From unknown to action: tackling groundwater flood risk in planning policy

Fola Ogunyoye is Placemaking (Planning) Workstream Lead, at Project Groundwater

Why groundwater flood risk is England’s silent threat

When we talk about flooding in England, most people think of rivers bursting their banks, coastal surges, or surface water pooling after heavy rain. And with good reason – The Environment Agency’s National assessment of flood and coastal erosion risk in England 2024  confirms that 1 in 6 properties in England is currently at risk from these sources, a figure projected to rise to 1 in 4 by mid-century.

But there’s another, often overlooked flood risk – groundwater flooding.

Groundwater flooding happens when too much water gathers beneath the ground, causing the water table to rise to the surface, or close enough to affect underground rooms or infrastructure such as basements, cellars, drainage pipes and sewers.

Unlike other types of flooding, groundwater flood risk remains a big unknown. It’s rarely considered in local planning policy, strategic and local allocations, or in development management. In many cases, it’s identified so late in the planning process that only relatively ineffective “sticking plaster” solutions remain - such as pumping during high groundwater instead of avoiding at risk areas.

What makes groundwater flooding so challenging?

Groundwater flooding is tricky for several reasons:

• You can’t see it coming 
  It’s invisible until water emerges from the ground and by then, it’s too late.
  
  
• It’s less frequent, but more persistent
  While surface water, river and coastal flooding may last hours or days, groundwater flooding can linger for weeks or even months.
  
  
• It’s delayed
  It can occur days or weeks after single or multiple storms, making the link to rainfall less obvious.
• It’s hard to defend against
  Groundwater rises over vast areas, making defence against it costly and challenging. Even before reaching the surface, it can flood basements, damage underground infrastructure, and infiltrate drainage and sewer systems.

The result? Planners can’t plan for resilient communities, developers struggle to assess viability, opportunities and constraints as early as possible, and people aren’t able to live in flood resilient homes.

The planning blind spot: why groundwater flooding gets missed

Despite the Environment Agency’s strategic role in flood risk management, there’s no freely available national groundwater flood risk data comparable to river, sea or surface water maps. Worse, there’s no statutory consultee for groundwater flood risk in the planning system.

This lack of clear responsibility leads to reduced visibility and understanding of groundwater flood risk, meaning it gets missed and consequently that means no dedicated funding or resources to deliver the role – creating a vicious cycle.

With the government’s ambitious growth targets, it is important that we avoid creating future problems by ensuring new communities are planned and built to be safe, resilient and adaptable to flood risk and climate change.

What needs to change?

Government action:

• Identify and assign clear responsibilities for groundwater flood risk – similar to river, sea and surface water - within the planning system.
• Include groundwater flood risk mapping into the Flood Map for Planning.

Local action:

While that’s underway, Local Authorities, developers, planners and others should:

• Use available guidance like the TCPA and RTPI Planning for the Climate Crisis
• Have clear groundwater flood risk mapping, risk information and developer guidance within Strategic Flood Risk Assessments (SFRAs).
• Embed clear and explicit policies on groundwater flood risk within spatial development strategies, local plans, neighbourhood plans, supplementary guidance etc.

Making space for groundwater: The 4As 

Finally, there should be development of guidance to support a “Making space for Groundwater” approach in development planning through the 4As hierarchy:

• Assess – Assessing and understanding all flood risk, including groundwater.
• Avoid – Avoid development in areas with groundwater flood risk if possible.
• Adapt – If can’t avoid, adapt development to make space for groundwater.
• Accommodate – If can’t avoid and adapt, accommodate groundwater safely within development without affecting safety and function.

At Project Groundwater, we’re developing guidance under our Planning Workstream to support this approach - due for publication later in 2026. Stay updated via the Project Groundwater Website, our Project Groundwater Newsletter and follow us on LinkedIn, Facebook and X.

The bottom line: building resilient communities starts now

Groundwater flooding may be out of sight, but it shouldn’t be out of mind. By addressing this hidden risk early in planning, we can build communities that are safer, more resilient, and ready for the challenges of climate change.