Policy information sourced from the Richmond Upon Thames Local Plan
Policy 8 Flood Risk and Sustainable Drainage (Strategic Policy)
A. All developments will need to be made safe for their lifetime and clearly demonstrate that they avoid or reduce contributing to all sources of flooding, including fluvial, tidal, surface water, groundwater and flooding from sewers; taking account of climate change and that they do not increase 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. A sequential approach should be taken to the layout of sites, locating development in areas at lowest risk from flooding on a site. Unacceptable developments and land uses will be refused in line with national policy, the requirements set out in the Council’s Strategic Flood Risk Assessment (SFRA) and as outlined in the table below.
B. To enable development, proposals must provide mitigation and resilience against flood risk as set out in the Council’s SFRA, including but not limited to adequately raising finished floor levels, providing flood storage compensation and alleviation. Advice should 202 Richmond upon Thames Local Plan Track Changes Version for Environment Committee Sep2025 be sought from the Lead Local Flood Authority (LLFA) and/or the Environment Agency as appropriate.
C. For all proposals on sites of 10 dwellings or more, or 1000sqm of non-residential development or more, in Flood Zones 2 and 3, or in areas at Risk of Flooding from Surface Water in a 1 in 100 year event or greater, or within a Surface Water Management Plan hotspot, or on any other proposal where safe access/egress cannot be achieved, a Flood Emergency Plan must be submitted.
D. Where a Flood Risk Assessment is required, appropriate measures to alleviate fluvial, undefended tidal and surface water flooding should be provided over and above the minimum flood storage compensation and on-site attenuation requirements, where feasible and justified by appropriate evidence.
E. Where possible, land within major development sites should be safeguarded for potential flood mitigation use through the active consideration of predicted flood mapping from all sources.
| Zone | Land use and development – 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 additional built development proposed within the undeveloped functional floodplain, no increase in vulnerability 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. | |||
| Zone 3a and areas at Risk of Flooding from Surface Water in a 1 in 100 year event. | 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 supporting text to this policy 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 supporting text to this policy apply | Required for highly vulnerable development | Required for all development 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 |
Throughflow and groundwater:
F. In line with the Council’s SFRA, the following catchment areas have been designated as throughflow and groundwater policy zones:
- Richmond Hill (Richmond)
- Strawberry Hill (Twickenham)
- Marble Hill (Twickenham)
- St Margarets West
G. Subsurface structure development proposals within these zones need to fulfil site-specific requirements to demonstrate that basements, cellars, and other subsurface structures can be safely developed without increasing throughflow and groundwater related flood risk.
Sustainable Drainage
H. The Council requires the use of Sustainable Drainage Systems (SuDS) in all development proposals to manage surface water runoff as close to its source as possible, using the most sustainable solutions to reduce runoff volumes and rates. Ideally, all surface water should be managed on site. The development must not increase flood risk elsewhere and where possible reduce flood risk overall. 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 runoff rate of 2 l/s or below 50% attenuation of the site’s surface water runoff at peak times based on the levels existing prior to the development will be achieved.
Flood defences:
I. Applicants will have to demonstrate that their proposals complies with the following:
- Retain the effectiveness, stability and integrity of flood defences, riverbanks and other formal and informal flood defence infrastructure.
- Ensure the proposal does not prevent essential maintenance and upgrading from being carried out in the future.
- Unless exceptional circumstances are demonstrated for not doing so, all development should be set back from riverbanks and existing flood defence infrastructure to allow for any foreseeable future maintenance and upgrades in a sustainable and cost effective way. This must be a minimum of 16 metres from the landward side of any tidal flood defences and 8 metres for other main rivers including culverted main rivers, although a greater set back may be required on some sites. Where the minimum requirements cannot be met, evidence to justify this must be submitted at planning application stage and agreed by the Environment Agency.
- 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. This includes ensuring that no new active flood defences are delivered as part of a development and that any developments coming forward that currently use active flood defences replace them with permanent flood defences.
- 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
J. In addition, in line with the requirements of the Thames Estuary 2100 Plan, developments adjoining the River Thames must maintain and where necessary enhance or raise (or demonstrate how they could be raised in the future) flood defences to the statutory level as set out in the TE2100 Plan (or latest version), demonstrating that they will continue to provide adequate flood protection for the lifetime of the development. In alignment with the Council’s SFRA, developments on the river should make the most of the opportunities presented by regeneration and redevelopment on river corridors to reduce fluvial flood risk through location, layout and design of development. Opportunities should also look at flood compatibility, flood resilience and maximising open space for flood water.
Basements in areas of Flood Risk:
K. Basements within flood affected areas of the borough represent a particularly elevated 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 where the basement is located | Guidance that developments should follow |
|---|---|
| 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:
• 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 |
| Through-flow and ground-water policy zones | Basement and cellar developments within these throughflow and groundwater policy zones must be confined to the curtilage of the site. In addition, they should not exceed a maximum of 50 percent of each garden or open space area of the site.
A Screening Assessment must be carried out for all basement and cellar proposals in the throughflow and groundwater policy zones. Information provided in the screening assessment should address the following areas:
a. Subterranean characteristics b. Land stability (including site slope) c. Flood risk and drainage (including throughflow, groundwater and surface water). If the proposed subsurface development may have an impact on the local environment, or if further investigation work is required, then a Basement Impact Assessment, carried out and signed off by a chartered professional, is required. |
| Basements and flood defences | New basements must be structurally independent from the flood defences, or sited outside of the zone of structural influence, whichever distance is greater. |
Climate Change Allowance:
L. Submitted FRAs should utilise the appropriate climate change scenarios when implementing the climate change allowances for surface water and fluvial flood risk. Assessments of tidal flood risk should use the current TE2100 crest levels guidance and breach modelling to account for worst-case scenarios.
For more information please see the Richmond Upon Thames Local Plan