This policy requires all new developments to manage flood risk, considering climate change and avoiding increased risk elsewhere. For areas at higher risk of flooding (Zones 2 and 3a), a 'Sequential Test' and potentially an 'Exception Test' are needed to ensure development is appropriate. Specific rules apply to different flood zones, restricting certain land uses and requiring measures like raised floor levels and safe access/egress.
Plain-English summary of the adopted policy text below. The full text is the rule; this is the gist.
Flood Risk Management
A. All planning applications will need to clearly demonstrate that the proposals avoid, minimise, or reduce contributing to all sources of flooding, including fluvial, tidal, surface water, groundwater, flooding from sewers, take account of climate change (including predicted future changes), and would not increase flood risk elsewhere.
The application of Sequential Test
B. Future development in Zone 3a and Zone 2 will only be considered if the 'Sequential Test' has been applied and the Exceptions Test passed in accordance with national planning policy and guidance. The Sequential Test is considered to have been passed, and a Flood Risk Assessment will not be required, if the proposal is not a major development or at least one of the following applies:
1. The application site is located within an Area Strategy area as identified in this Local Plan; including within a 400m buffer around the Town Centre based strategies*:
a. Vauxhall Nine Elms Battersea Opportunity Area (including Battersea Design and Technology quarter)
b. Roehampton Regeneration Area
c. The Wandle Valley
d. Wandsworth’ s Riverside
e. Balham*
f. Clapham Junction and York Road/Winstanley Regeneration Area*
g. Putney*
h. Tooting*
i. Wandsworth Town, including the Wandle Delta sub-area*
2. The application site is a Local Plan Site Allocation, unless the proposed use is not in accordance with the allocations of the Local Plan.
3. Redevelopment of an existing single residential property or its ancillary uses.
4. Minor development, conversions and change of use.
5. For development sites falling outside of these areas, the default area of search for the Sequential Test to be applied will be the borough administrative area, unless justification is provided for a smaller area as described in the Strategic Flood Risk Assessment.
C. Development will be guided to areas of lower risk, both on-site and by applying the 'Sequential Test' as set out in national policy guidance, and where required, the 'Exception Test'. Inappropriate developments and land uses will be refused in accordance with national policy and guidance, and the Council's Strategic Flood Risk Assessment (SFRA). In flood zones 2 and 3, all planning applications (or other relevant applications) on sites of 10 or more dwellings 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 solutions to alleviate fluvial and/or surface water flooding over and above floodplain compensation is required. The consideration of potential increases in flood risk off-site where development would result in a loss of floodplain storage is also required with suitable mitigation proposed in accordance with the advice of the Environment Agency and Lead Local Flood Authority.
Flood Zone Land uses and development - Sequential Exception Flood Risk restrictions Test Test Assessment
Zone 3b The functional floodplain as identified in Required for Required for Required for the Council’s SFRA will be protected by essential essential all not permitting any form of development infrastructure infrastructure development on undeveloped sites unless it: proposals
is for Water Compatible development; is for essential 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 operational and safe, result in no net loss of flood storage, not impede water flows, not increase 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 a change of use or conversion to a use with a higher vulnerability classification will not be permitted.
To provide safe refuge, and depending on location, finished floor levels for all development must be raised to a minimum of 300mm above the 1 in 100 fluvial level inclusive of an allowance for climate change, or an appropriate extreme water level as advised by the Environment Agency for defended tidal areas. Safe access and egress at a Low Hazard rating is required.
Zone 3a Land uses are restricted to: Required for Required for Required for (Tidal/Fluvial) all more all Essential Infrastructure; developments vulnerable development Water Compatible; unless development proposals Less Vulnerable; and exceptions More Vulnerable development outlined in
Flood Zone Land uses and development - Sequential Exception Flood Risk restrictions Test Test Assessment
Highly Vulnerable developments will not the be permitted. supporting text apply To provide safe refuge, and depending on location, finished floor levels for all development must be raised to a minimum of 300mm above the 1 in 100 fluvial level inclusive of an allowance for climate change, or an appropriate extreme water level as advised by the Environment Agency for defended tidal areas. Safe access and egress at a Low Hazard rating is required.
Self-contained residential basements will not be permitted in locations at risk of fluvial, or tidal defended flooding.
Bedrooms at basement level will not be permitted in fluvial flood risk areas subject to the requirements set out in Table 15.2
Zone 2 No land use restrictions. Required for Required for Required for all highly all To provide safe refuge, and depending on developments vulnerable development location, finished floor levels for less and unless development proposals more vulnerable development must be exceptions unless for raised to a minimum of 300mm above outlined in change of use the 1 in 100 fluvial level inclusive of an the from water allowance for climate change, or an supporting compatible to appropriate extreme water level as text apply less advised by the Environment Agency for vulnerable defended tidal areas. Safe access and egress at a Low Hazard rating is required.
Self-contained residential basements will not be permitted in locations at risk of fluvial, or tidal defended flooding.
Bedrooms at basement level will not be permitted in fluvial flood risk areas subject to the requirements set out in Table 15.2
Flood Zone Land uses and development - Sequential Exception Flood Risk restrictions Test Test Assessment
Zone 1 No land use restrictions. Not Not A sustainable applicable applicable Drainage Where development over 1 ha is Statement is proposed or there is evidence of flooding required for from another localised source all major opportunities should be sought to: development.
Ensure that the management of Where surface water runoff from the site development is considered early in the site over 1 ha is planning and design process; proposed or Ensure that proposals achieve an for all other overall reduction in the level of development flood risk to the surrounding area, proposals through the appropriate application where there of sustainable drainage techniques. is evidence of a risk from other sources of flooding, including surface water, groundwater and sewer flooding.
Table 15.1 Flood Zones - Development Restrictions
Basements and Subterranean Developments
D. 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 Basements, basement extensions, conversions of basements to a higher vulnerability 3b classification or self-contained units will not be permitted.
Flood Zone In areas of Extreme, Significant and Moderate Breach Hazard (as set out in the 3a Council's SFRA):
New basements:
Restricted to Less Vulnerable / Water Compatible use only. ‘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. ‘Highly Vulnerable’ uses such as self-contained basements/bedrooms will not be permitted.
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, in locations at risk of fluvial flooding, are not used for bedrooms.
If a basement, basement extension or conversion is acceptable in principle in terms of its location, it must:
have safe access threshold levels and internal staircases provided to access floors to a minimum of 300mm above the 1 in 100 fluvial level inclusive of an allowance for climate change, or an appropriate extreme water level as advised by the Environment Agency for defended tidal areas. The only exception to this is for basement development within areas of defended tidal flood risk, where the applicant has demonstrated that a permanent fixed barrier is in place to prevent floodwater from entering any sleeping accommodation that is located below the extreme water level in accordance with the hazard advice above. Flood resistant and resilient design techniques must be adopted.
In areas at risk of surface water flooding, basements, basement extensions and basement conversions must be protected by appropriate mitigation such as raising floor level thresholds, providing storage for surface water or other SuDS proposal. Basements will not be permitted in areas of high surface water risk without appropriate mitigation.
Flood Zone In areas of Extreme, Significant and Moderate Breach Hazard (as set out in the 2 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, in locations at risk of fluvial flooding, are not used for bedrooms.
Existing Basements:
Basement extensions, conversions or additions maybe permitted for existing developments where they are not self-contained or, in locations at risk of fluvial flooding, are not used for bedrooms.
If a basement, basement extension or conversion is acceptable in principle in terms of its location, it must:
have safe access threshold levels and internal staircases provided to access floors to a minimum of 300mm above the 1 in 100 fluvial level inclusive of an allowance for climate change, or an appropriate extreme water level as advised by the Environment Agency for defended tidal areas. The only exception to this is for basement development within areas of defended tidal flood risk, where the applicant has demonstrated that a permanent fixed barrier is in place to prevent floodwater from entering any sleeping accommodation that is located below the extreme water level in accordance with the hazard advice above. Flood resistant and resilient design techniques must be adopted.
In areas at risk of surface water flooding, basements, basement extensions and basement conversions must be protected by appropriate mitigation such as raising floor level thresholds, providing storage for surface water or other SuDS proposal. Basements will not be permitted in areas of high surface water risk without appropriate mitigation.
Flood Zone In areas at risk of surface water flooding, basements, basement extensions and basement 1 conversions must be protected by appropriate mitigation such as raising floor level thresholds, providing storage for surface water or other SuDS proposal.
Table 15.2 Requirements for Basements in Flood Zones
Sustainable Drainage
E. The Council will require the use of Sustainable Drainage Systems (SuDS) in all development proposals.
Applicants will have to demonstrate that:
1. A reduction in surface water discharge to greenfield run-off rates will be achieved unless it is clearly demonstrated that this is technically unfeasible.
2. Where it has been clearly demonstrated that greenfield run-off rates are not technically feasible, at least a 50% attenuation will be required, with an objective of achieving 100% attenuation of the existing (undeveloped) site's surface water runoff at peak times based on the levels existing prior to the commencement of development.
3. There should be no loss of flood storage in areas affected by fluvial flooding and any increase in built footprint within the fluvial 1 in 100 (inclusive of climate change allowance) flood extent must be compensated for on a level for level, volume for volume basis.
4. Where minor development is proposed, schemes should not affect floodplain storage or flow routes through the incorporation of mitigation measures in line with the Construction Industry Research and Information Association’s guidance on SuDS.
F. The Council will require, where necessary, financial contributions through a S106 planning obligation towards flood protection measures and SuDS in accordance with the Council’s Planning Obligations SPD or successor document.
G. Applicants must demonstrate that surface water must be drained to ground water courses or a surface water sewer and not to the foul water sewer.
Flood Defences
H. Applicants will be required to demonstrate, where relevant, that their proposal complies with the following:
1. That the effectiveness, stability and integrity of flood defences, river banks and other formal and informal flood defence infrastructure will not be compromised.
2. Ensures that the proposal does not prevent essential maintenance and upgrading of any formal or informal flood defence infrastructure to be carried out in the future in a cost-effective manner in agreement with the Environment Agency.
3. That any physical structures are set back from river banks and existing flood defence infrastructure unless it can be clearly demonstrated that the effectiveness of such infrastructure would not be compromised (the distances being 16 metres for the tidal Thames and 8 metres for other rivers including those culverted).
4. Has taken into account the requirements of the Environment Agency’s Thames Estuary 2100 Plan, and demonstrates how current and future requirements for flood defences have been incorporated into the development, including the need to raise flood defences to the required levels whilst enhancing the riverside environment in accordance with the Thames Estuary 2100 Plan.
5. Would not result in the removal of formal or informal flood defences unless this forms part of an agreed flood risk management strategy adopted or approved by the Environment Agency.
6. That the opportunities to undertake river restoration and enhancement and implement natural flood management measures as part of a development to make space for water have been assessed and where technically feasible incorporated into the proposal. Enhancement of existing assets, such as
through de-culverting, the using bio-engineered river walls, and raising bridge soffits to take into account climate change should be accommodated in development proposals where technically feasible.
7. Culverting of water courses and building over culverts will be resisted unless it can be clearly demonstrated that such approaches are necessary in order to achieve the delivery of development.
Deculverting is encouraged where possible.
Multifunctional Benefits
I. In addressing flood mitigation opportunities to bring other benefits including recreational, habitat creation to support biodiversity and urban greening will be encouraged.