Strategic Flood Risk Assessment - South Worcestershire ...

impermeable surfaces may result in an increase of surface water flood risk. TheSalwarpe road, the main access roads to the site is at risk from surface water.Surface Water Drainage:As an indication of requirements to manage surface water runoff at the development site anassessment of the soil types, greenfield runoff rate and attenuation storage volume is includedbelow. Storage volumes displayed are calculated with an assumption that 75% of the site willbe developed impermeable ground. A 25% increase in rainfall depths has been included torepresent predicted future climate change effects.PLEASE NOTE: This assessment has been carried out using broad-scale datasets and aims toprovide an indication of the likely opportunities and constraints for this development site. Adetailed drainage assessment based on site-specific conditions should be carried out by asuitably qualified professional and submitted with any planning application. The values belowshould not be used for design purposes.Soil TypeGreenfield Runoff Rate (l/s/ha)Fluvial DepositsEstimated Attenuation Storage Volume (m 3 ) 481 – 655SUDS and the development site:1 in 2 year 7.41 in 100 year (plus climate change) 27.6SUDS TypeSource ControlInfiltrationDetentionFiltrationConveyancePotentialSuitabilityCommentsAll 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.Residential developments should provide at least two independent water treatmentstages SUDS features in series 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 is proposed to focus on residentialuses. Flood risk indicates that the site would not be suitable for residential uses.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.2012s5947 S Worcestershire Level 2 SFRA Update FINAL Report v1.0.doc 100