RPA is experienced in undertaking flood risk assessments to accompany planning applications following Planning Policy Statement 25 (PPS25) and Environment Agency guidance notes. Our approach covers identification of the sources of flooding, existing defences and the impacts of flooding on the proposed development site as the basis for estimating the current flood risk at the site. Where appropriate, we make use of the Environment Agency’s breach analysis model (which we are also able to use for overtopping analysis). Future changes to flood risk, based on Defra guidance, and residual risks are also identified, as are recommendations for resilience.
The approach taken depends on the particular needs of the client and FRAs have been produced for barn conversions to large residential developments.
Flood Risk Methodologies
RPA has been involved with the development of methodologies for the assessment of flood risk for many years. RPA contributed to Defra's guidance on risk assessment in flood and coastal defence, FCDPAG4 Approaches to Risk, published in 2000.
RPA has been involved in a major study for Defra to provide a methodology that can be used to estimate the number of injuries or deaths for a given flood event. The Flood Risks to People methodology is designed to be used at three different levels:
- local scale: for emergency response by identifying areas of greatest risk and most vulnerable people;
- catchment to regional scale: for flood risk and vulnerability mapping for use in catchment scale flood mapping, land use planning and targeting of flood warning; and
- national scale: for scenario testing and policy appraisal.
The methodology is based on depth and velocity of flood waters, as the two most important variables for mapping flood hazard and develops an equation that can be used to calculate the number of deaths and injuries:
N (I) = N x X x Y
Where: N(I) is the number of deaths or injuries
N is the population within the floodplain
X is the proportion of the population exposed to a risk of suffering death or injury
Y is the proportion of those at risk who will suffer death or injury
The approach also includes methods for calculating X and Y, based on the degree of hazard by location within the floodplain and whether there has been a flood warning (or not), the speed of onset of flooding, the nature of the area and the timing of the flood.
