Do I Need a Flood Risk Assessment for a Major Development?

What Is a Major Development?

For flood risk and water management purposes, a Major Development is defined differently for residential and non-residential projects.

A residential major development involves either ten or more dwellings or development on a site of 0.5 hectares or larger. Non-residential major developments consist of either 1,000 square metres or more of construction or development on sites exceeding one hectare.

Due to these size thresholds, planning applications for major developments consistently require two water-related documents: a Flood Risk Assessment and a Drainage Strategy.

What Flood Risk Assessment Do I Need for a Major Development?

A Flood Risk Assessment for major development applications must evaluate environmental site constraints against proposed plans using quality data. “A flood risk assessment using good data allows for better decision-making and sometimes saves time and money on a project.”

The assessment should determine whether the development design complies with policy requirements and identify necessary mitigation measures or layout adjustments for planning approval.

Major developments in flood-prone zones present multiple risks: the development itself may face hazard exposure, or construction could displace flooding onto neighbouring properties. Assessments must verify the site’s suitability for its intended use through the Sequential and Exception Tests required by the National Planning Policy Framework.

How Aegaea Can Support Your Flood Risk Assessment

Aegaea’s team offers early-stage consultation on site development potential, reviewing both brownfield and greenfield locations. Engaging flood risk expertise before finalising master plans helps identify constraints and recommend mitigation strategies that enhance planning acceptance while ensuring safe, viable development.