Flood Risk Assessment (FRA)

A Flood Risk Assessment (FRA) is required for any development that is proposed within Flood Zones 2 or 3 (within the 1 in 100 year or 1 in 1000 year floodplain); for any development with an area greater than 1ha; or where the development lies within close proximity of a watercourse or within an area with a history of flooding. The need for a Flood Risk Assessment is generally determined by the Environment Agency (EA), Environment Agency Wales (EAW) or the Scottish Environmental Protection Agency (SEPA) during consultation with the Local Planning Authority.

The Assessment determines the risk of flooding not only from rivers (fluvial flooding) or the sea (coastal flooding) but also from other sources such as groundwater, land drainage and sewer flooding. A key part of the assessment is the consideration of potential flooding from surface water runoff (pluvial flooding) including possible overland flows.

Clear has a significant amount of experience in undertaking FRAs all over the UK. In England, FRAs are undertaken in accordance with PPS25 while in Scotland they are undertaken in accordance with SPP7. FRAs are undertaken in line with PPS15 in Northern Ireland and Flood Consequence Assessments (FCA) are undertaken to TAN15 in Wales. Since 2004 we have undertaken over 300 flood risk assessments of varying size and complexity across the UK.

In terms of costs and timescales in producing a Flood Risk Assessment this is dependent on the complexity of the flood risk issues at the site. Annex E of PPS25 provides guidance on the required complexity of a Flood Risk Assessment which, in summary, should be appropriate to the scale and potential impact of the development.

In all cases some level of consultation will be required with the EA, EAW or SEPA and where further data is available this will need to be formally requested from the EA. Timescales for receipt of this data can be up to 4 weeks and is a key factor in determining delivery dates.

A topographical survey to Ordnance Datum will also be required at all sites requiring a FRA. If this is not available we are able to arrange for topographical surveys to be undertaken.

In some cases, where existing flood data is not available, hydraulic modelling of watercourses may also be required to demonstrate the potential flood levels in the vicinity of the site.

Clear has a very strong track record in undertaking hydraulic modelling and in applying appropriate methodologies and software to suit site specific requirements. Hydraulic models are usually constructed using HEC-RAS, InfoWorks RS and InfoWorks CS. Where appropriate, we have undertaken modelling studies using 2-D overland flow modelling to demonstrate flood routes and flood depths.

Clear provides the following capabilities to support the completion of flood risk assessments:

  • Desktop investigations to utilise existing and historic data
  • Site surveys and topographical surveys
  • Hydrological studies
  • Hydraulic modelling
  • Drainage Impact Assessments
  • Outline SuDS design

Since 2004 Clear has undertaken over 300 flood risk assessments of varying size and complexity. We also undertake a large number of Drainage Area Studies for UK Water Companies, which also include significant data collection, modelling, analysis and flooding assessment. These skills and knowledge are complimentary to FRAs and SFRAs and enhance our capability in this discipline.