The soil beneath our feet could be the missing piece in urban flood protection.

Surface-water runoff is becoming a bigger challenge for UK development as rainfall becomes more intense. This is supported by research which has shown that healthy, biologically active soil can dramatically improve infiltration, helping water soak into the ground rather than becoming runoff - so why are we ignoring one of the most effective tools for managing that water may already be beneath our feet, writes Pete Thomas  at Ruskins the tree and soil specialists
The Met Office reports that the UK has become wetter over recent decades, with the period 2011–2020, 9% wetter than 1961–1990. Six of the UK's ten wettest years since records began in 1862 have occurred since 1998, while rainfall events exceeding 50mm have also become more frequent. 
That challenge is set to grow, with the Met Office projecting that summer rainfall events that currently occur once every two years, could become around 25% more intense, increasing the risk of surface-water flooding, particularly in urban areas. That changes the way we need to think about Sustainable Drainage Systems (SuDS).
Modern SuDS are designed to mimic natural drainage, slowing water by reducing runoff and encouraging infiltration wherever ground conditions allow. England's national SuDS standards, introduced in 2025, specifically prioritise infiltration to ground and require developments to manage at least the first 5mm of rainfall from the majority of rainfall events without it becoming runoff to surface waters or piped drainage systems. However, achieving that depends on more than the visible drainage infrastructure. It depends on the ground.

A beautifully designed rain garden, swale or infiltration feature cannot perform as intended if the soil beneath and around it has been compacted, degraded or stripped of its biological function.

Soil can be part of the solution
An EPA-funded study, Infiltration Through Disturbed Urban Soils and Compost-Amended Soil Effects on Runoff Quality and Quantity, found that adding compost to disturbed urban soils increased infiltration rates by 1.5 to 10.5 times compared with unamended soil at the study sites. The research was published in 1999, so the figure should not be treated as a universal performance guarantee. It does, however, demonstrate the potential impact of improving degraded urban soil. 
The principle remains highly relevant today because the condition of the soil can determine how much rainfall enters the ground and how much becomes surface runoff. That matters even more as rainfall intensity increases.

Construction activity in particular, can severely disturb soil structure. Heavy machinery, storage of materials, repeated trafficking and inappropriate soil handling can compact the ground, reducing the pore spaces through which water and air move. This can create a strange contradiction in a development, where significant investment goes into engineered drainage infrastructure while the surrounding soil has been left poorly equipped to absorb water.
The answer is not to replace engineered SuDS with soil. It is to make soil, vegetation and engineered drainage work together. This is because the 2025 national standards explicitly call for SuDS to be integrated throughout the development and landscape, creating healthy and resilient spaces for people and wildlife. 

Every garden can contribute
Verges, parks, public open spaces, front gardens and rear gardens collectively represent a significant area of urban landscape. Healthy soil in these spaces can help intercept rainfall, support vegetation and reduce the amount of water reaching hard surfaces and drainage networks. That creates a distributed approach to water management.

Instead of asking one attenuation basin or drainage feature to deal with rainfall after it has travelled across the development, the landscape can help manage water closer to where it falls. This is particularly important because, as already mentioned, the new national standards require consideration of everyday rainfall as well as extreme events.

Additionally, rainfall absorbed by soil percolates into aquifers, not the urban drainage system.
There is another reason to take soil seriously. Healthy soil is alive, with bacteria, fungi, earthworms and other soil organisms helping to create and maintain soil structure, cycle nutrients and support plant growth. Those biological processes influence how water moves through the ground and how successfully vegetation establishes. That makes soil biology relevant to biodiversity as well as drainage.

A newly planted landscape may look successful when it is completed, but its long-term performance depends partly on what is happening beneath the surface. If the soil is biologically depleted or compacted, vegetation may struggle to establish, require greater intervention and become less resilient during periods of drought or intense rainfall.

The UK Government's SuDS standards recognise this connection, requiring drainage systems to deliver benefits for water quality, biodiversity and amenity alongside flood management.

Biodiversity starts below ground

Biodiversity Net Gain has rightly increased attention on habitats, planting and ecological value. Soil, however, is often less visible in those discussions, mainly because the ecosystem begins beneath the surface, where it remains hidden.

It cannot be ignored because healthy soil supports all life above it, which in turn support insects and other wildlife, while soil organisms themselves form a complex ecosystem. Protecting and restoring soil biology therefore has the potential to support several objectives at once - water management, vegetation establishment, biodiversity and landscape resilience. For developers, that creates an opportunity to think differently about what happens to soil during construction.
There is also the benefit of healthy soils, that increases in-line with improve biodiversity, its ability to hold Carbon also increases.  This improvement (in biodiversity and Carbon ) can be measured. 

There is no doubt that the climate is changing. Rainfall is becoming more intense, urban areas are becoming increasingly pressured and the expectations placed on SuDS are increasing. That means that the response cannot be based entirely on bigger tanks, deeper basins and more engineered infrastructure. We need to make the ground itself part of the solution.

At Ruskins, we believe soil should be considered alongside drainage, planting and biodiversity from the earliest stages of development. Understanding its condition, protecting good soil and restoring damaged or compacted ground can help create landscapes that manage water more naturally and support healthier vegetation.
The future of urban drainage may therefore depend on something that is easy to overlook, but all you have to do is look beneath your feet. There is an entire drainage and biodiversity system already there.