Pool Over-Drains After Heavy Rain

[wjmano]

This is a total mystery to me because I don’t know how this can happen with what seems like a very simple drainage system.

I have a vertically orientated PVC pipe within an enclosed cutout in my deck which my pool water runs into from a bottom access hole. When my water level gets higher than this PVC pipe, the water simply runs down the tube and drains into my yard. Simple enough. My water level can stay stable right near the top of this tube for days. But if I get a heavy enough rain one night, I’ll wake up and the pool has over-drained to the point where the water is 2 inches below the top of the PVC pipe. This usually occurs to such an extent that my auto-fill turns on to add fresh water.

My question…how can the water possibly drain beyond the top of the PVC pipe? Since a moderate rain can allow my water level to increase to the very top of the drain pipe and remain stable for days, I dont have a leak. It’s only when I get enough rain to force the water level over the tube with a heavy rain does it then over-drain and drop too low.

My short explanation here is probably not enough for an obvious answer, but thought I’d throw this out there in case someone has had a similar issue.

The only thing I can think of, is it has something to do with the plumbing where my drain tube is located, so I’ve included a picture from above. The access hole where the drainage pipe is located is somehow plumbed into my nearby skimmer hole with the intent to naturally maintain similar water levels - I assume.

Thanks in advance for any thoughts or advice.
Bill

 

[Newdude]

My stab at it is the wind. If the prevailing winds in the storm are pushing water towards the skimmer/drain, it would fill and splash out over and over and might be noticeable given a long enough storm.

 

[rcerf]

If you figure it out, let me know. Mine does the same thing in a very heavy rainstorm. I have the same autofill drain setup as yours, the only difference is my drains to daylight.

 

[wjmano]

If you figure it out, let me know. Mine does the same thing in a very heavy rainstorm. I have the same autofill drain setup as yours, the only difference is my drains to daylight.

What do you mean when you say it drains to daylight?

 

[wjmano]

My stab at it is the wind. If the prevailing winds in the storm are pushing water towards the skimmer/drain, it would fill and splash out over and over and might be noticeable given a long enough storm.

Thanks for the thought. If it didn't do this consistently I might agree this could be a possibility. I'm also inside of a birdcage, so the impact of any wind is quite diminished.

 

[Newdude]

I'm also inside of a birdcage, so the impact of any wind is quite diminished.

Gotcha. That’ll make a huge difference then. Lol. Hang tight for more thoughts

 

[rcerf]

It just means the drain line terminates out to an area away from the pool.

 

[phonedave]

What do you mean when you say it drains to daylight?

When a drain is daylighted it means it terminates above ground. The end of the drain pipe comes out of an embankment, and the drained water turns to surface runoff. As opposed to being plumbed into a stormwater system (which is more and more often becoming illegal) or into a dry well or other impoundment.

You say in your original post "a heavy enough rain". What is heavy enough. Are you talking about a sudden downpour? Does it happen with a steady light right over a long period of time?

Thanks

 

[wjmano]

When a drain is daylighted it means it terminates above ground. The end of the drain pipe comes out of an embankment, and the drained water turns to surface runoff. As opposed to being plumbed into a stormwater system (which is more and more often becoming illegal) or into a dry well or other impoundment.

You say in your original post "a heavy enough rain". What is heavy enough. Are you talking about a sudden downpour? Does it happen with a steady light right over a long period of time?

Thanks

It doesn't have to be a sudden downpour but it does need to be a solid amount of rain over time.

Since the pool is relatively new to us, I'm still learning and piecing things together. It took me (and my pool builder) quite some time to rule out a leak somewhere. Now I'm starting to develop a different cause and effect. The other piece of the puzzle may have something to do with having the pump off, since my issue seems to occur overnight when the pump is off.

I just may have to wait for the next heavy rain and camp out overnight to simply watch the water drain. Sounds like fun!

Thanks!

 

[Bill1974]

Does the cover have a hole in it like a skimmer cover? If not I am assuming when there is a heavy enough rain that is completely fills the drain pipe it turns into a gravity syphon. This syphoning continues till the seal between the cover and the box dries out enough to break the vacuum.

Simple test would be to leave the cover off when it's rains and see of it happens still. If that stops it, just drill a couple of 1/4" holes in it.

If it continues to happen I am at a loss.

 

[wjmano]

Does the cover have a hole in it like a skimmer cover? If not I am assuming when there is a heavy enough rain that is completely fills the drain pipe it turns into a gravity syphon. This syphoning continues till the seal between the cover and the box dries out enough to break the vacuum.

Simple test would be to leave the cover off when it's rains and see of it happens still. If that stops it, just drill a couple of 1/4" holes in it.

If it continues to happen I am at a loss.

Interesting idea! No hole in the cover and it seals pretty well.

My first thought was a siphoning effect, but I logically figured once the water level got below the riser pipe it broke the vacuum. Something may be causing the water level in my overflow cylinder to exceed the pool's water level. The sealed cover may be the culprit. I will definitely try leaving the cover off next time.

Thanks

 

[Newdude]

Something may be causing the water level in my overflow cylinder to exceed the pool's water level. The sealed cover may be the culprit. I will definitely try leaving the cover off next time.

What about the rain water puddle on top of the cover pushing down on the pool water and forcing it out the overflow ? Many above grounds have that exact issue over winter when closed with a tarp. After a certain amount of top water, every new drop pushes out bottom water.

 

[Bill1974]

I am guessing the housing you have the overflow in is sealed decently once it rains and fed from the bottom of the skimmer. Other options to cause a tidal shift or storm surge on one end you pool are pretty remote, I think we would see bigger natural disasters if this was the case.

Having an overflow is a nice idea. I am sure the 4 or 5 times my pool has over flowed this year is not great for it. Not sure an overflow drain would have prevented it (not sure what size drain I would need for a 4 inch/hr or more downpour), but at least it would have limited how long it stayed that way. I wish put them in when I replaced my skimmers earlier this year. I'm have the patio around the pool done soon so I will have the change to put one in. I have heard that some have used the port on the back of the Hayward skimmers for this purpose.

 

[Newdude]

I wish put them in when I replaced my skimmers earlier this year

I seriously considered it for my build soon but we don’t have them here for a reason. You would have to plug the pipe with a rubber stopper for winter and when the block of ice shifted it would pull it. The refreeze would likely blow the pipe and undermine the patio.

The best I could come up with was to use foam rope down the pipe to absorb any freezing, which would be great until that got forced further down / stuck / caused a blockage.

Then wherever it drained would likely have a puddle, possibly from the yard itself and not the pool, which would also freeze and take out the last few feet of pipe every other year.

Whattayagonna do ?

 

[Rich D]

You would have to plug the pipe with a rubber stopper for winter

I don't have an overflow either but I sure wish I did. I am not following your logic of why it would freeze? The water gets drained down below the inlet from the pool to the skimmer where the weer door is and you're overflow should be well above that level and I believe the whole idea is to keep the ice and water below the tile and the skimmer correct? The guys that close my pool put a emty 1 gallon jug in the skimmer and jam a whole bunch of rigid foam all the way around to almost take up the entire inside of the skimmer. I really could not see the possibility of that line freezing.

 

[Bill1974]

I did not even think of the winterizing aspect of it. But plugging them would be pretty easy. And I think my water level never gets that high over the winter either. I've dealt with light niche leaks that have me more worried about to little water in the pool. I think I solved that issue with a new light niche. I had the wimpy brazed on conduit nut cut off and had a proper stainless steel conduit coupling TIG welded on. So it's not going anywhere now.

 

[Newdude]

The guys that close my pool put a emty 1 gallon jug in the skimmer and jam a whole bunch of rigid foam all the way around to almost take up the entire inside of the skimmer. I really could not see the possibility of that line freezing.

The skimmer itself would be 90%(?) other material. But it would only take enough water to fill and freeze in the 3/4 inch pipe. I had a mesh cover and the water level returned pretty quickly. So one would need frequent drains to remain plenty low. 3 inches can happen in a week on a wet week.

I believe the whole idea is to keep the ice and water below the tile and the skimmer correct

Correct. But once it freezes you can’t touch it until it completely melts. If that takes a while there could be many rainstorms to fill it right back up. And then that water freezes.

Don’t get me wrong, it could work for several seasons if you kept a close eye on it. Until it didnt. Lol.

A solid cover would possibly help, until water/snow was on top of that pushing the pool water out the skimmer.

 

[Newdude]

The best I came up with was a high on the wall dummy return fitting / drain pipe. It could be screwed closed with a regular return plug for the really cold months but still used most of the off season.

But then I thought about the eventual puddle forming at the low spot wherever the outlet was in the yard, so both ends would need to be capped.

Then I just said ‘forget it, I’ll drain 18 inches in Dec myself’.

 

[phonedave]

Does the cover have a hole in it like a skimmer cover? If not I am assuming when there is a heavy enough rain that is completely fills the drain pipe it turns into a gravity syphon. This syphoning continues till the seal between the cover and the box dries out enough to break the vacuum.

Simple test would be to leave the cover off when it's rains and see of it happens still. If that stops it, just drill a couple of 1/4" holes in it.

If it continues to happen I am at a loss.

That is along what I was thinking. Something that creates a sort of seal. A long steady rain is enough to start a syphon somewhere. With the pump on, the draw through the connected skimmer would likely be enough to prevent the box from forming a syphon

 

[Bill1974]

I doubt the pump on or off would make a difference. Until the suction is broken, it will keep siphoning. The only ways to stop the suction is an air leak though the lid, the pool draining enough that the skimmer gets sucked empty or the over flow basin reaches the same level as the outlet of the overflow (basically they overflow pipe does not have enough flow to keep itself full and air enters the outlet of the overflow pipe to stop the suction/flow).