Close up image of drainage gutter | featured image for drainage gravels.


Drainge Gravel

Drainage gravels are generally used to facilitate the movement of water around your property or more to the point, away from it altogether! The most common usage is behind retaining walls or sub-surface drainage trenches running underneath lawns and gardens. Drainage gravel is essentially used in any location where you need water to run freely and with minimal resistance.

Every landscape project is different and may require different quantities and sizes of drainage material. Centenary Landscaping Supplies can supply drainage gravel material from a shovel to a truckload and have it delivered to your project.

The sizes available are 5mm, 10mm, 20mm and 40-50mm. Larger sized rock is also on hand or can be sourced.

Larger rock with its irregular nature has larger air spaces or voids when packed into a drainage system. This tends to lead to less restriction and greater water flow capacity. Unfortunately, as the size increases, it becomes harder to shovel! The most common sizes used are 10mm and 20mm. The 20mm variety is perfect for retaining projects and most French style drainage systems.

Both varieties of gravel, those manufactured from crushed rock and those from recycled crushed concrete are available and stocked in our yard at Darra. Both options are just as effective, with some weight and price benefits seen in the recycled products. If you need help in calculating the amount you need, just give the sales team a call on 07 3373 4999 or head to our online store to book your delivery.

How important is drainage and drainage gravel?

The short and simple answer is, EXTREMELY!

When building a wall, be it retaining a stable “cut” in the land or holding back a large surcharge of fill, the effort we put into the drainage behind the wall is crucial to the success of the wall itself. By erecting a vertical or near vertical structure at a point where the land changes in height, there is the potential for it to become a “Dam Wall”. If this occurs, water will be trapped behind the wall where it could build up the pressure and in some cases result in the wall failing and falling over.

In any DIY video or guide produced, there will always be a strong emphasis on the drainage material used behind the wall being built. The main function of a well-designed drainage system is to ensure rainwater can escape away during heavy or extended wet periods. This is done by placing an Ag Pipe at the base of the wall (behind it) and then covering this with drainage gravel. The quantity of drainage gravel used will vary depending on the height of the wall and the amount of water runoff expected but as a general rule, the more gravel used the better. Refer to the diagram of a typical retaining wall drainage system presented here.

One thing to avoid at all costs is lining the back of the retaining wall with plastic as this will indeed result in water being held behind the wall. If you are concerned about dirt seeping through the joints in the wall, then you can line the wall with a filter cloth called Geofabric (Bidim) as this will let the clean water drain through and hold back the dirt.

When designing your wall, check the manufacturers’ brochures or the DIY videos and guides on our website to get the full story on the importance of drainage, drainage gravels, and how to design an adequate drainage system.


Ready to buy? Head on over to our online store and get your next Landscaping Project underway.




Expert advice for a great home & garden!