

Asset Information Management System (AIMS)

Environment Agency database of assets associated with Main Rivers including defences, structures and channel types. Information regarding location, standard of service, dimensions and condition.


In the context of this report - the storing of water to reduce peak discharge of water.

Catchment Flood Management Plan

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

Climate Change

Long term variations in global temperature and weather patterns caused by natural and human actions. For fluvial events a 20% increase in river flow is applied and for rainfall events, a 30% increase. These climate change values are based upon information within the NPPF and Planning Practice Guidance.


A channel or pipe that carries water below the level of the ground.

DG5 Register

A water-company held register of properties which have experienced sewer flooding due to hydraulic overload, or properties which are 'at risk' of sewer flooding more frequently than once in 20 years.

Exception Test

The Exception Test should be applied following the application of the Sequential Test. Conditions need to be met before the exception test can be applied.

Flood Defence

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

Flood Resilience

Measures that minimise water ingress and promote fast drying and easy cleaning, to prevent any permanent damage.

Flood Resistance

Measures to prevent flood water entering a building or damaging its fabric.  This has the same meaning as flood proof.

Flood Risk

The level of flood risk is the product of the frequency or likelihood of the flood events and their consequences (such as loss, damage, harm, distress and disruption).

Flood Zone

Flood Zones show the probability of flooding, ignoring the presence of existing defences

Functional Floodplain

Land where water has to flow or be stored in times of flood.


Water that is in the ground, this is usually referring to water in the saturated zone below the water table.

Lead Local Flood Authority (LLFA)

As defined by the Flood and Water Management Act, in relation to an area in England, this means the unitary authority or where there is no unitary authority, the county council for the area, in this case Surrey County Council.

Light Detection and Ranging (LiDAR)

Airborne ground survey mapping technique, which uses a laser to measure the distance between the aircraft and the ground.

Local Planning Authority (LPA)

Body that is responsible for controlling planning and development through the planning system.

Main River

Watercourse defined on a 'Main River Map' designated by Defra. The Environment Agency has permissive powers to carry out flood defence works, maintenance and operational activities for Main Rivers only.

Mitigation measures

An element of development design which may be used to manage flood risk or avoid an increase in flood risk elsewhere.

Ordinary Watercourse

A watercourse that does not form part of a Main River. This includes "all rivers and streams and all ditches, drains, cuts, culverts, dikes, sluices (other than public sewers within the meaning of the Water Industry Act 1991) and passages, through which water flows" according to the Land Drainage Act 1991.

Ramsar Site

Wetlands of international importance, designated under the Ramsar Convention

Residual Flood Risk

The remaining flood risk after risk reduction measures have been taken into account.

Sequential Test

Aims to steer vulnerable development to areas of lowest flood risk.

Sewer Flooding

Flooding caused by a blockage or overflowing in a sewer or urban drainage system.

Surface Water

Flooding caused when intense rainfall exceeds the capacity of the drainage systems or when, during prolonged periods of wet weather, the soil is so saturated such that it cannot accept any more water.

Sustainable drainage systems (SuDS)

Methods of management practices and control structures that are designed to drain surface water in a more sustainable manner than some conventional techniques.

Topographic survey

A survey of ground levels.