What is a rainwater soakaway?

What is a rainwater soakaway

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Here in the UK, it is crucially important to have a soakaway, also known as a French drain, installed to address both sewage drainage system functionality and surface water runoff. Rainfall is simply an accepted and undeniable part of living in the UK but the charges that come from the accumulation of rainwater that drains from your property are never fun to receive. With this in mind, what exactly is a rainwater soakaway?

A rainwater soakaway is a drainage trench that is dug from surrounding soil in order to manage surface water through a septic tank or and alternative drainage route. Rainwater soakaways are usually made from gravel or stone or even plastic soakaway crates.

In this guide, we will look at what a soakaway is and how it relates to a septic tank, how a soakaway works when addressing surface water run off, who needs a soakaway, how to make a soakaway, and other related questions. So read on to find out all you need to know about rainwater soakaways.

How does a rainwater soakaway work for surface water drainage?

All buildings have drainage from the roof which catches the rainwater and brings it down a downpipe. But the rainwater and excess surface water has to go somewhere, and this is typically captured and filtered through a soakaway (French drain).

Soakaways are a good way to provide groundwater recharge and make for a more ecologically sustainable living environment. Those buildings that do not have access to a suitable public sewer or watercourse might often find themselves facing inconvenient water logging.

In order to prepare for the next storm or rain shower, there is a persistent need to drain the excess roof water away from the house. It is here that rainwater soakaways come into play due to their working principle of a reverse well that loses water instead of holding it in.

Since the soakaways drain out the water, they can be used in any situation- whether it comes to houses or highways- in order to reduce water logging. Overall, it is one of the simplest and most ecologically benefiting systems with a low environmental impact and little maintenance.

How big is a soakaway?

A soakaway should be large enough to ensure that surface water is draining correctly according to the overall drainage field in the surrounding ground.

The required size of a rainwater soakaway must be calculated to ensure that the soakaway is large enough to store the required runoff.

The required volume of water is calculated from the difference between the runoff entering the soakaway from a storm event of a particular duration, and the water which infiltrates into the surrounding soils during the storm event. This is one of the most important factors in a soakaway design.

The depth of the soakaway is also important to get right when sizing a soakaway. This is because the deeper the soakaway, the greater the surface area available for infiltration and the greater the volume available for storage.

The effect of larger diameter soakaways can be similar, but a deeper soakaway is much more effective at increasing the infiltration.

Additionally, a soakaway crate is affected by the same considerations, but as the void ratio in crates is so large it is often sufficient simply to size the soakaway to suit the storage volume required.

However, in many cases the storage volume provided in the annulus (circular path) is small compared to the storage chamber and can decrease over time due to sediments collecting from the runoff- this is after all a hole in the ground.

For this reason the storage capacity of the annulus area is sometimes neglected.

In short, the size of a soakaway should be large enough to hold the run off and not overflow the drainage system.

Who needs a rainwater soakaway?

Depending on various building regulations regarding your area’s drainage systems, having a soakaway is generally a good idea. If you are faced with the acute disadvantage of not having access to a proper watercourse, the next best option is investing in a soakaway.

For those who reside in areas that are prone to storm water, making sure that there is a soakaway installed is of crucial importance.

This is because the soakaway replenishes the groundwater which allows for a low environmental impact when installed correctly. Plus, a rainwater soakaway benefits the community as there is no threat of water borne diseases.

This type of drainage system is easy to install with the help of professionals, and this is advisable since a professional team such as KJC Drainage, can adhere to local building regulations regarding soakaways.

Despite its various advantages, there are some things that you should consider while installing the soakaway.

Even if you find that you have use for a rainwater soakaway, there are some things that you should keep in mind before considering installing one.

Always remember that a rainwater soakaway does not work on heavy clay soil in your garden. Therefore it is not suitable for your gardens and the outdoor lawn space if you have this type of soil.

Additionally, soakaways are not appropriate for polluted rainwater, especially following heavy rainfall. If you live in an area that has a lot of smog, it might not be a good idea to install a soakaway as it can increase the groundwater pollution levels.

Apart from these considerations, having a rain water soakaway is a good idea to manage surface water.

How do you make a rainwater soakaway from the surrounding soil?

The first step to installing a soakaway is to dig a hole deep enough to adequately hold the surface water. A three meter wide hole should do the job. Generally speaking, you do not need planning permission to make a soak away.

Soakaway Crates

rainwater soakaway crate

The best method to take is to use a soakaway crate system. To make a rainwater soak away, you will need to first excavate the soil by making a hole that is the right size for the crates and the top, side and base fillers of coarse stone and compacted sand.

You should receive some clips or ties with the soakaway crate. These are used to hook up the crates to prevent movement while the side-filling materials are added.

Always wrap the crates with a geotextile membrane to maintain the performance of the system.

A layer of sharp sand or pea stones should be put into place before the crates are lowered, then the membranes should be fitted inside the hole, ready for the  crates to sit on top of.

Some crates have a separate section in place for the stormwater drainage pipe to be connected. If not, the drainage pipe can be placed next to the crates and held in place by the side fill.

To secure the crates, remember to add side and back-fill to the crates. This can be done using sand or pea shingle, which needs at least six inches to be placed around the sides and on the top of your crates.

The last step is to replace any ground and turf that was removed or any other relevant surface topping.

At KJC Drainage we are experts at fitting rainwater soakaways. Contact us today to enquire about soakaway installation options.

How do I know if I have a rainwater soakaway?

The easiest way to tell if you have a rainwater soakaway is to check for a soakaway pipe near any septic tanks.

You should also see pipes running from the roof to a shallow area in the ground, which is almost an immediate identifier of an already installed soakaway.

How deep does a rainwater soakaway need to be?

Depth is important, but it is also important to ensure the drainage fields are permissible based on the soil.

A percolation test is done to check the porosity of the soil. If the water soaks away either too fast or too slowly, then a soakaway drainage field is not permitted based on the results of the percolation test.

Otherwise, the maximum length of a single trench is 30 meters. Soakaway drain field trenches should be filled to a level of 50mm above the pipe and covered with a layer of geotextile membrane to prevent silt entry.

Choose KJC Drainage for your rainwater soakaway solutions

Are you experiencing problems with surface water drainage or trying to determine if your property has the correct provisions to install a soak away? KJC Drainage is fully-equipped to assist with any matters related to surface water drainage and soakaway installation.

We are a drainage company with over 20 years of drainage service experience. We can assess your property to determine where the best place to install a soakaway on your property would be and can also assess and address all matters related to sewage treatment and a blocked soakaway.

If you are interested to know more about soakaway installation contact us today.

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