Sustainable Drainage Systems Design Guidance

In areas where ground conditions are not suitable to infiltrate, surface water can be discharged to suitable nearby waterbodies. The discharge location should aim to mirror the greenfield hydrological situation. The ability of existing watercourses to convey water (and to function as an effective exceedance flow route, where appropriate) will always need to be maintained.

Evidence should be provided to show the suitability of the waterbody to receive flows. This could include a topographical survey showing banks and bed levels which confirm a gravity connection is achievable.

Proposed use of existing ponds or lakes must be accompanied by calculations showing that the waterbody has appropriate capacity to receive the incoming flows without increasing flood risk and that a suitable outfall or infiltration rate is present or proposed.

Details confirming water can freely flow within a receiving watercourse without obstruction or confirmation that the channel will be cleared prior to development should be provided.

The applicant should confirm that they understand that any connection or alterations made to an Watercourse may require consent or permit:

Ordinary Watercourse Consent is required under Section 23 of the Land Drainage Act 1991 where alterations are proposed to an Ordinary Watercourse.

Works on or near a Main River may require a Flood Risk Activity Permit (FRAP) from the Environment Agency. For more information on FRAPs, please contact the Environment Agency.

Where appropriate third party permissions should be sought and evidenced for connections crossing land outside the red line boundary of the application. If watercourses are within or adjacent to the redline boundary of the site, future riparian access and maintenance should be considered within the design and detailed in the maintenance and management plan.