Based on the Environment Agency’s Flood Risk from Surface Water mapping, part of the site is shown to have a high risk of surface water flooding. Our strategy would be as follows:
Where possible, retail units will be raised above the estimated level of historic flooding
Raised vehicle crossovers at entrances will be designed to reduce the likelihood of lower order rainfall events affecting the site
Automatic flood defences at building entrances to the service yard to prevent flooding of the building in the higher order rainfall events.
Historic records indicate that the wider Caterham area is susceptible to flooding due to groundwater. However, after desk based research, a review of records of past onsite flood events and consultation with both the Environment Agency and the Council, it is understood that groundwater flooding affecting the site itself is unlikely. Additionally both Surrey County Council and Tandridge have advised that they hold no records of any hidden or lost watercourses running beneath or in close proximity to the site.
Surface water runoff would be managed through below ground attenuation within the new service yard and a number of soakaways located external to the building. The surface water drainage system would be designed in line with current best practice guidance for the 1 in 100 year rainfall event incorporating an allowance of 40% for climate change.