Flood Risk Assessment

The scope and details of the Flood Risk Assessments will vary depending on the size and topography of the site, and which Flood Zone the site lies within.

The flood zone for a sites are obtained from the Environment Agency and Local Authority Strategic Flood Risk Assessment which are defined as Flood Zone 1 to Flood Zone 3, and the site areas being defined as more or less than 1 hectare.

(Flood Zone 1 is has 1 in 1000 (0.1%) or less annual probability of flooding, Flood Zone 2 has between 1 in 1000 (0.1%) to 1 in 100 (1%) annual probability of flooding, and Flood Zone 3 has more than a 1 in 100 (1%) annual probability of flooding).

The minimum Flood Risk Assessment we provide that is required for most planning approvals is for sites that are less than 1 hectare in size and lie within Flood Zone 1.

In this circumstance, The Environment Agency Advice Note – April 2012 states that no flood risk assessment will be required, but a Flood Risk Statement and Surface Water Management of the site is required to demonstrate that the proposed development will not increase the risk of flooding to the site or surrounding areas.

• Details of each potential source of flood risks to the development site;
• Pre and post development surface water run-off rates and volumes for up to and including a 1 in 100 year storm event including climate change (analysis using industry recognised calculations obtained from XP Solutions WinDes computer software);
• Mitigation factors to be incorporated into the design of the development to minimise the risk of flooding

In some circumstances the development site may lie within Flood Zone 3 and is over 1 hectare in size. This will be the most detailed flood risk assessment required to obtain planning permission for a development, and the steps below are to be taken as minimum.

The National Planning Policy Framework guidelines and details are also to be adhered to in this circumstance. The full flood risk assessment for this will include:-

• Site sequential and exception test assessment for the development;
• Sources of flood risk within the vicinity of the development site;
• Flood risk mitigations design techniques;
• Flood compensation levels and volumes requirement within the development site boundary to maintain the functional flood plain;
• Pre and post development surface water run-off rates and volumes for up to and including a 1 in 100 year storm event including climate change (analysis using industry recognised calculations obtained from XP Solutions WinDes computer software);
• Safe egress assessment for evacuation off the post development site.