Strategic Flood Risk Assessment - South Worcestershire ...

Soil TypeGreenfield Runoff Rate (l/s/ha)Fluvial DepositsEstimated Attenuation Storage Volume (m 3 ) 378 – 514SUDS and the development site:SUDS TypePotentialSuitabilityComments1 in 2 year 7.41 in 100 year (plus climate change) 27.6Source ControlInfiltrationDetentionFiltrationConveyanceAll forms of source control are likely to be suitableMapping suggests underlying soil is likely to be permeable.However; the high risk of groundwater flooding would makeinfiltration unsuitableMapping suggests that site slopes are steep and detention storage‘above ground’ may therefore may not be viableAll forms of filtration are likely to be suitableMapping suggests that site slopes would be suitable for conveyance.However, due to the steepness of slope may require check dams toslow flowsFlood Defences:None.This site is located within a flooding hotspot so all efforts should be made tominimise the rate and volume of runoff leaving the site.The site is not located within a groundwater source protection zone.Mixed use developments should provide at least two independent SUDS features inseries to provide a suitable level of water quality treatment.Effects of Climate Change:Increased rainfall intensities. Increased water levels in the River Salwarpe.Flood Risk Implications for Development:All development should be located within Flood Zone 1, unless appropriate inaccordance with NPPF Technical Guidance.A detailed site-specific flood risk assessment, including hazard mapping, will berequired for any development in Flood Zone 2, or for sites greater than 1ha in FloodZone 1.Redevelopment or alternative use of the site will focus on mixed use proposals.Resilience measures will be required if buildings are situated in the flood risk area.Green infrastructure should be considered within the mitigation measures forsurface water runoff from potential developmentAssessment for runoff should include allowance for climate change effectsNew or re-development should adopt exemplar source control SUDS techniques toreduce the risk of frequent low impact flooding due to post-development runoff.The site falls within an area indicated to potentially be susceptible to groundwateremergence. Further assessment of groundwater risk would be required and anassessment of suitable surface water mitigation techniques should be made at thedetailed FRA level.Onsite attenuation schemes would need to be tested against the hydrograph of thereceiving watercourse to ensure flows are not exacerbated downstream within thecatchment.The Hampton road and the B4090 Saltway road, the main access roads to the siteare at risk from fluvial flooding and \ or surface water. Suitable alternative accessarrangements away from the floodplain will need to be investigated further.Demonstration that development at this location can be made safe.2012s5947 S Worcestershire Level 2 SFRA Update FINAL Report v1.0.doc 110