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

[donmattdon]

Hi, wondering where the end of the pipe goes. One end will go into the drain/basin for the water to drain into but what do I do with the other end?

[MitchellMc]

Welcome to the Bunnings Workshop community @donmattdon. It's a pleasure to have you join us and many thanks for your question on drainage pipe.

On the uphill side, the pipe typically doesn’t connect to anything, as it serves as the start of the drainage run and is usually capped off. From there, the pipe is set on a slight slope, allowing it to collect water and direct it towards a stormwater pit or stormwater pipe.

Please let me know if you have any questions.

Mitchell

[donmattdon]

Thanks Mitchell! Follow up question. I have an existing drain with has a black plastic catch basin. I assume I need to drill into this on the side so I can run the pipe into it. Do you have any advice on how to drill a hole in the side? Or would it be better to replace the basin with one that already has a hole in the side?

[MitchellMc]

Hi @donmattdon,

Drainage pits don't typically come with a hole in the side and this is something you need to drill yourself. If there is already one in the ground, it would likely be easiest to dig your trench up to the side of it and then drill the hole to accept the pipe. You might need to clear the soil in that area to get the drill in, but the trench should give you enough room.

Once you've got the trench in place, drop the drill sideways in the hole and drill into the pit with a holesaw bit.

Mitchell

[donmattdon]

Hi @MitchellMc ,

Thanks for the tips. I have an area that is just dirt now and looking to put drainage in and then lay turf. Should I just cover the drainage channels with sand and the rest of the area with soil before putting the turf down or can I just use soil over everything?

Also, if I am using a socked pipe, is it still recommended I use fabric?

Thanks!

[JacobZ]

Hi @donmattdon,

Assuming you use drainage gravel and geotextile fabric around the pipe, then putting soil over the top is perfectly fine. The sand @Adam_W has used above is more to level out the turf than anything practical related to the drainage.

Even if you use the socked agi-pipe you should still use geotextile fabric as it will stop the soil from eroding and settling between the drainage gravel. Drainage channels like this work by creating a path of least resistance through the soil. If the channels through the drainage gravel are blocked, then the water will not find it as easy to get to the agi-pipe, meaning it could find another path of least resistance elsewhere.

It's best to use the geotextile fabric as it will keep the drainage working for as long as possible.

Let me know if you have any further questions.

Jacob

[donmattdon]

Thanks @JacobZ!

I have been digging my trenches for the pipes. With the fabric, I plan on putting it on the bottom of the trench, gravel on top, pipe, more gravel, then wrap with the fabric. Is this ok?

Also, if there are spaces around the fabric after it’s all wrapped up, would I be ok to fill it in with the existing dirt that I dug up? Can I also lay that dirt on top effectively burying the piping? And then lay the soil over the sop of everything?

Thanks again

[JacobZ]

No worries @donmattdon.

Short answer, yes, yes, yes and yes.

Everything you've said is perfectly fine and will close out your project well. Just make sure you compact the gravel when it goes in the trench and then compact the soil when you backfill around everything.

Let me know how you go and if you have any other questions, please don't hesitate to reach out.

Jacob

[Gibbster]

Hi following this one - just had new concrete laid and thought was to run this type of drain around the perimeter to stormwater pit. The thought I was to stop the water seeping under concrete once the trench dug first a layer of sand then lay black plastic and attach the black plastic to the concrete edge using adhesive backed expansion joint foam then gravel the drainage mat then sand then turf - thoughts? Not sure if the water Sitting in the trench may cause the concrete to drop over time?

[JacobZ]

Hi @Gibbster,

A warm welcome to the Bunnings Workshop community and thank you for your question.

It's an interesting idea, however, I'm not certain whether it would be worthwhile. 

French drains create a path of least resistance through the earth that will capture any groundwater above where they sit. They capture the water that flows into them and carry it away through the agi-pipe, but they also allow water to drain naturally into the earth beneath. They are more about reducing the level of groundwater than they are about taking everything away.

My thinking is that adding an impermeable barrier beneath the drain limits the water's ability to drain down into the soil naturally which I don't think is worthwhile.

Realistically, I don't think what you're proposing will have any negative effects, but I don't think it's necessary.

Allow me to tag @Nailbag, @DirtMonkey and @Dave-1 for their thoughts.

Let me know if you have any further questions.

Jacob 

[Dave-1]

Afernoon @Gibbster 

I dont really see a benifit to putting even an ag pipe in. Your concrete slab should be fine on its own. If you notice run off in the future then an ag-pipe could be a solution to deal with it. But as something to deal with sub-surface water movement I dont think it owuld tip teh scales in helping the concrete.

Socked ag pipes I would only have fine gravel underneath, rest pipe on that gravel and then cover with gravel until say 20mm above the socked ag pipe. then cover with soil. I have installed my stormwater PVC pipes the same way and as I have high content of clay the channels also carry water Water will always find a way to seep using the easiest path. I definently would not try to use any plastic around the area you are planning on using the ag pipe.

Dave

[donmattdon]

Hi @MitchellMc and @JacobZ,

Thanks again for the advice. The project is finished so I thought I’d send through some photos!

Matt

 

   

  

  

  

 

 

   

[Gibbster]

Thanks JacobZ Dave-1 just adding a pic - I have a low point in the corner - the drain pit is in the centre of the grass at the back two meters to the left and two meters to the right I will be able to get the water to run with the slope of the land will soil and turf it’s real just that corner - there is another drain pit to right at the end of the concrete pathway - thoughts? 

 

[Dave-1]

Afternoon @donmattdon 

Thats a nice looking area Would love to see a couple of pics later on especially after a downpour I like your amount of effort you have gone to!

Dave

[Dave-1]

Afternoon @Gibbster 

I dont see a problem with what you are describing. I would just steer clear of lining the edge of the concrete or trenches with that black plastic you mentioned. I would probarly have a bit of a poke at that bare patch and see what the soil compesition is like. Mainly because its bare and looks compacted. When I first moved into both houses I have live din there always seesm to be a dead patch of lawn next to the garage/driveway where I suspect the pervious people have "emptied" out stuff that they really shouldnt have, both pathes took aver a year and a half to recover.

I would also check the PH of the soil in that area. 

Dave

[JacobZ]

Hi @Gibbster,

@Dave-1 has already said much of what I am thinking but I do have a question for you.

Are you finding that water pools against the concrete, so you are struggling to establish grass? Is this why you've thought about putting black plastic to protect it?

If so, adding material to raise what appears to be a low spot against the concrete so the surface water doesn't pool against the concrete seems like a good way to go. I still don't think the black plastic will really be beneficial, but adding a french drain is still worth while.

Let me know what you think.

Jacob

[JacobZ]

Hi @donmattdon,

Brilliant work mate, that looks like a fantastic drainage solution for the space.

Has the lawn just gone down?

I'd be interested to see how good it looks once the roots have established and you can get a mow in.

Merry Christmas and thank you for sharing.

Jacob