Sustainable Drainage Systems Major Design Guidance

The Applicant must follow the hierarchy set out in Standard 1.1 of the National standards for sustainable drainage systems.

RBWM is located within a ‘Water Stressed Area’ as defined in the Environment Agency’s Water stress areas – 2021 classification Policy Paper and therefore Priority 1 will always be required as per 1.11 of the National standards for sustainable drainage systems.

It is acknowledged that Priority 1 (collected for non-potable use) will normally be proposed in conjunction with another lower order priority, in many cases an outfall from the site will be required (e.g. to ground or off-site).

There are areas of the borough that are only served by foul sewers, in these circumstances where a higher priority outfall has been demonstrated as unfeasible (with supporting evidence submitted), there may be a requirement for a connection to the foul sewer subject to the approval of the sewerage authority.

Evidence must be provided at the planning application stage. If infiltration test results are not available to support a planning application, then justification as to why these have not been provided should be included. For example, issues with site access i.e. the site is a working brownfield site and as such it is not possible to dig trial pits. Justifications should be submitted alongside a suitable desk study of ground conditions and they will be reviewed on a case-by-case basis.

In the borough there are areas where deep bore soakaways may be an appropriate method of draining the site with appropriate water quality and geotechnical considerations, subject to any necessary approvals from the Environment Agency.

RBWM LLFA will not be considering use of 1.6.1 from the National standards for sustainable drainage systems.

For discharge to a watercourse the applicant must demonstrate the onward connectivity, condition and capacity of the watercourse to receive flows.

New private surface water drainage will not be allowed to discharge into a highway drainage system.

If the development site has an existing connection to the highway drainage system, please contact flooding.enquiries@rbwm.gov.uk to discuss the proposals.

Surface water from private land must not discharge onto the public highway surface or into the public highway drainage system.

The granting of planning permission and agreement of the principles of how surface water will be disposed of from a site does not absolve the requirement to gain Ordinary Watercourse Consent or an Environmental Permit when connecting to a watercourse. The Applicant must refer to the need to obtain any consents, licences or permissions within their drainage strategy, and their current status.