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Need to drain groundwater reemerging from dirt slope under the house

Hi all, I’ve got a dirt slope under the house that has groundwater coming out of it after rainfall, washing dirt and bits of rock down onto the concrete floor of the workshop. There are piers all over the place and the slope is uneven, making it hard to find an obvious path to divert the flow using ah pipe, and I don’t want to go digging because of the piers. Any thoughts or suggestions? Cheers! Jim

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MitchellMc

Hi @jbs1,

You might like to show us some images of the area so our members can get a better idea of what solutions they could suggest. Would you be able to run an Everhard EasyDRAIN Polymer Grate & 3m Prejoined Channel along the edge of the slab to a point where Vinidex 50mm x 10m Black Slotted Draincoil could be connected, diverting the water out of the area? That would only require you to dig a small trench.

Let me mention @Adam_W and @TedBear to see if they would like to join the discussion.

I look forward to hearing more about the situation and providing a solution to your issue.

Mitchell

TedBear

https://www.workshop.bunnings.com.au/discussion/comment/12649#Comment_12649

Hi, my initial thoughts are.... where is this water actually coming from? How long for/is it a relatively new thing?

On the theme of 'Prevention is better than cure' it may be worth trying to see why a stream of ground water is coming toward you.

I had a similar issue in a house many years ago, where a room had been added lower on the block - i.e. it was a step-down room below the house's normal floor level, with a concrete floor. That house was on piers too. After removing smelly carpets after every winter, I eventually found that the driveway crossover at the front of the house (high end of block) wasn't installed correctly and was directing masses of street water into my drive which turned into a shallow stream under my house, came through a crack in the brick wall end of the added room and ended up seeping under my carpets. By the time I smelled it, the stream had always dried up. The council fixed it once informed, and I had no more trouble.

That may not be your situation, but the earlier in the system you can divert that water, the better your result will be.

I am interested to see more on what your own situation is...

redracer01

Hello @jbs1

Welcome to Bunnings Workshop! I am a firm believer of DIY channel drains. I strongly believe in working with nature and not against it. So my solution for you is a two step approach. First I suggest creating a shallow U shaped water drain. It's also know as a spoon drain.

- Prepare your proposed area of the channel by creating a shallow channel about 30mm deep and then flattening it out with available garden tools. Use a level to make sure that the fall of the earth points out towards your nearest garden.

- Once you've prepared the ground you can use Bastion builders mix to prepare a cement channel about 150mm wide and at least 20mm to 30mm thick.

- Use a 2 liter bottle of coke or similar shaped bottle fill with water to prevent crushing the bottle, push down in to the wet cement channel to create the shallow U shape. Finish and feather to desired shape.

- While waiting for your cement to dry, visit your local Bunnings and buy some buffalo turf to cover the bottom area of your slope. It does not need to cover the entire slope just half a meter past the body of your diy spoon drain.

What is the turf for? The buffalo grass serves as a natural water buffer before it hits the spoon drain. The grass traps the water and the debris acting like a natural filter. Buffalo grass is very tough and hardy even in the shade so in essence if the grass survives then it should soak up incidental water. But should you get big rain then the spoon channel will redirect it to the garden. A winner in both situations, please note that in the drawing I've drawn the drain as a curve that is to just illustrate that you can build it with the turn and contour of the earth and does not need to be straight. Just remember that the edge of the drain must be level with the earth otherwise the water will just go past it and under the drain. I hope the drawing makes sense and helps you out.

Cheers,

Red

jbs1

https://www.workshop.bunnings.com.au/discussion/comment/68788#Comment_68788

Thanks, TedBear - your situation certainly sounds pretty challenging, requiring a fair bit of deduction. Mine is a bit more straightforward: the high side of the house had a perfectly-flat pathway of pavers, which sat on a bed of concrete and rock, and for some reason zero drainage. Surface and subsurface water would come down the hill and have nowhere to go but into the pavers and then under the house, onto a base of dirt...just had it ripped up and some drains installed, so hopefully that prevents any further issues! Cheers, Jim

jbs1

https://www.workshop.bunnings.com.au/discussion/comment/12656#Comment_12656

Thanks Red, that's really helpful - if I can't get grass to grow and act as a natural filter, what else would you suggest? Some rock/gravel encased in chickenwire? Cheers, Jim

jbs1

https://www.workshop.bunnings.com.au/discussion/comment/12649#Comment_12649

Thanks, Mitchell - that everhard drain / slotted draincoil sounds like a solid approach: would I need to put a sock over the draincoil, or anything like that? See some pics below. Piers have been recently re-done, and there's now drainage on ground level on the high side of the house, but am anticipating a good deal of subsurface water will still pop out halfway down as it emerges from some rock beds along the slope.

Cheers,

Jim

StevieB

https://www.workshop.bunnings.com.au/discussion/comment/69110#Comment_69110

Hi @jbs1,

Thanks for sharing more about your project.

Let me tag @redracer01 and @MitchellMc so they're alerted to your questions.

Stevie

MitchellMc

Hi @jbs1,

It's great to hear that you installed drainage on the ground level, and I feel this will really alleviate a good portion of the water flow. If you were to install the drain channel across the slope, the drain coil would remove the water from the channel to distribute elsewhere. I seem to have linked to the slotted version of the drain coil, which is not needed as you'll be using it to transfer the water instead of collecting it. Instead, Vinidex 50mm x 20m Black Unslotted Draincoil would be more suitable, and no sock is needed. Alternatively, you could dig a trench 100m wide and 30cm deep around the perimeter of the concrete slab. Drop Vinidex 100mm x 20m Socked Slotted Draincoil into the bottom and backfill with Ki-Carma 20kg 10-20mm Drainage Gravel. The pipe would be run out from under the house and ideally to a stormwater collection pit.

On a side note, this is a very similar situation to under my house except the water can not escape and pools. After the recent torrential rains in Sydney, I had at least 35cm of water sitting there at the bottom of my slope. I'd estimate around 3000 litres that couldn't go anywhere. I'm in a rental, so adding drainage isn't an option for me.

Mitchell

jbs1

https://www.workshop.bunnings.com.au/discussion/comment/13237#Comment_13237

Thanks Mitchell, appreciate the advice; that's an approach I think I'll use over the summer, thanks for the links to the products too. I hope your place dried out ok! Cheers, Jim

jbs1

Hi All, seeking advice on how to drain mainly sub-surface water from a slope of rock and soil over a concrete slab. As you can see in the pictures, I've got a (under the house) workshop floor slab which gets flooded when it rains heavily; water rises up from next to the slab, and also comes down the slope and emerges where the dirt ends and the slab starts. 95% sub-surface, a little surface water if it's deluging.

I'm thinking of a french drain system (gravel, socked slotted ag-pipe) snaking down the slope to gather and direct the water, but am not sure how best to then divert the water over the slab, as I can't direct it either side. Do I build a small retaining wall on top of the slab with a hole for non-slotted ag-pipe to then run outside? Am I going to need a permanent 'sump pump' installed in a basin next to the slab which is fed by the french drain?

Pics attached from looking up the slope and down, showing where I'm planning on putting the french drain and where I've got to get the water out to.Planned french drains above, rectangle shows where water seeps down / rises up onto the slab.From the other direction; where I need to direct the water.

Any thoughts or suggestions gratefully appreciated!

Cheers,

Jim

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/17796#Comment_17796

Hi @jbs1,

I see you've had some work done, but are still dealing with the same drainage issue.

I think you are certainly on the right track. I'd simplify your drainage design slightly and have just one collection point for the whole slope. I believe only one deep French drain constructed correctly will be enough. It can be directed to a stormwater pit that contains a sump pump. The pump can send water out via a 32mm pipe attached to the wall with pipe saddles.

Dig a trench between the slope and the slab to be slightly deeper than the slab. Paint the side of the slab with waterproofer and lay drainage matting on the soil side to stop sediment from entering the system. The matting can be extended up the slope and pegged into it. This should assist with preventing soil erosion from the surface runoff. Personally, I'd be inclined to install a small one sleeper high retaining wall using 0 x 50 x 3mm 0.65m H Joiner Post Galvanised Steel Sleeper Uprights just to future proof the system. Optimally I'd suggest building the retaining wall right next to the slab and having the drainage behind it. Much neater and likely more function that way.

The water will hit the edge of the slab and fall through aggregate into an ag-pipe. The ag-pipe needs to be graded towards the pit.

The only way I can see you doing away with the pit and sump pump is if you cut a trench into the slab with an angle grinder and a diamond blade. In order to establish fall, the trench will need to be quite deep and involve a substantial amount of work.

I've spent some time creating a rendering of my proposed solution for you. I hope it assists you in your project.

There's been some great advice in this discussion already and I'm sure we are all keen to see you solve this issue.

Please let me know if you have any questions.

Mitchell

jbs1

https://www.workshop.bunnings.com.au/discussion/comment/71544#Comment_71544

Thanks Mitchell, that's great - really appreciate you taking the time to put together those images, that's really helpful. Cheers!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/99055#Comment_99055

No problems, @jbs1.

Now that you've made some changes let me mention @TedBear to see if he has any other thoughts.

Mitchell

TedBear

https://www.workshop.bunnings.com.au/discussion/comment/116323#Comment_116323

Thanks for the tag @MitchellMc . I am very impressed with your design and images... I can't think of anything to add to that!

Ben2065

https://www.workshop.bunnings.com.au/discussion/comment/12656#Comment_12656

Hi @redracer01 ,

I loved your diy concrete spoon drain concept and instructions. Can I ask for my own project I am considering a 13m long run spoon drain down my soil laneway (slightly curved in its path). Is it best to install expansion joints or unnecessary? Also is there any need for mesh in the concrete as it will only be foot traffic and garbage bins (no vehicles). I understand you are suggesting the soil trench be about 3cm thick and 15cm wide? I will also be installing buffalo turf either side of the drain to assist with water slowing, sediment collection and water absorption. I really haven't seen a spoon drain construction so clearly and simply explained, Thank you!

EricL

https://www.workshop.bunnings.com.au/discussion/comment/80590#Comment_80590

Hello @Ben2065

I suggest building it in 1-meter lengths and joining the drains with silicone. In this manner it will have a measure of flexibility in case there is any ground movement. Putting in mesh into the assembly is always a plus and will give the drain extra strength.

The measurements you've mentioned are recommendations and if you feel that you need a larger spoon drain you can adjust it to your needs. The beauty of a D.I.Y. spoon drain is that you can adjust its size and put in modifications which you feel will improve its overall function.

For example, you can build a round soil catcher in the run. It's basically a round concave cement dish that traps the soil in the middle but still allows the water to flow away.

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

Eric

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