The existing predevelopment site falls generally from north west to south east with surface water runoff towards Harpers Brook, which is situated in the far south eastern corner of the site.

The site is in Flood Zone 1 and is therefore at low risk of flooding from tidal and river sources. It is proposed that the drainage strategy for the proposed development mimics the existing scenario with all the plots discharging unrestricted to a sitewide drainage system which will convey surface water to the south of the site to the site wide attenuation which will be created in the former railway cuttings.

As part of the strategy, these cuttings have been enhanced and modified to act as sustainable drainage attenuation features which will provide a benefit in a number of ways. Notably, improving the ecological environment, water quality and importantly slowing the runoff to ensure it discharges at greenfield rate (2 l/s/Ha) to Harpers Brook.

Each plot will benefit from a self-contained drainage system which will be designed to ensure that the runoff is treated on plot with the use of petrol interceptors for yards and car parks and additional SuDS techniques where applicable prior to discharge to the sitewide system.

The greenfield runoff rate of has been agreed with the LLFA previously and represents a significant improvement in the most extreme storm events with climate change allowance applied.

This will ensure that the flood risk is managed downstream through the additional attenuation on site.