Drainage Pits, Channels & Pipe behind wall

In any landscape project, the drainage of an area is critical to the overall success of the job. Not only is it important to include drainage material behind retaining wall, it is also critical to incorporate adequate drainage systems throughout your entire project to prevent possible issues and flooding.

If you need advice on your drainage options see our DIY videos and DIY Guides, or speak to the sales team on 07 3373 4999.

How important is drainage? How important are drainage pits, channels and pipes?

The short 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 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 rain water 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.

Installing Drainage Systems in paved areas

Check out this simple DIY video on how to install surface drainage systems.