Conducting a Site-Specific Flood Risk Assessment (FRA)

A Flood Risk Assessment (FRA) is a crucial step in planning applications for developments in flood-prone areas. This blog explains the FRA process and its importance.

What is an FRA?

An FRA evaluates flood risks to a site and identifies measures to mitigate these risks. It ensures that developments:

• Are safe for occupants.

• Do not exacerbate flooding elsewhere.

• Remain safe and resilient for the duration of their intended lifespan (e.g., 100 years for residential developments and 75 years for commercial developments).

  
  

Steps in Conducting an FRA

1. Identify Flood Risks: Determine sources of flooding using flood maps, historical data, and future climate projections. Key sources to assess include:

   • Fluvial (river) flooding

   • Coastal flooding

   • Surface water runoff

   • Groundwater emergence

   • Reservoir failure

2. Assess Impacts: Evaluate how the development may affect flood risk locally and downstream. For instance, an increase in impermeable surfaces can heighten surface water flooding. Raising ground levels or increasing the built footprint in a flood zone can displace floodwaters, potentially exacerbating risks in surrounding areas by reducing available floodplain storage.

   
   

   It is also essential to note that the Flood Maps for Planning mapping does not account for climate change impacts. Consequently, assessing a site's risk across a development's lifespan requires a broader approach.

   
   

   Planners and Flood Risk Consultants must not solely rely on the Flood Maps for Planning but also review complementary data sources such as Strategic Flood Risk Assessments (SFRAs) and request specific climate change data projections from the Environment Agency. These additional data points ensure that assessments consider future flood zone extents and propose mitigation measures tailored to address both current and future risks effectively.

3. Mitigation Measures: Propose solutions to minimize risk and impact. Examples include:

   • Raising finished floor levels above predicted flood levels.

   • Installing Sustainable Drainage Systems (SuDS) to manage surface water.

   • Incorporating flood storage areas to mitigate downstream risks.

   • Using flood-resistant materials and designing buildings to allow water to flow through without causing damage (flood resilience).

4. Document Findings: Submit a comprehensive report outlining risks, proposed mitigations, and compliance with planning policies. Highlight how the design ensures long-term safety and sustainability.

   
   

The UK Government’s FRA Guidance provides detailed instructions for preparing an FRA.