Richmond Upon Thames - LP21 Flood Risk and Sustainable Drainage

Policy information sourced from Richmond Upon Thames Local Plan

LP 21 Flood Risk and Sustainable Drainage

All developments should avoid, or minimise, contributing to all sources of flooding, including fluvial, tidal, surface water, groundwater and flooding from sewers, taking account of climate change and without increasing flood risk elsewhere. Development will be guided to areas of lower risk by applying the ‘Sequential Test’ as set out in national policy guidance, and where necessary, the ‘Exception Test’ will be applied. Unacceptable developments and land uses will be refused in line with national policy and guidance, the Council’s Strategic Flood Risk Assessment (SFRA) and as outlined in the table below.

In Flood Zones 2 and 3, all proposals on sites of 10 dwellings or more or 1000sqm of non-residential development or more, or on any other proposal where safe access/egress cannot be achieved, a Flood Emergency Plan must be submitted.

Where a Flood Risk Assessment is required, on-site attenuation to alleviate fluvial and/or surface water flooding over and above the Environment Agency’s floodplain compensation is required where feasible.

Land uses and developments – restrictions	Sequential Test	Exception Test	Flood Risk Assessment
Zone 3b	The functional floodplain as identified in the Council’s Strategic Flood Risk Assessment will be protected by not permitting any form of development on undeveloped sites unless it: is for Water Compatible development; is for essential utility infrastructure which has to be located in a flood risk area and no alternative locations are available and it can be demonstrated that the development would be safe, without increasing flood risk elsewhere and where possible would reduce flood risk overall. Redevelopment of existing developed sites will only be supported if there is no intensification of the land use and a net flood risk reduction is proposed; any restoration of the functional floodplain will be supported. Proposals for the change of use or conversion to a use with a higher vulnerability classification will not be permitted.	Required for essential utility infrastructure	Required for essential utility infrastructure	Required for all development proposals
Zone 3a	Land uses are restricted to Water Compatible, Less Vulnerable and More Vulnerable development. Highly Vulnerable developments will not be permitted. Self-contained residential basements and bedrooms at basement level will not be permitted.	Required for all developments unless exceptions outlined in the justification apply	Required for more vulnerable development	Required for all development proposals
Zone 2	No land use restrictions Self-contained residential basements and bedrooms at basement level will not be permitted.	Required for all developments unless exceptions outlined in the justification apply	Required for highly vulnerable development	Required for all development proposals unless for change of use from water compatible to less vulnerable
Zone 1	No land use restrictions	Not applicable	Not applicable	A Drainage Statement is required for sites all major developments. Required for all other development proposals where there is evidence of a risk from other sources of flooding, including surface water, ground water and sewer flooding.

Basements and subterranean developments

Basements within flood affected areas of the borough represent a particularly high risk to life, as they may be subject to very rapid inundation. Applicants will have to demonstrate that their proposal complies with the following:

Flood Zone 3b (Functional Floodplain)	Basements, basement extensions, conversions of basements to a higher vulnerability classification or self-contained units will not be permitted.
Flood Zone 3a (Tidal / Fluvial)	In areas of Extreme, Significant and Moderate Breach Hazard (as set out in the Council’s SFRA): New basements: a. restricted to Less Vulnerable / Water Compatible use only. b. ‘More Vulnerable’ uses will only be considered if a site-specific Flood Risk Assessment demonstrates that the risk to life can be managed. Bedrooms at basement levels will not be permitted. c. ‘Highly Vulnerable’ such as self-contained basements/bedrooms uses will not be permitted. Existing basements: a. No basement extensions, conversions or additions for ‘Highly Vulnerable’ uses. b. ‘More Vulnerable’ uses will only be considered if a site-specific Flood Risk Assessment demonstrates that the risk to life can be managed. In areas of Low or No Breach Hazard (as set out in the Council’s SFRA): New basements: if the Exception Test (where applicable) is passed, basements may be permitted for residential use where they are not self-contained or used for bedrooms. Existing basements: basement extensions, conversions or additions may be permitted for existing developments where they are not self-contained or used for bedrooms. If a basement, basement extension or conversion is acceptable in principle in terms of its location, it must have internal access to a higher floor and flood resistant and resilient design techniques must be adopted.
Flood Zone 2	In areas of Extreme, Significant and Moderate Breach Hazard (as set out in the Council’s SFRA): New Basements: if the Exception Test (where applicable) is passed, basements may be permitted for residential use where they are not self-contained or used for bedrooms. Existing Basements: basement extensions, conversions or additions maybe permitted for existing developments where they are not self-contained or used for bedrooms If a basement, basement extension or conversion is acceptable in principle in terms of its location, it must have internal access to a higher floor and flood resistant and resilient design techniques must be adopted
Flood Zone 1	No restrictions on new or extensions to existing basements

Flood Zone 3b (Functional Floodplain)

Basements, basement extensions, conversions of basements to a higher vulnerability classification or self-contained units will not be permitted.

Flood Zone 3a (Tidal / Fluvial)

In areas of Extreme, Significant and Moderate Breach Hazard (as set out in the Council’s SFRA):

New basements:
a. restricted to Less Vulnerable / Water Compatible use only.
b. ‘More Vulnerable’ uses will only be considered if a site-specific Flood Risk Assessment
demonstrates that the risk to life can be managed. Bedrooms at basement levels will not be
permitted.
c. ‘Highly Vulnerable’ such as self-contained basements/bedrooms uses will not be permitted.
Existing basements:
a. No basement extensions, conversions or additions for ‘Highly Vulnerable’ uses.
b. ‘More Vulnerable’ uses will only be considered if a site-specific Flood Risk Assessment
demonstrates that the risk to life can be managed.

In areas of Low or No Breach Hazard (as set out in the Council’s SFRA):

New basements: if the Exception Test (where applicable) is passed, basements may be permitted for residential use where they are not self-contained or used for bedrooms.
Existing basements: basement extensions, conversions or additions may be permitted for existing developments where they are not self-contained or used for bedrooms.

If a basement, basement extension or conversion is acceptable in principle in terms of its location, it must have internal access to a higher floor and flood resistant and resilient design techniques must be adopted.

Flood Zone 2

In areas of Extreme, Significant and Moderate Breach Hazard (as set out in the Council’s SFRA): New Basements: if the Exception Test (where applicable) is passed, basements may be permitted for residential use where they are not self-contained or used for bedrooms.
Existing Basements: basement extensions, conversions or additions maybe permitted for existing developments where they are not self-contained or used for bedrooms If a basement, basement extension or conversion is acceptable in principle in terms of its location, it must have internal access to a higher floor and flood resistant and resilient design techniques must be adopted

Flood Zone 1

No restrictions on new or extensions to existing basements

Sustainable drainage

The Council will require the use of Sustainable Drainage Systems (SuDS) in all development proposals. Applicants will have to demonstrate that their proposal complies with the following:

A reduction in surface water discharge to greenfield run-off rates wherever feasible.
Where greenfield run-off rates are not feasible, this will need to be demonstrated by the applicant, and in such instances, the minimum requirement is to achieve at least a 50% attenuation of the site’s surface water runoff at peak times based on the levels existing prior to the development.

Flood defences

Applicants will have to demonstrate that their proposal complies with the following:

Retain the effectiveness, stability and integrity of flood defences, river banks and other formal and informal flood defence infrastructure.
Ensure the proposal does not prevent essential maintenance and upgrading to be carried out in the future.
Set back developments from river banks and existing flood defence infrastructure where possible (16 metres for the tidal Thames and 8 metres for other rivers).
Take into account the requirements of the Thames Estuary 2100 Plan and the River Thames Scheme, and demonstrate how the current and future requirements for flood defences have been incorporated into the development.
The removal of formal or informal flood defences is not acceptable unless this is part of an agreed flood risk management strategy by the Environment Agency.

For more information please see the Local Plan