FRA leaf and textRammSanderson Ecology Ltd are experienced in preparing site specific Flood Risk Assessment (FRA) to National Planning Policy Framework (NPPF) and TAN15 standards suitable for planning. It is usual for the Environment Agency (EA) to raise an objection to a planning application for sites in excess of one hectare or those located within Flood Zones 2 or 3 of the EA flood maps until the question of flood risk has been appropriately assessed.

Our FRA’s are individually prepared based on the sites proximity to watercourses, the size of the site, the sites topography and pre and post development land use. We undertake a thorough walk-over survey of each individual site to assess any structure or watercourse likely to affect local hydraulics in accordance with EA guidance notes.  Our reports include a comprehensive review of information provided through consultation with the Environment Agency, Internal Drainage Boards (IDB), local authority and utilities companies.

Specific consideration is given to the local Strategic Flood Risk Assessment (SFRA) which often highlights areas susceptible to flooding as well as areas allocated for future development. An assessment of information included on sequentially preferable sites is made to consider whether the sites function/use is appropriate within these allocated development areas.

Our flood risk specialists are experienced in completing surface water runoff assessments for both Greenfield and Brownfield sites. This considers the effects a change in permeability can have on the site and local hydraulics. To manage the risk of flooding associated with surface water runoff our detailed reports include a review of pre and post development surface water runoff conditions using the Wallingford Procedure (modified rationale method) and the Institute of Hydrology Report 124 Method. Calculations include an allowance for climate change and look to better the existing runoff conditions of the site in line with best practice guidelines.

Whilst our reports include recommendations to mitigate against the effect of fluvial flooding (such as resistant & resilient design & raising of floor levels, amongst other things) we also include site specific recommendations for access and egress (which must be provided above the 1 in 100 year flood level), flood warning and evacuation procedures and sustainable drainage.

Our approach to drainage follows document H3 of the Building Regulations 2000 (as amended), which detail a hierarchy for surface water disposal. Where possible infiltration drainage is recommended, primarily through natural processes or the implementation of permeable paving. Where this is not possible gullies and drains are recommended to direct runoff to watercourses or permeable land within the site. The discharge of surface water to a sewer network is only recommended as a last resort to prevent deterioration in performance.

All our FRA’s include an indicative drainage proposal, tailored to the site to incorporate Sustainable Drainage Systems (SuDS). SuDS help to reproduce the natural drainage conditions of a site and should be implemented where possible.

According to the Environment Agency National Assessment of Flood Risk (2009), 2.4million properties are at risk of flooding from rivers and the sea in England whilst 3.8million properties are susceptible to surface water flooding. Only approximately 55% of the people living in flood risk areas know they are at risk. Combined the damage caused by all flood mechanisms cost over £1billion each year. To see if your property or site is at risk of flooding click here.

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