London Borough of Sutton Local Flood Risk Policies

The London Borough of Sutton adopted their local plan in 2018 and it covers the period from 2016 to 2031. There are some 40 policies covering different planning requirements – policy 32 cover flood risk and drainage.

In addition, Sutton also has Guidance Note 3, published in 2013 and the Local Flood Risk Management Strategy (2015) which details the critical drainage areas within Sutton. Policy 32 states that:

Flood Risk Management

Proposed developments should avoid or minimise all sources of flood risk to people and property, taking account of climate change, without increasing flood risk elsewhere by:

• Preparing site-specific flood risk assessments (FRAs) in support of all proposals in Flood Zones 2 or 3, all major proposals in Flood Zone 1 over 1ha and any proposal in a critical drainage area. FRAs should assess all sources of flood risk to and from the development and show how these risks will be managed, taking climate change into account, in line with minimum requirements set out in national planning policy.

• Avoiding inappropriate development in flood risk areas in line with the ‘sequential’ and ‘exceptions tests’, taking account of government vulnerability classifications and flood zone compatibility guidelines. Allocated sites in flood risk areas should be developed having regard to the recommendations in the SFRA Level 2 Report as amended.

• Applying a ‘sequential approach’ to site layout by locating the most vulnerable development within areas of lowest flood risk where possible. All buildings should be set back at least 8m from the banks of main rivers and 5m from the banks of ordinary watercourses to allow improvements and maintenance of land drainage, improve the ecological functioning of river corridors and enhance local amenity.

• Ensuring that all ‘more vulnerable’ and ‘highly vulnerable’ developments within Flood Zones 2 and 3 set finished floor levels a minimum of 300mm above the modelled 1 in 100 annual probability flood level including climate change in accordance with the latest guidance published by the Environment Agency.

• Ensuring that any residual risks are safely mitigated through the use of flood resistance or resilience measures, including safe access and escape routes where required.

Sustainable Drainage (SuDS)

Proposed developments should incorporate effective sustainable drainage (SuDS) measures as part of the design and layout of the development in order to manage surface water run-off as close to its source as possible and achieve the following minimum SuDS performance standards through application of the Mayor’s drainage hierarchy:

• Greenfield sites: ensure that peak run-off rates and volumes for the 1 in 100 year rainfall event never exceed greenfield run-off rates for the same event.

• Previously developed sites: ensure that peak run-off rates and volumes for the 1 in 100 year event achieve greenfield run-off rates for the same event, unless it can be demonstrated that all opportunities to minimise final site run-off, as close as reasonably practicable to greenfield runoff rates, have been taken in line with the Mayor’s drainage hierarchy. In such cases, run-off rates must not exceed 3 times the calculated greenfield rate in accordance with the Mayor’s Sustainable Design and Construction SPG; and

• ensure that the site drainage strategy can contain the 1 in 30 year event (+ climate change) without flooding and that any flooding occurring between the 1 in 30 and 1 in 100 year event (+ climate change) will be safely contained on site.

All major development proposals should be accompanied by a Drainage Assessment Form and relevant surface water run-off calculations to demonstrate that the council’s minimum SuDS performance standards in Part (b) have been met, having regard to national SuDS standards, London Plan Policy 5.13, the Mayor’s Sustainable Design and Construction Supplementary Planning Guidance (SPG), Sutton’s SFRA Level 1 Report and other sources of guidance and best practice.

All development proposals should include details of how each SuDS measure, and the site drainage strategy as a whole, will be managed and maintained throughout its lifetime, including proposed arrangements for adoption where relevant.

All proposed SuDS measures should be designed to contribute towards the aims of Policy 33 ‘Climate Change Adaptation’, Policy 34 ‘Environmental Protection’, Policy 26 ‘Biodiversity’ with regard to urban cooling, biodiversity, water resources, air quality and creating linked networks of blue and green spaces. Developments adjacent to the Wandle should seek to contribute to the aims of: Policy 5 ‘Wandle Valley Renewal’, the Wandle Catchment Plan, the Mayor’s All London ‘Green Grid’ EA’s Thames Basin Management Plan.

How does Policy 32 impact on Proposed Development?

Sutton’s Policy 32 measnt that, if you are required to produce a flood risk assessment for a development, you will also likely be asked to produce a SuDS strategy (or a SuDS statement for smaller developments).

Flood Risk Assessments by Aegaea

Aegaea has successfully delivered flood risk assessments across the Borough of Sutton for a variety of clients, so get in touch with one of our consultants and see how Aegaea can offer you professional, expert advice.

(and if you’re really in need of help, one of our team lives there, so they can come out and see you!)