From next year property owners must manage surface water to reduce flood risk, erosion, and environmental damage under UK law.
A key part of this is the use of sustainable drainage systems, often shortened to SuDs, a term for a set of environmentally-friendly techniques that are designed to help manage and control surface water runoff, particularly in urban areas.
Soakaways for driveways are an example of a SuD that can help homebuilders meet the legal requirements.
What is a soakaway for a driveway?
Property flood resilience champion Mary Long-Dhonau OBE – AKA ‘Flood Mary’ – says a driveway soakaway is essentially a drainage system that is designed to prevent surface water runoff in the event of heavy rain. While a soakaway can be built anywhere in a garden, adding one to a driveway is particularly sensible to prevent any surface water potentially flooding the area and any vehicles and belongings on it.
“There are various ways a soakaway can be made, such as using the rigid plastic ‘honeycomb’ like structures, which are filled with coarse gravel or similar. This allows rainwater to soak through to the ground, rather than run-off onto the surrounding highways," Mary Long-Dhonau explains.
“While there are similarities with regular soakaways, the main difference is that [soakaways for driveways] must allow for heavy vehicles to park on them with no degradation, so they need to be constructed using the right methods and materials.”
SuDS (sustainable drainage systems) takes into account a combination of methods, from ponds, swales, and soakaways to tree pits, permeable paving and water harvesting, to name just a few. The aim of SuDS is to mimic natural water management processes by allowing water to infiltrate into the ground, evaporate away, or be stored again for later use, rather than immediately diverted into traditional drainage systems.
“The good news is it is perfectly possible for all developers and homeowners to incorporate SuDS to help make a difference," says Mary Long-Dhonau. “Another is permeable paving, which essentially looks and acts like normal paving but when rain falls, it can easily soak through."
How big does a soakaway need to be for a driveway?
The size of your soakaway for your driveway will depend on the rainfall in your area, your soil's water retention as well as the size of your driveway. A percolation test will give you a good idea about how quickly your soil absorbs water and is therefore a vital first step before building a soakaway.
Mary Long-Dhonau explains: “[The size of your soakaway] will vary depending on a number of factors, including the size of your driveway area, number of vehicles that will use the space, and the current flood risk level facing the property in question.
“My advice would be to speak with your construction contractor, civil engineer or a local flood risk surveyor who can provide specific advice based on your situation, while taking into account any local planning regulations.”
Usually soakaway crates, such as this COREwater SoakAway/Attenuation Crate from Amazon, are stackable so you can buy the quantity you specifically need for the size of soakaway you are building. When it comes to soakways for driveways you will need to double check that they can withstand the weight of the vehicles too, for instance several of these soakaway crates on Drainage superstore are suitable for driveways, like this robust Graf rain soakaway crate that is rated for 60 tonnes and considered perfect for residential soakways.
Do I need planning permission to install a soakaway in my drive?
While installing a soakaway itself would not need planning permission, installing a driveway often does need driveway planning permission when permitted development rights do not apply. Therefore when installing a soakaway for a driveway you may end up needing to include the details of this in your planning application.
Mary says: “You need planning permission to lay a brand new driveway, however your local authority will look favourably on any moves you take to remove surface water flood risk.
“In general, it’s essential to check with your local planning authority as the need for planning permission may also vary depending on your specific location, local regulations and scope of the work. For example, the property may be in an Area of Outstanding Natural Beauty and therefore rules may be tighter on what you can or can’t do.”
How to install a soakaway for a driveway
A soakaway is in its most basic form a hole dug into the ground, which is then filled with rubble or — more ideally these days — specialist soakaway crates. This allows surface water additional space to percolate back into the earth in a measured way. The process is laid out in-depth in our how to build a soakaway article but essentially involves digging a large hole in the ground and stacking soakaway or attenuation crates within it. The crates feature voids, allowing large volumes of water sufficient surface area to seep back into the ground.
You ideally want to use permeable paving or gravel as a driveway surface to allow water to soak through into the ground and soakaway beneath it.
Mary adds: “The installation process for a driveway soakaway typically involves a number of steps, however I advise that you always consult a professional engineer or contractor experienced in drainage to ensure the site is assessed correctly and the excavation, material and final permeable surface is appropriate for your location and the type of soil/subsoil your area has.
“There is no one rule for all areas. Also remember that once a driveway is installed you should ensure the soakaway is inspected and maintained periodically, to make sure it is functioning correctly.”
