Validation Checklist - List 1

3zv Sustainable Urban Drainage Systems and Foul Sewage Assessment

Required for:
A surface water drainage assessment should be carried out and submitted to demonstrate that the proposed development will not create an increased risk of flooding from surface water to the development site and the surrounding area. Sustainable urban drainage systems (SuDS) is required to support major applications where developments of ten dwellings or more and equivalent non- residential schemes. Applications will need to be supported by the following information.

Applications will not be made valid without this information:
1. Detailed site layout at an identified scale
2. Topographical survey of the site
3. Plans, drawings and specification of SuDS proposed. This should include detail of hard construction, soft landscaping and planting
4. Calculations of discharge and run-off rates, water storage capacity of the proposals, and demonstration that they meet the requirements of the site
5. Evidence that the discharge hierarchy has been assessed and at least one discharge mechanism is confirmed (infiltration test results, adequacy of the receiving waterbody or in last resort agreement to connect to the sewer network)
6. Details of any offsite works required, together with necessary consents
7. Management and maintenance plan for all SuDS

Plans and details shall be submitted to ensure that sustainable drainage systems for the management of run-off are put in place, unless demonstrated to be inappropriate.

Applications for development should also demonstrate that there is adequate capacity both on and off the site to serve the development and that it would not lead to adverse amenity impacts for existing or future users in the form of internal and external sewer flooding or pollution of land and water courses.

Any works proposed to be carried out that may affect the flow within an ordinary watercourse will require the prior written consent from the Lead Local Flood Authority under Section 23 of the Land Drainage Act 1991. This includes any permanent and or temporary works regardless of any planning permission.

Appraisals and reports may be required to ascertain whether the proposed development will lead to overloading of existing water and/or waste water infrastructure. Where there is a capacity constraint, as identified by Thames Water, the developer shall provide a detailed water and/or drainage strategy informing what infrastructure is required, where, when and how it will be delivered.

When the proposed development results in any changes/replacement to the existing system or the creation of a new system, scale plans of the new foul drainage arrangements will also need to be provided. This will include a location plan, cross sections/elevations and specification. If connection to any of the above requires crossing land that is not in the applicant’s ownership, other than on a public highway, then notice may need to be served on the owners of that land.

Policy Driver and where to get more advice: Policies R7 and R9 of the Welwyn Hatfield District Plan 2005 Policies SADM14, SP10 and SADM13 of the Draft Local Plan Proposed Submission, August 2016. National Planning Policy Framework. Sections 10 and 11. Surface water drainage. Flooding and water - HCC.