Policy information sourced from the Merton Sites and Policies Plan
DM F1 Support for flood risk management
Link to Core Planning Strategy Policy CS 16 Flood Risk Management
Policy aim
To mitigate the impact of flooding in Merton, in line with the National Planning Policy Framework (NPPF 2012) and associated national guidance, the Flood and Water Management Act 2010, Flood Risk Regulations 2009, The Water Framework Directive, the council’s duty as Lead Local Flood Authority and Merton’s Local Flood Risk Management Strategy.
Policy
- To minimise the impact of flooding in the borough the council will:
- Encourage development to locate in areas of lower risk by applying the Sequential Test; any unacceptable development and land uses will not be permitted.
- Ensure that flood resilient and resistant measures are incorporated into design of development proposals in any area susceptible to flooding to minimise and manage the risk of flooding.
- Ensure that developments consider all sources of flooding from fluvial, groundwater, surface water run off, ordinary watercourse, and sewer; and including the risks of flooding arising from and to the development.
- All development proposals must have regard to the Strategic Flood Risk Assessment (SFRA) and the Local Flood Risk Management Strategy.
- Permit appropriate development in Flood Zones 1, 2, 3a and 3b subject to meeting the criteria in the following table:
| Flood Zones | Sequential Test | Exception Test | Flood risk assessment |
|---|---|---|---|
| Flood Zone 1 Low Risk: This zone has 1 in 1000 or less annual probability of fluvial flooding or less (<0.1%) in any year. No land development restrictions. (Except for areas that have been identified as having critical drainage problems by the Environment Agency). | Not applicable. (Except for areas that are within a Critical Drainage Area). | Not applicable. | Required for sites greater than 1 ha or other developments proposals where there is evidence of risk from other sources of flooding including surface water, groundwater, ordinary watercourses and sewer flooding. |
| Flood Zone 2 Medium Risk: This zone has between 1 in 100 and 1 in 1000 annual probability of fluvial flooding (between 1% and 0.1%). In this zone self-contained residential units at basement level and bedrooms at basement level will not be permitted by the council without appropriate mitigation measures in line with Environment Agency guidance. All basement, basement conversions and basement extensions must: • have access and escape routes to a higher floor, including other emergency planning measures; and, • adopt flood resilient and resistant design techniques. Flooding from all sources (including surface and groundwater flooding) should be considered, where basements are proposed they must have mitigation measures as part of the development proposal and design layout to reduce the risk of flooding to and from the development and surrounding area. | Required for all developments (including minor development and change of use). | Required for developments classed as ‘highly vulnerable’. | Required for all development proposals unless the development is for change of use from ‘water compatible’ to ‘less vulnerable’ classification development. |
| Flood Zone 3a High Risk: This zone has 1 in 100 annual probability or greater (>1%) of fluvial flooding. Development proposals are constrained to ‘water compatible’, ‘less vulnerable’ and ‘more vulnerable’ classification. Development classed as ‘Highly vulnerable’ will not be permitted by the council in line with Environment Agency guidance. | Required for all developments. | Required for developments classed as ‘more vulnerable’ and ‘essential infrastructure.’ | Required for all development proposals. |
| Residential basements: Self-contained residential basement and bedrooms at basement level will not be permitted by the council. All other basement, basement conversion and basement extensions must: • have access and escape routes to a higher floor, including other emergency planning measures; if an appropriate escape route can not be provided then the basement proposal will not be permitted and • adopt appropriate resilient design techniques and appropriate flood mitigation measures. | N/A | N/A | N/A |
| Flood Zone 3b The functional floodplain will be protected by not allowing any form of development on undeveloped sites unless it is: • classed as ‘water compatible’ • For development of ‘essential infrastructure’ which has to be located in a flood risk area and where no alternative locations are available, should be developed safely, without increasing flood risk elsewhere and where possible reduce the flood risk overall. The council will only support redevelopment of existing developed sites if there is no greater flood risk than currently exists to the re-development or wider community. In accordance with the NPPF if, following the application of the Sequential Test, it is not possible, consistent with the wider sustainability objectives, for development to be located in flood zones with lower probability of flooding: • The developer must demonstrate that the development provides a wider social, environment, and economical benefit to the wider community that outweighs the flood risk, as informed by the SFRA and, • Submit a site specific flood risk assessment which must demonstrate that the development will be safe for the life time of the build taking into account vulnerability of it users, without increasing the risk to the development and surrounding area; and where possible will reduce flood risk overall. | Required for developments classed as ‘essential infrastructure’. | Required for developments classed as ‘essential infrastructure’. | Required for all development. |
| Basements, basement extensions and conversion of basements to a ‘higher vulnerability’ classification or self-contained units will not be permitted by the council. | N/A | N/A | N/A |
For more information see the Merton Sites and Policies Plan