How to install garden drainage

[Adam_W]

Difficulty: Beginner

Often the best way to fix a muddy lawn is by installing underground (sub-surface) drainage.

Here’s how to install a concealed drain to prevent water pooling and help keep your lawn lush and healthy.

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Steps

Step 1

Decide where to put your drain, and then dig your trench. The rule of thumb is that your pipe should have a space equal to its own width on either side, and at least 100mm from its top to the finished level before the turf is replaced. In our case, the trench is about 200mm wide (65mm space + 65mm pipe + 65mm space) and 180mm deep. Use your level to ensure that the trench is falling slightly in the required direction.

Step 2

Lay your pipe in the trench, ensuring it is sitting on the trench bottom. Use your level to check that the fall is correct. Cover with gravel to about 20mm below the existing surrounding soil level. The pipe must be run to a suitable point for dispersal (we connected it to an existing sub-surface drain).

Step 3

Trim your drainage fabric to suit the width of your trench. Place it on top of the gravel.

Now, fill the remaining 20mm of your trench with coarse sand.

  

Step 4

You can now lay your turf on top of the sand. Use your spade to trim the turf. Use excess sand or loose soil from your excavation to fill gaps along the edges and ends.

Walk lightly over the area to ensure that turf is in contact with the sand base, then water well. The first thing you’ll notice is that the water disappears.

Step 5

To finish, replace surrounding turf so that your new turf blends seamlessly. Remove a little soil and replace with sand to improve drainage of the whole area.

Keep your turf moist but not wet while it establishes and apply a seaweed tonic every week for the first few weeks to help it establish. As moisture retention will be low above your drainage trench it may need extra watering during dry periods.

Materials

• Slotted agricultural drainage pipe, socked (we used 65mm diameter pipe)

• Non-slotted agricultural drainage pipe of same diameter (for moving collected water to the dispersal or disposal point)

• Drainage fabric

• Drainage gravel (we used two bags)

• Coarse sand (we used one bag)

• Rolls or slabs of turf to suit.

Tools

• Digging spade (a trenching shovel is handy but not essential)

• Short to medium-length level

• Utility knife or heavy-duty scissors

• Wheelbarrow.

Images

[nick626]

Step 3 instructions are missing. Can you tell me what you used to cover the gravel please 

[MitchellMc]

Great pickup, @nick626! The remaining height of 20mm is filled with coarse sand. The sand should then sit level with your surrounding soil.

We'll fix that step up.

Thanks!

Mitchell

[TimTDP]

I would like to have seen how the slotted pipe is terminated at each end, especially at the lower end. It would be good to know what fittings are required.

I am intending to drain it to a drainage pit and from there to the storm water system, preferably via a 50mm PVC pipe (since the flow is small and the route is tricky) if I can adapt that pipe to a 90mm storm water pipe. 

[MitchellMc]

Welcome to the Bunnings Workshop community @TimTDP. It's terrific to have you join us, and many thanks for your question about connecting agipipe.

You'll use a Everhard EasyDRAIN Pit Boss Connector to connect your slotted agiline to the drainage pit. A hole is cut in the side of the pit, and the connector is screwed to it with silicone used to seal the fitting to the pit.

For the pits outlet, you could attach a 50mm pipe, but as that's not a common usage, you'll need your own fittings. You could cut a 50mm hole in the pit and insert a Holman 50mm PVC DWV Male Threaded Iron Adaptor. On the other side, screw on a Holman 50mm DWV PVC Female Iron Adaptor. You'll then have a 50mm push-in connector in the pit's wall to attach your 50mm pipe.

To jump the 50mm back up to 90mm, you'd likely need a Holman 90 x 75 x 65 x 50 x 40mm Storm PVC Stepped Adaptor.

Remember that a plumber is required to make any drainage connections to your mains.

Please let me know if you have any questions.

Mitchell
 

[TimTDP]

Thanks for all those tips @MitchellMc, very helpful. I like the idea of using the two threaded adapters, I was thinking of using two 50mm Flanges  bolted together sandwiching the pit wall with a seal but the threaded connectors are probably easier.

I have since found another 90/50mm adapter I can use,  Holman 90 x 50mm Round PVC Storm Downpipe Reducer which I think will work and is a little more compact.

Cheers,

Tim.

PS I am not connecting to any mains. This whole project concerns only drainage within my property,

[nick626]

Garden drainage

Can I ask how a drain pit works and is it a good idea to install one or is it optional and if one isn’t installed where do you direct the water to. 

[MitchellMc]

Hi @nick626,

Drainage pits are essential for managing water flow in long runs of grating or collection pipes. They are installed at intervals to prevent overloading the system with large volumes of rainwater. Connected to collection pipes that feed into the stormwater line, these pits ensure efficient drainage and prevent water from traveling the entire length in one go. For short lengths of collection, they are not necessary.

Unlike soakwells, drainage pits are purely collection points. Water enters through an input and is then directed out through an output to the stormwater pipes. A soakwell, on the other hand, collects water and allows it to gradually seep into the surrounding soil.

Please let me know if you have any questions.

Mitchell