| Conditions or Reasons: | 13)
Prior to the commencement of development a final detailed design of the surface water drainage scheme, to manage surface water runoff from the development for up to and including the 1 in 100 year event (+40%CC), shall be submitted to and approved in writing by the Local Planning Authority. The discharge rate from the development will be limited to the equivalent 1 in 1 year rate, or an appropriate rate as agreed by the Local Planning Authority. The final detailed design shall be based on the agreed 'Flood Risk Assessment / Sustainable Urban Drainage Systems (SuDS)' (Ref: QFRA 1561, v1.1, 05/2020). The approved drainage works shall be completed prior to the completion or occupation of the development on site whichever is the sooner, and shall be subsequently maintained as approved.
Full calculations detailing the existing surface water runoff rates for the QBAR, 3.3% Annual Exceedance Probability (AEP) (1 in 30) and 1% APE (1 in 100) storm events;
Full results of the proposed drainage system modelling in the above-referenced storm events (as well as 1% APE plus climate change) , inclusive of all collection, conveyance, storage, flow control and disposal elements and including an allowance for urban creep, together with an assessment of system performance;
Details of the arrangements to manage the parts of the site at current risk of surface water flooding, through the design of the surface water drainage system to be provided.
Detailed drawings of the entire proposed surface water drainage system, including levels, gradients, dimensions and pipe reference numbers, attenuation, flow and pollution control measures.
Integration of the drainage system with wider site objectives, including water quality treatment, amenity, biodiversity and Amenity.
Site Investigation and test results to determine potential for infiltration and design constraints of the drainage system;
Agreement from Anglian Water to connect to the offside public surface water sewer network.
Details of overland flood flow routes in the event of system exceeding, with demonstration that such flows can be appropriately managed on site without increasing flood risk to occupants;
Details of the structural integrity, proposed construction of the system, and any phasing of works.
Full details of the maintenance/adoption of the surface water drainage system, in its entirety, and any proposed split of the surface water management system and/or maintenance responsibilities between private (i.e. within cartilage) and public (i.e. in public open space and/or highway).
Reason: To ensure the approved system will function to a satisfactory minimum standard of operation and prevent the increased risk of flooding both on and off site for the lifetime of the development in accordance with Section 14 of the NPPF February 2019, its supporting technical guidance and the Technical Standards for Sustainable Drainage Systems (DEFRA, 2015) and CIRCA SUDS Manual, and to ensure that the implementation and long term operation of a sustainable drainage system. |
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