flood risk assessment in connection with a planning - Breckland ...

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Flood Risk Assessment Tesco Supermarket, Swaffham 7.0 OFFSITE AND RESIDUAL IMPACTS 7.1 Remaining on-site Risks The site is currently defended from possible flooding by existing site levels. All surface water drainage systems will be designed to incorporate climate change over the proposed lifetime of the development. No significant on site risks remain. 7.2 Management of Residual Risks There are no residual risks requiring specific management measures. The management of the proposed surface water systems (those which are unadoptable by the statutory drainage provider) will be by the responsibly site owners or agreed designated management company. Page 17 Jubb Consulting Engineers Limited February 2012 P9632-G300C-Rep-120209-MH
Flood Risk Assessment Tesco Supermarket, Swaffham 8.0 FLOOD RISK ASSESSMENT SUMMARY 8.1 Existing Conditions The site is currently a brownfield area of land. 8.2 Requirements A site specific FRA has been carried out for the site by Jubb Consulting Engineers Ltd as reported herein. In summary this Flood Risk Assessment assesses the following – sources of flooding; existing surface water disposal; proposed surface water management (Including SUDS); adequacy of the existing defences; the effect of climate change; means of emergency escape and access; offsite flood risk and the effect of increased impermeable surface area on the downstream environment; residual risk. 8.3 Assessment For the foregoing, the risk against each of these considerations has been assessed as follows – the primary source of potential flooding identified at the subject site is from extreme onsite surface water flows; current flood defences to the site are provided by existing ground levels; surface water discharges from the existing site currently soak into the ground via natural infiltration; the proposed development is to be defended against a minimum of a 100 year return period event extreme surface water flood event, plus an allowance for climate change over a design life (60 years for residential); the use of appropriate detention storage with capacity to infiltrate discharges to ground during extreme events will ensure that the proposed development will not increase the risk of flooding to any off-site properties; where possible drainage by means of sustainable drainage systems (SUDS) will be employed, with the promotion of infiltration as the primary option for surface water disposal. 8.4 Flood Risk to the Development The development site is located within a Flood Zone 1 (Low annual probability of fluvial and tidal flooding; i.e. land assessed as having less Page 18 Jubb Consulting Engineers Limited February 2012 P9632-G300C-Rep-120209-MH
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