What Is a Soakaway?

A soakaway is a simple, but highly effective way of dealing with surface water runoff. It’s found primarily across the UK within our gardens, driveways and around homes. Essentially, a soakaway is a pit or void in the ground that is filled with rubble or modular crates that allow the rainwater to drain away into the surrounding soil gradually.

This helps to prevent overloading the public sewer network and makes soakaways the cornerstone of sustainable drainage systems (SuDS). They can help to prevent flooding, recharge groundwater and, helpfully, they comply with Building Regulations.

At Express Drainage Surveys, we want to help you understand all the elements of drainage systems that your property might feature. That’s why we’ve created this article, explaining what soakaways are, how they work and how to maintain them. We’re always here to help bring you peace of mind, and compliance with our professional drainage surveys should you ever need us.

What is a soakaway?

You can describe a soakaway as an underground system for collecting surface water and dispersing it into the ground around it. That means it collects any of your typical run-off from the roof, patio or driveway.

The principle is fairly simple: rather than allowing rainwater to flow and overwhelm the sewer system in a deluge, it instead gets diverted to a void to be slowly released back into the earth underground.

Traditional soakaways were essentially pits of broken rubble, stone or coarse gravel. This created a void space between the solids, which filters the water through slowly. Today, the modern alternative is plastic soakaway crates or geocellular units, wrapped in a membrane to stop soil ingress, acting as a filter in the same way as the traditional stone method.

Here in the UK, we use soakaways most commonly for managing just surface water. They are not suitable at all for foul water or sewage, which requires separate treatment. In fact, Building Regulations Part H states that new developments should, wherever possible, prioritise surface water infiltration before discharging to a sewer (which essentially points to soakaways).

Why soakaways matter in the UK context

We’re no strangers to heavy rainfall in the UK, with flash flooding becoming more common, especially with regard to surface water. The more urban areas we create, the more impermeable surfaces there are, such as tarmac and concrete, which means less natural filtration of rainwater into the ground.

Soakaways, therefore, are vital in the UK for:

Preventing gardens and driveways from becoming waterlogged.
Reducing the demand on our already stretched sewer system.
Supporting a more sustainable water management system for the future.

Remember, soakaways in the UK are only permitted for clean water. If you discharge untreated wastewater in a soakaway, not only are you acting illegally, but it’s very harmful for the environment. For any foul water, you can turn to septic tanks or sewage treatment plants instead.

Types of soakaway systems

Traditional rubble soakaways: These are simple pits filled with rubble and/or gravel. They are cheap and straightforward to create, but are prone to building up silt, so they have a shorter lifespan.
Plastic crate soakaway: Using modular, specially engineered crates, you get large void spaces and predictable performance from this system. The geotextile wrap will help to filter silt, making it more of a long-lasting effort.
Soakaway chambers or boreholes: Much rarer, and requiring greater regulatory approval, a borehole soakaway can be used to discharge surface water deeper underground. This is a specialist option.

How does a soakaway work?

You will have noticed that water collected from your roof gutters, downpipes and surface-level drains gets carried away, but where? Usually, it goes to the sewage system, but in a downpour, this can overwhelm things.

Instead, with a soakaway, the water passes through a silt trap or filter before entering the soakaway chamber, where it is stored temporarily. Over time, the surrounding ground gradually absorbs this water naturally. The rate of reabsorption can vary depending on the soil type – clay soils can take much longer than sandy or loamy soils.

The benefits of soakaways

Soakaways are becoming more popular in the UK, and it’s no wonder when they present some of the following key benefits:

They reduce the pressure on our sewers by diverting rainwater away from the main system, helping to prevent overflow and sewer flooding.
They reduce the risk of localised flooding and pooling, protecting homes, gardens and other property.
They are a more sustainable way of returning water to the ground, replenishing groundwater levels.
They are generally cheaper to install and maintain than piped solutions, making them a cost-effective option in certain areas.
They are discreet and unobtrusive, since they are buried underground, leaving no visual impact when looking at your landscape.

The limitations and risks

Now that we’ve looked at the benefits and advantages, let’s look at some of the reasons soakaway may not be suitable. Limitations include:

The soil type in your ground will have an impact – clay soil drains poorly, so makes it less effective with a soakaway.
There is a risk of blockages if you don’t have a silt trap, causing the system to clog.
A soakaway cannot be installed too close to a property, as water may seep towards foundations – this means plenty of land is required.
Inappropriate or unpermitted soakaway use could leave you liable for costly remediation.

How to maintain a soakaway and best practice

With all of the above in mind, keeping your soakaway in good condition is critical. While they are low maintenance, here are three things you can do to ensure their longevity:

Inspect and clean silt traps to prevent a build-up of sediment from getting into the pit.
Check for any pooling or slow drainage around downpipes, which may indicate a blockage.
Keep roots and vegetation away from your soakaway to avoid them penetrating the structure.

If you need expert drainage services from a team you can trust, look no further than Express Drainage Surveys. We can provide detailed surveys of your existing system to help you assess any blockage or locate damage when you’re faced with overflowing drains or a waterlogged garden. Our drainage services include: