Yard floods - will replacing a floway drain with a rainwater drain resolve this

Question

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.

After moderate rain. Drain is submerged.

Existing drain's connection to storm water pipe. Two 90 deg bends.

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

Update: Full context. Pink = storm water pipe (my best guess).

Answer 1

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.

Answer 2

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.