If you live in the UK, we’re sure that you’re aware of how wet and rainy our weather can be. Even in the summer, there’s often a threat of flooding from excess rainfall, especially for properties located close to rivers or other bodies of water. This is where soakaway boreholes can come in handy.
You may not have heard of a soakaway borehole before, but these simple systems are highly effective. They perform the vital role of draining excess water, which can be reused elsewhere rather than damaging the surrounding area – making them ideal for areas that experience heavy rainfall.
For landowners of any kind, whether private or commercial, a borehole soakaway could be the solution to persistent surface drainage problems. As providers of a soakaway borehole drilling service, the team at Teckna Group wants you to understand just how helpful these systems can be – which is why we’ve answered some frequently asked questions about soakaway boreholes below.
What is a soakaway borehole?
Also known as a deep bore soakaway, this is a drainage system installed beneath the surface of the ground. It collects excess water from the surface to keep the ground in good condition.
These excavations use void-forming materials – such as bricks or crates – to collect and trap the water and then redirect it, allowing the water to ‘soak away’ into the surrounding land.
Once the sealed storage chamber gathers the water, it transports it deeper into the ground, where it’s subsequently filtered into the surrounding soil or permeable strata and used more effectively.
Soakaway boreholes are often used in locations not connected to a nearby body of water or man-made drainage system, or where an existing drainage system is failing to cope with surface water.
A soakaway is essentially a reverse well, which loses water rather than continually storing it. These infiltration devices are considered Sustainable Drainage Systems (SuDS), because they deal with the problem of excessive run-off at the source rather than diverting it to other over-used systems.
What’s the difference between a conventional soakaway and a soakaway borehole?
The main difference between borehole soakaway options is their depth. A conventional soakaway sits closer to the surface. It’s constructed by digging a small hole, then inserting a cylindrical chamber with perforations or filling it with rubble, which allows the water to drain into the soil.
As the alternative name ‘deep bore soakaway’ suggests, this type is inserted much deeper into the ground. When the permeable stratum is covered by impermeable soils, the soakaway will need to be installed further down where the ground is porous enough for the water to drain effectively.
With a borehole soakaway, the water is collected in a kind of storage chamber, then transported further into the ground through a small plastic or steel pipe that may be partially perforated.
When a shallow traditional soakaway is installed within fissured strata, there’s a greater risk of the ground being inundated with seeping water and therefore sinking in. By contrast, a soakaway borehole discharges run-off into deeper fissures in the soil, reducing the risk of subsidence.
It can be very expensive to install a soakaway that doesn’t work properly, which is why it’s so important for professionals to investigate the geological properties of the site.
At Teckna Group, we have considerable experience in soakage testing, carrying out percolation tests on the soil to determine its permeability. We can drill and install both conventional soakaway designs and borehole soakaways with a finished diameter of 6” (unless otherwise specified).
What are the benefits of using a soakaway borehole?
When geological conditions are poor or a traditional drainage system is incompatible or too expensive to install, a borehole soakaway is a cost-effective alternative. It can efficiently collect and drain surface water, keeping the soil moist to encourage growth while avoiding over-saturation.
This also helps to prevent significant damage from waterlogging or flooding. Without appropriate drainage, excess water can build up and stagnate, either flooding the area or causing the ground to sink in on itself – which can cause significant problems for the foundations of nearby buildings.
While soakaways are most often used in rural areas without storm drains or other such systems, they can be installed anywhere with suitable ground conditions. This includes suburban homes with waterlogged gardens, or businesses from local councils to outdoor sports and leisure facilities.
Anywhere with high levels of rainfall and inadequate surface drainage can benefit from a soakaway, as they’re practically invisible once installed and easy to maintain. Other than regular checks for silting, contamination, or plant roots, you can simply leave your soakaway borehole to do its job.
Lasting for at least 25 years with minimal interference, protecting your property against the costly repairs and replacements associated with water damage, and visually discreet enough to not be an eyesore – there’s no reason not to install a soakaway if you’re in need of an anti-flooding solution.
How does a soakaway borehole work?
As mentioned above, soakaways are essentially a buried form of water storage, which temporarily collect surface water and then allow it to infiltrate the deeper layers of soil around them. They redirect and filter excess water in a gradual and controlled manner to prevent water ingress.
They must be well-designed and large enough to ensure that they discharge any stored water quickly, maintaining the capacity to handle the volume of water from the next rainstorm.
When there is a thicker and less permeable layer of soil, it’s necessary to drill a deeper soakaway borehole to reach more permeable layers. This ensures that the surface water can drain effectively.
Soakaway construction involves excavating the ground and installing a formal structure, such as a ring of concrete, a fabric membrane, or plastic crates. Traditionally, the soakaway storage system would contain stones and rubble, but modern geocellular structures are becoming more popular.
The size of a workable soakaway depends on several factors, including the square meterage of the area that requires drainage, the porosity of the ground, and the average rainfall in that location.
The bigger the area that needs to be drained, the larger and more comprehensive the soakaway system must be. The shape and size will depend on the particular site, but installations generally follow national Building Regulations, guidance from local councils, and the CIRIA SuDS Manual.
How do you install a soakaway borehole?
The installation process for a rainwater soakaway borehole is very similar to that of a water borehole, beginning with an initial assessment of the geological properties of your site.
A percolation test will determine whether your soil is suitable for water drainage, while the general site assessment will inform the design suitability and installation costs. This will include checking for pipes and cables, and carrying out any necessary preparation such as removing stones and roots.
Once the project is outlined, materials procured, and the site prepared, we then use rotary air and mud drilling techniques to dig a hole to a specified depth. We insert a suitable liner and filler to capture and discharge water, then secure the system with grouting to seal it where necessary.
A permeable membrane will help to filter silt and potential contaminants from the water before it soaks into the surrounding soil, and perforated pipes will deliver the water to deeper layers.
If required, we can also install land drainage features like siphon heads, guttering, downpipes, and gullies to aid with directing run-off from your property towards the soakaway. After completing the installation, we’ll conduct another percolation test to check that the system is in working order.
Generally, you can expect this process to take 10-15 working days, but how long it takes to drill a borehole depends on the site and the type of system being installed. For example, a water borehole for procuring potable water will take much longer to install than a soakaway borehole for drainage.
What makes a suitable site for a soakaway borehole?
The first thing to consider when choosing a suitable site for a soakaway is the water table. This is the saturation line or upper level of groundwater within the soil or bedrock, which can rise during rainy seasons and fall during dry spells.
If the water table is too high, then a soakaway simply won’t work there. It will just become a hole full of water – called a sump – because the ground is already so saturated that there’s nowhere else for the water in the hole to go.
However, if the water table is high due to an impermeable layer, then digging down to the more permeable sub-strata could make a borehole soakaway possible. The depth and diameter will depend on the height of the water table at that level and the volume it needs to process.
This is why soakage tests are required to detect the soil infiltration rate and its drainage capacity. Hard rocks, such as granite or basalt, and heavy soils like clay are not suitable for soakaways. Porous sub-soils (e.g. sandy loam) and permeable bedrock like sandstone or chalk offer the best conditions.
Soakaways are normally only suitable for draining areas smaller than 100m2, but they can be used to drain any area as long as the soakaway can empty at least half its contents within 24 hours. At least 1m of clearance between the soakaway base and groundwater level will help to prevent rising water from compromising its capacity and reducing the amount of unsaturated material.
Do you need planning permission for a soakaway?
Though the ground’s geology and stability are the determining factors for the suitability of a soakaway site, you also need to take location restrictions into account. The Building Regulations for soakaways are covered by Approved Document H – Drainage and Water Disposal (2015).
Possibly the most important distinction is that it’s now illegal to use a soakaway to drain sewage. They’re only allowed for draining rainwater and surface water, protecting the soil and groundwater from pollutants that can also contaminate nearby water sources.
If you do have a sewage drainage field or a septic soakaway, then you must ensure that your rainwater soakaway is sited far away enough to avoid contamination and over-saturation.
Aside from avoiding pollutants, a permitted soakaway site must be at least 5 metres away from any buildings to avoid saturating the foundations. It must be at a lower point compared to the area that requires draining, and also at least 5 metres from the property boundaries and any roads.
The proposed soakaway borehole must meet the drainage standards for soil infiltration and storage emptying. This includes the distance of at least 1m from the bottom of the construction to the top of the groundwater level, at any time of year, to avoid exceeding the ground’s soakage capacity.
Contact Teckna Group for soakaway borehole drilling
Hopefully, this borehole soakaway guide tells you everything you need to know about these flood-prevention devices. Should you still have questions about soakaway boreholes and how they could benefit you, or whether they’re suitable for your land, feel free to get in touch with our team.
At Teckna Group, we have many years of experience in soakaway site surveys and soakaway borehole drilling. Why not call us on 01257 421 700 or email enquiries@tecknagroup.co.uk and let us solve your water drainage problems? We’ll be happy to share our expert solutions with you.
