In our last post, “What is a drainage assessment”, we considered the main factors that could affect drainage on a proposed site that would need initial risk assessment to inform a more detailed approach to the development’s drainage strategy.
Now, we turn to the main components of a drainage strategy required for major developments (10 dwellings or above) that are required by Local Planning Authorities (LPAs).
Approaches vary by LPA, but a typical drainage strategy usually defines:
In an application, developers will need to show that the excess runoff will be managed effectively and not cause an increase in flood risk anywhere else, i.e. both to and from the site.
SuDS are now a material planning consideration for major developments of 10 dwellings or more and equivalent non-residential schemes.
Councils will usually wish to reduce the need for pre-commencement conditions, but drainage is always viewed as critical to be agreed prior to work beginning on site.
Therefore to speed up the review of proposals, drainage consultants need to design the drainage strategy to an appropriate standard of detail.
These as minimum contain and demonstrate the following points:
2. Plans, drawings and specification of SuDS proposed, integrated with landscaping and materials requirements.
It is expected that design, drainage and landscaping consultants coordinate and integrate plans to create the final design.
3. Demonstration of the consideration of the spectrum of SuDS in accordance with the SuDS hierarchy, ideally using a variety of options and clear justification provided where the most sustainable solution cannot be provided.
4. Section 106 may be considered for off-site works where these standards cannot be met.
5. Information on the receptors of the drainage system.
6. Methods of appropriate water quality control provided.
7. A condition will be added to planning decisions, or developers will be expected to enter into a legal agreement under S106 of the Town and Country Planning Act 1990 (as amended). An example of an appropriate management plan can be found on Susdrain – Useful frameworks and checklists.
An essential first step to the right design is to understand the ground drainage conditions and the site’s suitability for infiltration. GeoSmart’s range of Drainage Assessment Reports, SuDSmart, provides an overview of site suitability for a range of SuDS options.
They can also provide run-off calculations and initial SuDS designs, which can be used as part of the drainage strategy submission to the LPA.
For more information, contact us on 01743 298100 or email firstname.lastname@example.org
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