Strategic Flood Risk Assessment - South Worcestershire ...

etween the proposed level of commitment and the future needs to support growth thenit will be a priority for the Flood Risk Management Strategy to be reviewedThe standard of safety must be maintained for the intended lifetime of the development(assumed to be 100 years for residential development). Over time the effects of climatechange will erode the present day standard of protection afforded by defences and socommitment is needed to invest in the maintenance and upgrade of defences if thepresent day levels of protection are to be maintainedThe assessment of actual risk can include consideration of the magnitude of the hazardposed by flooding. By understanding the depth, velocity, speed of onset and rate of riseof floodwater it is possible to assess the level of hazard posed by flood events from therespective sources. This assessment will be needed in circumstances whereconsideration is given to the mitigation of the consequences of flooding or where it isproposed to place lower vulnerability development in areas that are at risk frominundationThose using the South Worcestershire Level 2 SFRA Update should refer to the EnvironmentAgency's National Flood and Coastal Defence Dataset (NFCDD) for details on the standard ofprotection of defences.4.2.4 Residual RiskThe residual risk refers to the risks that remain in circumstances where measures have beentaken to alleviate flooding. It is important that these risks are quantified to confirm that theconsequences can be safely managed. The residual risk can be:The effects of a flood with a magnitude greater than that for which the defences ormanagement measures have been designed to alleviate. This can result in over toppingof flood banks, failure of flood gates to cope with the level of flow or failure of pumpingsystems to cope with the incoming discharges; orFailure of the defences or flood risk management measures to perform their intendedduty. This could be breach failure of flood embankments, failure of flood gates tooperate in the intended manner or failure of pumping stations.The assessment of residual risk demands that attention be given to the vulnerability of thereceptors and the response to managing the resultant flood emergency. In this instanceattention should be paid to the characteristics of flood emergencies and the roles andresponsibilities during such events.4.3 Possible responses to flooding4.3.1 Assess4.3.2 AvoidThe first response to flooding must be to understand the nature and frequency of the risk. Theassessment of risk is not just performed as a "one off" during the process, but rather theassessment of risk should be performed during all subsequent stages of responding to flooding.The sequential approach requires that the first requirement is to avoid the hazard. If it ispossible to place all new growth in areas at a low probability of flooding then the flood riskmanagement considerations will relate solely to ensuring that proposed development does notincrease the probability of flooding to others. This can be achieved by implementing SUDSsystems and other measures to control and manage run-off. In some circumstances it might bepossible to include measures within proposed growth areas that reduce the probability offlooding to others and assist existing communities to adapt to the effects of climate change. Insuch circumstances the growth proposals should include features that can deliver the necessarylevels of mitigation so that the standards of protection and probability of flooding are not reducedby the effects of climate change. In South Worcestershire, consideration should be given notonly to the peak flows generated by new development but also to the volumes generated duringlonger duration storm events2012s5947 S Worcestershire Level 2 SFRA Update FINAL Report v1.0.doc 26