How to improve inadequate backyard drainage?

[Simmosp1]

Hi  Bunnings Workshop Community!

This is a great knowledge resource.

I'm starting to embark on a project on my back yard to replace a failed retaining wall and add drainage to the ground in front of the wall.

The house is about 35ish years old and is cut into a sloping block, front(low) to back(high). So we have a flat area  immediately behind the house about 20-25m x 4m then the retaining wall(20-25m long).

There was no drainage behind the redgum retaining wall (hence the  failure), which I expect to be a similar age as the house. I will be replacing it with concrete sleepers and drainage! 

My question though is regarding drainage of the flat ground area. There is an old French drain 65mm slotted coil about 1 metre in front of the retaining wall that spans the entire 20+ metre length, and is connected directly to stormwater pipe - not via a pit.  It does not do a very good job of draining the water after heavy or sustained rain. The drain coil does not appear to have any sock, it has scoria rock around it and has some sort of loose shade cloth around it also.

I was thinking about adding another drain parallel about 2 m away and connect the 2 drains at regular intervals, but in addition to that I'm now thinking that maybe I need to dig out the old drain and renew it?

If digging it out and renewing it is the way to go then perhaps doing it properly with a 100mm slotted, socked drain coil and 300mm wide trench would be adequate on its own and not need any additional parallel drains?

Is 1 pit where the storm water is connected enough for a 20m drain?

Thanks 

Simon

[EricL]

Hello @Simmosp1, 

Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about your drainage.

Is the Vinidex 100mm x 20m Socked Slotted Draincoil enough to drain away all the rainwater falling in front of your retaining wall? There are many factors to this question. Do you have thunderstorms that last more than a day? Are there other sources of water falling into this section? Do you often find a large puddle of water forming a small pond in that section? If those are the conditions in your area, then an additional channel will be necessary to drain away the water flowing in.  

I don't recommend connecting the new drain to your old one. I suggest removing the old 65mm coil and putting in two new 100mm drains in parallel. This will guarantee that the French drain will have sufficient capacity to take on a large volume of water.

Another option is to use Everhard 3m EasyDRAIN Polymer Grate And Prejoined Channel. 

Just a friendly reminder that connecting to your storm water drain will require the services of a plumber for safety and compliance. 

If you have any other questions we can help with, please let us know.

Eric