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My yard is flooding!

It has floway pit that connects directly to a 90deg PVC bend, then that connects to the storm water pipe via another 90deg bend. So there are two 90 deg bends in the span of 500mm. There is no rainwater pit beneath this. The storm water pipe is properly graded at 2.6% decline.

When there's moderate rain, the yard floods and the drain is submerged. Looking for suggestions to resolve this.

Would using a rainwater pit resolve this? Is the fact there are two 90 deg bends in a short distance causing a bottle neck?

Existing drain. Floway. enter image description here enter image description here

After moderate rain. Drain is submerged. enter image description here

Existing drain's connection to storm water pipe. Two 90 deg bends. enter image description here

Should I remove the floway and install a rain water pit and connect that to the storm water pipe instead?

enter image description here

Update: Full context. Pink = storm water pipe (my best guess). enter image description here

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  • There's a Tee - Where else does that storm drain line connect to?
    – Ecnerwal
    May 16 at 12:00
  • See update with birds eye view of the property. The overflowing drain is the one in the back yard. Pink = storm water pipe. May 17 at 2:44

2 Answers 2

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You can always dig up and replace plumbing, install catch basins, etc. if you want to spend money, but if this was your bathroom sink drain that was clogging up instead of the yard drain, the first thing you'd do would be to work on clearing the clog from the bathroom drain, not replacing all the plumbing. I'd strongly recommend that you work on doing the same for your yard drain.

While the drain head has the little grid on it to help keep things from getting into the drain plumbing, stuff will fall through those slits - small leaves or twigs, bugs, little critters looking for nesting places, etc. Pull the cover and run an augur down the drain to see what you get.

You'll likely have some difficulty getting the augur around those tight 90° elbows, just like all the yard detritus is having a hard time getting around them, and that's likely where your backups are.

If you can get it augured out and get it to flow freely (run your garden hose down the drain to confirm that it's no longer backing up, instead of waiting for the next rain storm), you might consider digging up and replacing the 90° elbows with 90° sweeps to make it easier for water and other little things to flow around the bends instead of around corners.

A simpler fix than replacing elbows would be to put some hardware cloth (like heavy-duty screen door screen) under the drain cover. Cut a piece to fit across the top of the pipe then put the hardware cloth on the pipe and screw the drain cover on top of the cloth. The hardware cloth has very small holes that will keep all but the smallest bugs out, and, when it gets clogged up, you will, most likely, be able to clean it by pulling the twigs and leaves back up through the drain cover instead of having to run an augur down the pipe. Eventually, you'll probably have to unscrew the drain cover, pull out the somewhat damaged hardware cloth, and replace it with another $1 piece.

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  • Using the pit drain instead gives debris a place to collect that isn't down the pipe - if you clean it out occasionally (otherwise it just collects until it's running into the pipe again...seen that plenty of times.
    – Ecnerwal
    May 16 at 11:59
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    Might add one thing: if the total volume of water per unit time falling on this ground area exceeds the flow rate of the (presumably not clogged) drain, then you will always get flooding until the rain stops. May 16 at 15:21
  • Excellent point, @CarlWitthoft! It may become necessary to dig it all up and replace it with larger pipe to handle greater rain fall.
    – FreeMan
    May 16 at 15:22
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    @FreeMan or a second pipe working in parallel to the first with it's opening in a different part of the flood zone. May 16 at 19:49
  • Thanks for the helpful replies. I added a birds eye of the property showing the storm water pipe, down pipes and drains. The dashed pink link at the back of the property is the council storm water line. I suspect the downpipe in the back yard, just after this overflowing drain might be causing significant backpressure, causing the flooding. May 17 at 2:42
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This much standing water tells me that you need perforated drainage tile* or pipe* in addition to your drain(s).

This will pull water from the ground after it's soaked in as well as removing surface water. Simply having a storage tank for water doesn't look like it'll make enough of a difference for you. The drain you have is designed for quick removal of water, which you definitely need, but adding the perforated pipe will help remove the water that doesn't directly lead to the drain.

You will need to put tile under all the lawn that is flooded, so you might have to tear up more of the grass than just replacing the current system.

A well designed garden landscape can transform your outdoor space, but it is important to protect your garden from changing weather conditions. Using perforated pipes discreetly in your garden landscape can help to absorb excessive rainwater, draining it away from your garden and property. By installing perforated pipes under the ground, excess water can be drained away so that your garden landscape is not at risk of damage.

https://www.coastaldrains.co.uk/blog/the-perforated-drain-pipe-and-what-you-need-to-know/

Replacing each of the 90 degree corners with 2x 45 degree elbows will help the flow and let you remove blockages easier, but it's not the whole problem with your flooding. You just don't have enough points of entry to the drainage system, which is the real problem. Adding more drain grates won't hep much, since you also need to deal with the water soaking into the ground. And adding more grates won't help much if your current pipe is already at full capacity which is likely why the grate is submerged.

(Looking at your 90 elbows again, you can probably only replace 1 with the a single 45 and turn the drain accordingly. Or if it's actually a T, replace it with a Y*.)

Simply putting in larger drain grate won't solve the problem of not having a pipe capable of handling the extra flow. Since your current drainage can't keep up with the rain, causing the drain to be submerged, it sounds like you need to increase the diameter of your pipe anyway. You mention that even a moderate amount of rain causes the drain to be submerged, so I'd suggesting looking to increase the pipe by at least 1.5-2x what you already have.

And, for a complete answer, I'd definitely suggest trying to unclog your current system first, like FreeMan says. This kind of hinges on whether the drainage system ever worked well to begin with. If it could never handle this amount of water, you will need to increase the size of your pipe. And since you have standing water after the drain catches up, you still need need perforated drainage tile/pipe to let your lawn dry out.

*These are examples of what to look for, not a store or brand recommendation.

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  • I added a birds eye of the property showing the storm water pipe, down pipes and drains. The dashed pink link at the back of the property is the council storm water line. May 17 at 2:43
  • "And since you have standing water after the drain catches up, you still need need perforated drainage tile/pipe to let your lawn dry out." - I see no evidence of that in the OP's post. If the was standing water and the drain was clear, that would be one thing - but all they show is the drain submerged (so basically "not draining") and standing water. May 17 at 14:38

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