Targeted Surface Water Control

Surface Water Drainage Strategy

Comprehensive Surface Water Drainage Strategy At Jgp

For all but the smallest new extensions or developments, a robust surface water drainage strategy is essential to manage the rate and location of surface water discharge. According to the National Planning Policy Framework (NPPF), the objective is to discharge surface water runoff as high up the following hierarchy of drainage options as reasonably practicable, in line with the CIRIA SUDS C753 Manual:

Expert Site & Ground Investigations

At JGP, our Geotechnical Engineers conduct comprehensive Site & Ground Investigations, including percolation and infiltration testing following BRE Digest 365. This informs the suitability of a site for infiltration. When infiltration is not feasible, onsite attenuation is a typical feature of surface water management systems, with various forms available. Our Drainage Engineers assess the local options to determine the most appropriate discharge scenario and advise on designing for exceedance.

Early Involvement for Multi-Dwelling Sites

For multi-dwelling sites, involving our drainage engineers early in the planning process is crucial to successfully incorporate above-ground SuDs features into the site’s surface water management strategy. This demonstrates to the Lead Local Flood Authority (LLFA) or the Local Drainage Team that SuDs are being used to manage the site’s surface water, meeting the four pillars of SuDs design: water quantity, water quality, public amenity, and biodiversity.

Collaborative Approach

We collaborate with you or your architect (landscape) to achieve the best fit for your site and budget while striving to meet local authority standards. Coordination with the project geotechnical team is advised to determine the optimal location for SuDs features and infiltration testing. Testing results help us decide whether infiltration is a viable means of surface water discharge. We use hydraulic modelling to determine the site’s greenfield runoff and developed state runoff characteristics, which helps in sizing the required infiltration device or attenuation and determining the allowable rate of discharge.

Benefits of Sustainable Urban Drainage Systems (SuDs)

SuDs are designed to control surface water runoff close to where it falls, mimicking natural drainage and providing amenity and biodiversity benefits. They are often more cost-effective than traditional “harder civil solutions” when space allows. SuDs offer opportunities to:

Planning & Approval

At the planning stage, unless the site is less than 1ha in flood zone 1, a Surface Water Drainage Strategy will accompany a Flood Risk Assessment. For large sites or complex systems, developing the surface water strategy into a detailed Surface Water Design for approval by the Lead Local Flood Authority is necessary, providing the contractor with essential construction details. If the site is in a critical drainage area (CDA), JGP can assist with that as well.

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