A flood risk assessment is a pre-development service often combined with a contaminated land investigation, geotechnical investigation and or sustainable drainage plan. By combining the services there is a potential to save considerable development costs and time.
A preliminary assessment is highly recommended for all sites to determine whether they are located within or close to Flood Zone 1. The size of the planned development has an impact on the detail of any potential flood risk assessment, sites in excess of 1 hectare in size require a Flood Risk Assessment regardless of proximity to a Flood Zone. It is best practice for all sites to assessed against the risks from flooding.
A flood risk assessment would be undertaken looking at the risk from each potential flooding mechanism to the site:
This would be confirmed by reference to any site specific flood risk assessments previously commissioned by the Local Authority and reference to the Strategic Flood Risk Assessment for the area including any potential pluvial (ponding) surface water flooding. The context of the site in terms of local hydrology, hydrogeology and flood risk will be established and used to inform the surface water drainage assessment. A review of the flood risk posed by the site to offsite receptors would be included under the item dealing with run-off attenuation measures within the drainage design element of the works.
Based on the findings of the FRA any necessary potential flood mitigation measures would be proposed with the associated cost implications necessary to reduce the risk and allow the development to proceed.
We have undertaken work for both Developers and Local Authorities including extensive flood risk assessments and drainage plans during the rehabilitation of brownfield sites. Work is undertaken on a range of scales to meet address the risks posed to individual sites.
Bob Sargent is our technical lead on urban development, he has experience of supporting the development of complex sites that have in some cases required Expert Witness level support to gain planning approval.