Application of the hierarchy for managing surface water will be a key requirement of all new development to reduce flood risk and the impact on the environment. Clear evidence must be submitted to demonstrate why alternative preferable site options in the surface water hierarchy are not available. Foul and surface water drainage must be considered early in the design process. Sustainable drainage must be integrated with the landscaped environment and designed in accordance with the four pillars of sustainable drainage (water quantity, water quality, amenity and biodiversity). It should identify SuDS opportunities, including retrofit SuDS opportunities, such as green roofs, permeable surfacing; soakaways, filter drainage, swales, bioretention tree pits, rain gardens, basins, ponds reedbeds and wetlands. Any drainage should be designed in accordance with ‘Ciria C753 The SuDS Manual’, sewerage sector guidance, or any subsequent replacement guidance.

There could be potential for surface water drainage to the canals, subject to separate agreement of the Canal and River Trust (on a case-by-case basis).

The hydrological assessment of the site must consider site topography, naturally occurring flow paths, ephemeral watercourses and any low-lying areas where water naturally accumulates. Applicants need to consider exceedance/overland flow paths from existing and proposed drainage features and confirm ground levels, finished floor levels and drainage details, which are critical to ensure proposals are resilient to flood risk and climate change. Holistic site-wide drainage strategies for foul and surface water should ensure a co-ordinated approach to drainage between phases. Applicants should demonstrate interconnecting phases within larger sites and updated between each phase. Liaison with infrastructure providers is necessary.

In relation to new development, it is up to the Local Planning Authority (LPA) to determine whether the flood warning and evacuation plans, or equivalent procedures, are sufficient or not. Developments that include areas that are designed to flood (e.g. ground floor car parking and amenity areas) or have a residual risk associated with them, will need to provide appropriate flood warning and instructions so users and residents are safe in a flood. This will include both physical warning signs and written flood warning and evacuation plans. Those using the new development should be made aware of any evacuation plans.

A drainage assessment at the outset can determine:

If the site can be adequately developed

Land-take required for the proposed drainage

The impact of the development on the downstream catchment

Scope for future development

Sensitivity of the area

Appropriate drainage to give the best possible environmental protection