What are ‘spongy landscapes’ and how do they reduce flood risk?

It starts with how rainfall lands on the ground. In many areas, spongy landscapes play a crucial role in absorbing and retaining this water.

The idea of a “spongy landscape”, used in recent research from the Chartered Institution of Water and Environmental Management (CIWEM), is simple enough. Some landscapes absorb, store and slowly release water. Others shed it quickly. The difference matters.

CIWEM is influential in flood risk, drainage and environmental practice, as explored in the role of CIWEM in environmental management and planning. Its spongy landscapes report focuses on farming and land management, but the wider point is relevant to anyone thinking about flooding: water behaviour is shaped by the landscape before it is shaped by a pipe, culvert or defence.

That is becoming more important as rainfall patterns change. Heavier rainfall and wetter catchments are already altering flood behaviour across the UK, as discussed in how increasing rainfall is changing flood risk in the UK.

What is a ‘spongy landscape’?

A spongy landscape is land that can absorb, slow and filter rainfall.

Instead of rainwater running straight off the surface, it is held in soils, vegetation, wetlands, ponds, ditches and floodplains. Some water infiltrates. Some is temporarily stored. Some is released gradually back into rivers and groundwater systems.

That delay is the point.

When water moves too quickly across land, it reaches rivers and drains at the same time. Flows peak faster. Drainage systems are placed under pressure. Flooding becomes more likely.

This is closely connected to pluvial, or surface water, flooding, where rainfall overwhelms the ground, drainage systems or local flow routes before it ever reaches a main river.

How landscapes become ‘spongy’

Sponginess is not created by one feature. It comes from how soils, vegetation and water storage work together across a catchment.

Soil health and water storage

Soil is central to the whole idea.

Healthy soil contains pore spaces that allow water to soak in and move through the ground. Compacted or degraded soil does the opposite. It sheds water.

CIWEM’s report gives a useful example from the North East Cotswolds. Modelling suggested that changes in land management across the catchment could store around 2 million cubic metres of additional water and reduce flood peaks by about 21% for a 1 in 2 year flood event.

That is not a marginal benefit. It shows why soil condition is directly relevant to flood risk, not just agriculture. We have explored that link separately in how soils influence flooding and resilience.

Vegetation and land management practices

Vegetation helps protect soil structure.

Cover crops, herbal leys, reduced tillage and managed grassland all help reduce compaction and increase infiltration. They also slow the movement of water across the land surface.

The effect is not dramatic in the way a flood wall is dramatic. It is quieter than that. But across a catchment, small delays matter. If less water arrives at the same time, peak flows are reduced.

Natural flood management features

Spongy landscapes also use physical features that hold or slow water.

These can include wetlands, leaky dams, floodplain reconnection, ponds, woodland planting and restored river corridors.

These are all forms of natural flood management. They do not remove flood risk entirely, and they do not work equally well everywhere. But in the right place, they can reduce downstream flood peaks and provide wider benefits for water quality, biodiversity and drought resilience.

That wider context is covered in natural flood management and how it works in practice, with more technical detail in Environment Agency research into natural flood management.

How spongy landscapes reduce flood risk

The benefit comes from changing the timing and volume of runoff.

Slowing runoff at source

The first effect is simple: more water is held where it falls.

That reduces the amount of rainwater rushing into streams, rivers, road gullies and surface water sewers during the most intense part of a storm.

This is the same basic principle behind source control in drainage design. We have discussed this before in why flood risk is often a scale problem rather than a drainage problem. The spongy landscapes concept applies that logic beyond the development site and out into the wider catchment.

Reducing peak river flows

CIWEM’s report includes modelling from Spains Hall Estate in Essex. It found that a “whole farm reservoir” approach could reduce peak flood flows by 15% to 30%.

That matters because flood damage is often driven by peak conditions. A small reduction at the right moment can affect whether water remains within a channel, overtops a bank or overwhelms downstream drainage.

Increasing distributed water storage

The Spains Hall work also suggests that land management changes could provide around 5,942 megalitres of storage. CIWEM compares that to about 12% of the planned Fens Reservoir.

That is a useful comparison because it reframes the issue. Storage does not always need to mean one large engineered structure. It can also mean thousands of smaller storage points spread across soils, fields, wetlands and flow pathways.

Smaller features matter too. Sediment ponds and on farm water storage can slow runoff and improve water quality, as shown in research on sediment ponds and flood control.

Supporting drought resilience and baseflows

Spongy landscapes are not only about flooding.

The same Spains Hall modelling found that the approach could increase downstream summer flows by 5% to 10%. That is because water held in soils and landscape features can be released more slowly during dry periods.

This is one reason the concept is getting attention. It is not just a flood risk idea. It is also about drought, water resources and long term catchment resilience.

How this relates to SuDS and drainage design

There is a clear link between spongy landscapes and Sustainable Drainage Systems.

At site level, SuDS aim to reduce runoff, manage water close to where it falls and mimic natural processes. These principles sit behind the 2025 National Standards for Sustainable Drainage Systems.

Spongy landscapes apply similar thinking at a bigger scale. Instead of asking only how a site drains, they ask how the wider land system stores and releases water before it reaches the site at all.

That connection between natural processes and designed drainage is explored further in Green SuDS and nature based drainage approaches in planning.

Why spongy landscapes are gaining attention

The renewed interest is not hard to understand.

The UK is dealing with heavier rainfall, ageing drainage infrastructure, drought pressure and rising expectations around water quality. At the same time, many flood risk problems cannot be solved only at the point of impact.

Land use is part of the answer. CIWEM’s report sits alongside a wider policy direction towards catchment thinking, natural flood management and better use of land for water storage. That is also reflected in the England Land Use Framework and its implications for flood risk and planning.

What this means for flood risk and planning

Planning still assesses flood risk at site level. That will not change.

But site level risk is shaped by wider catchment behaviour. Upstream land management affects runoff rates, flood mechanisms, drainage performance and the timing of peak flows.

For developers, planners and landowners, the point is not that spongy landscapes replace flood risk assessments, drainage strategies or engineered defences. They do not.

The point is that flood risk cannot always be understood properly by looking only at the red line boundary. Water arrives from somewhere. How it gets there matters.