Put simply, surface water flooding happens when more rain falls than the existing drainage systems — or the ground itself — can absorb. The water then lies on the surface and begins to flow, causing localised floods that can affect your development.
Surface water flooding is typically caused by the volume of rainfall and the speed at which it hits the ground. This creates a build-up that the existing drainage systems simply cannot cope with.
These flood events usually have localised effects, so they often only impact properties close to the resulting floods, and sometimes only for a short period. However, because surface water flooding is so sudden and intense, the damage can be extensive — affecting large areas and lasting for prolonged periods.
So we know surface water flooding can be hugely disruptive to a new development. Now let’s look at how it could affect you and your future planning applications, and what you can do to prepare. Read on to learn more.
Which Flood Zones Does Surface Water Flooding Affect?
You might assume that surface water flooding only affects Flood Zones 2 and 3, and that you don’t need a Flood Risk Assessment if your site sits outside these zones.
However, surface water flooding caused by insufficient drains or critical drainage problems will also affect Flood Zone 1 developments.
Critical Drainage Areas (CDAs) are specific areas within Flood Zone 1 that have been identified as having inadequate drainage infrastructure. These areas are at critical risk of failing during flash floods, where run-off can cause a range of problems. If your site lies within one, you will still need to carry out a Flood Risk Assessment.
So even if your development is in Flood Zone 1, surface water flooding can still heavily affect it, thanks to its inconsistent and unpredictable nature.
Did you know? Following the Environment Agency’s updated National Flood Risk Assessment in December 2024, around 4.6 million properties in England are now in areas at risk of surface water flooding — compared to roughly 2.7 million at risk from rivers and the sea. Surface water is now the most common source of flooding in England. These figures may surprise you, but they highlight why extra vigilance matters when you prepare a planning application.
Identifying and Preventing Surface Water Flooding Risk
To check whether your site is at risk of surface water flooding, visit the government’s flood risk service on gov.uk and navigate to the surface water section. As of March 2025, the Environment Agency’s updated Flood Map for Planning also displays surface water risk for the first time, making it easier to assess your site.
To identify your risk further, you can contact your Lead Local Flood Authority (LLFA). Their role is to manage local flood risk, including surface water, groundwater, and rivers and streams that aren’t classed as main rivers.
So what can you do to reduce the risk? There are several effective measures:
- Sustainable Drainage Systems (SuDS)
- Natural flood management (NFM)
- Property flood resilience (PFR) measures
- Reporting any blocked highway gullies, footpaths or drains to your County Council or Unitary Authority
The Rising Cost of Surface Water Flooding
Surface water flooding already causes hundreds of millions of pounds of damage in England each year, and that figure is set to rise. With a growing population, increasing urbanisation and more frequent heavy rainfall driven by climate change, the risk is increasing year on year.
The scale of the challenge is significant: the Environment Agency now estimates that by the mid-century, around 1 in 4 properties in England could be in an area at risk of flooding from rivers, the sea or surface water. While you can monitor and reduce surface water flood risk, it’s essential to plan for it early.
If your site is in Flood Zone 1 and you’d like to find out more about our approach to Flood Risk Assessments — or whether you need one for your site — reach out to a member of the Nimbus team today. We’re always happy to help.
About Nimbus Engineering
Nimbus Engineering is a dedicated team of consulting Civil Engineers with extensive experience across all aspects of flood risk and drainage design. Our work includes Sustainable Drainage Systems (SuDS) design, Flood Risk Assessments (FRAs), Flood Warning and Evacuation Plans (FWEPs), and surface water management schemes, including SuDS reports.
We work with you from the planning stage right through to construction, and we provide the necessary SuDS management and maintenance plans. That means you get tailored support every step of the way.
We work closely with many Local Authorities and Lead Local Flood Authorities nationwide, so we understand each one’s specific requirements — particularly when it comes to SuDS reports and drainage strategy reports.
