Flood risk within the development

Flood risk within the development

The drainage system must be designed so that, unless an area is designated to hold and /or convey water as part of the design, flooding does not occur during a 1 in 100 year rainfall event + 40% for climate change in any part of a building (including a basement); or in any utility plant susceptible to water (for example, pumping station or electricity substation) within the development.

Any attenuation feature should be designed to attenuate all flows up to and including the 1 in 100 year event + 40% for climate change.

The design of the site must ensure that, so far as is reasonably practicable, flows resulting from rainfall in excess of a 1 in 100 year rainfall event + 40% for climate change are managed in exceedance routes that minimise the risks to people and property.

With regards to ground conditions and the opportunity for infiltration, your FRA should include an assessment of the current and post development ground characteristics. Furthermore, for brownfield sites a topographic survey identifying the positively drained areas should be included. A betterment of 40% is expected as a minimum for brownfield site developments.

GCC as the LLFA may not be consulted or make bespoke flood risk comment on all applications or preapplication enquiries but this does not remove the need to submit FRAs for consideration by the council.

You may need to contact your Local Planning Authority or GCC as the Lead Local Flood Authority to discuss proposals in or adjacent to ordinary watercourses and local flooding issues related to them.

We may also advise on detailed surface water management proposals.

We do not recommend individual FRA consultants but the Chartered Institution of Water and Environmental Management (CIWEM) may help you to source a suitably qualified person.