How Deep Should a Soakaway Be Dug?

A soakaway is a hole in the ground that collects and stores water. It is usually filled with rubble, stones or brick debris and is often used in conjunction with a French drain.

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Soakaway Basics

Before you start to dig your soakaway, it’s important to become familiar with some basics. Soakaways are simply pits that are used to collect and store water, which is then slowly absorbed back into the ground. They are most commonly used to deal with excess water from gutters and downpipes, but can also be used for other purposes such as shower or sink waste water.

The size and depth of your soakaway will be determined by a number of factors, including the amount of water that needs to be dealt with, the type of soil you have and the space that you have available. It’s important to get these calculations right so that your soakaway works effectively and doesn’t cause any problems such as flooding.

As a general guide, a soakaway should be dug to a depth of around 1.5m and a width of 3m. However, these dimensions may vary depending on the factors mentioned above. It’s always best to speak to a professional before you start digging, just to be sure that you are doing everything correctly.

Designing a Soakaway

Designing a soakaway is not an exact science as there are a number of factors to consider, including the intensity and frequency of rainfall, the type of soil, the amount of land available and the size of drains connected to the soakaway. However, there are some basic guidelines that can be followed to ensure that your soakaway is effective.

The first step is to calculate the volume of water that will need to be soaked away. This is dependent on a number of factors, including the intensity and frequency of rainfall, the type of soil, the amount of land available and the size of drains connected to the soakaway. Once you have an estimate of the volume of water that will need to be soaked away, you can then calculate the size of soakaway required.

The depth of a soakaway is also important in its effectiveness. The deeper the soakaway, the more effective it will be in soaking up water. The recommended minimum depth for a soakaway is 1 meter (3 feet), but it can be deeper if necessary.

Once you have designed your soakaway, it is important to test it before use. This can be done by filling it with water and then monitoring how quickly the water disappears. If necessary, adjustment to the design can be made before putting it into use.

Why Depth Matters

When you’re planning to install a soakaway, one of the first things you need to decide is how deep to dig it. The depth of your soakaway will determine how much water it can store and how quickly it will drain away.

Rainwater soakaways are most effective when they are located at least 1.5m below the ground. This allows them to take advantage of the natural underground water table, which stores water in pores and voids in the soil.

Soakaways dug any shallower than this may still work, but they may not be as effective during periods of heavy rain. They may also be more likely to cause problems for your property, such as flooding or waterlogging.

How to Calculate Volume

To calculate the volume of a rectangular shape, multiply the length by the width by the depth. You can also use our cubic meter calculator to find the volume of a rectangular or cube-shaped garden soakaway.

Building Your Soakaway

A soakaway is a very effective way of dealing with stormwater runoff from your property, and can be built relatively easily and cheaply. However, there are a few things to bear in mind when planning and constructing your soakaway, such as the depth that it needs to be dug.

As a general rule of thumb, your soakaway should be dug to a depth of at least 1.5m (5ft), and preferably 2m (6.5ft) if possible. This will ensure that it can effectively deal with the amount of water that is likely to run off your property during a storm.

It is also worth bearing in mind that the size of your soakaway will need to be proportional to the size of your property; a small soakaway is not going to be effective on a large property, and vice versa. As such, it is important to get the size and depth of your soakaway right from the start, in order to avoid any problems further down the line.

Maintenance and Upkeep

Most people are unaware that soakaways need to be maintained and cleared of debris on a regular basis, much like gutters and drains. A build-up of leaves, twigs, and other organic matter can clog the pipe leading from the soakaway, causing flooding. Regular maintenance will also ensure that the soakaway is functioning properly and doesn’t become a breeding ground for mosquitoes.

Soakaways should be cleaned out at least once a year, and more often if they are located in an area with a lot of trees or other vegetation. The best time to do this is in late fall or early winter, before the rainy season begins.

To clean a soakaway, you will need to dig it out. The depth of the hole will depend on the size of the pipe leading from the soakaway. A general rule of thumb is to dig the hole twice as deep as the pipe’s diameter. For example, if the pipe is four inches in diameter, you should dig the hole eight inches deep.


Q: How deep should a soakaway be dug?
A: The minimum depth of a soakaway should be 1.5m below ground level; however, this may need to be deeper in some cases (e.g. if the water table is high).

Soakaway Case Studies

See our Soakaway Case Studies for examples of the types and sizes of soakaways we have installed for our customers.

Soakaway Design Tools

There are many factors to consider when designing a soakaway, including the size of the area to be drained, the type of soil, the amount of rainfall, and the anticipated level of use. Depending on these factors, the depth of your soakaway may need to be anything from 0.6m to 3.0m.

There are various online tools available to help you calculate the required depth for your soakaway, such as this one from the National Soil Resources Institute.

When you have calculated the required depth, you will need to dig a hole that is at least 1.2m deep and 3.0m wide in order to accommodate the soakaway components. Once you have dug the hole, you can then start to assemble your soakaway.

More Information

A soakaway is a pit or underground chamber that is used to collect and store rainwater. The water is then allowed to seep away naturally, rather than overflowing into drains or watercourses. Soakaways are usually dug to a depth of around 2m, but the depth will depend on the soil type and how much water needs to be drained away.

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