Pool Surround Drainage Questions

[tony]

Hi all. Hope you've all been good since I was here last, probably not but what else is new. I love yiz anyway.

Outside of still recouping from back surgery near a year ago now I've been busy hiring contractors to do the work I'm no longer capable of doing. The most recent is having a new retaining wall and slab built in my back yard. I live in a typical track home here in SoCal and a corner lot at that. What we're doing is creating additional deck/patio space for chairs and what-not to the back side of our pool. When the lot was built no drainage to the street was established, so it's too late and way too costly to consider that with all the concrete to go under and neighbors yards to go through, so forget that. What I need to come up with is a way for the winter rains and excess pool water to drain off to rather than collecting and being trapped on the new slab. If there's no drainage the the new area will fill very quickly.

I've been considering the long grate type of drain that would run the length of the slab. This way it could look nice and be effective. The problem is that I haven't seen any that has holes in it that could allow water to drop straight down. I figured that it could drop into crushed stone a few inches below the grate. The grate would be set to the back most part of my slab, correct? Which way would best make sense for the slab to slope, back or front?

Would this work? Other ideas?

Pics below show where the wall and slab would be. Don't mind my stiching, it was fast and dirty.

Thanks for any help.

[TDHofstetter]

I'd think... the slab would slope toward the grate, draining anything you want drained into the grate, and slope away from the grate to drain anything you want to drain elsewhere. Doesn't look like there's much "elsewhere" 'round them parts, so...

On second thought, how do you feel about draining some of it directly into the pool? If that's OK, then slope everything between the grate & the pool toward the pool. That'll save grate drainage for the stuff that MUST go into the grate.

[tony]

Hey Tim. Thanks for the reply.

Having it spill into the pool isn't an option since the tile grout would easily get stained from any dirt that's brought in by the water and we get lots of dirt blowing here in the early part of the year.

As for the slope what I meant was, should the grate be at the back of the cement area and slope back towards that or be at the front of that area (closer to the pool) and have it obviously slope towards that? I know that this may sound paranoid, but should I consider sub earth corrosion of any kind with this type of drainage around the pool (below the cement level)?

[TDHofstetter]

Ah. I see.

Do you have good sandy soil that can take up that drainage & not just fill your drain?

If it were me... I think I'd put the grate someplace around the middle & have it slope both ways. That way the slope on each side isn't as extreme. Not that it'd be very extreme, in a narrow spot like that... maybe it's just the symmetrical part of my head getting in the way.

I doubt seriously that the moisture will cause any problems with the pool. One serious thing to think about, though, is pressure - any excavation near the pool will remove the pressure that's keeping the pool held together, and it may blow outward if it's full at the time. When ya put it back, tamp the CRAP out of it to restore the soil pressure.

Along that line... the deeper your drain system is, the farther I'd put it from the pool. If it's only a foot or so deep, I'd feel OK about putting it right near poolside. If it's four feet deep I'd put it as far away as possible.

Now... what're the chances of somebody wanting a chair or chaise longe along that back side? You might want the grate far from the pool so chair/longe legs don't get caught in it.

So... far? Sloped away?

[dcarter636]

I would think real hard about making a 6"x6" concrete trough gutter and covering grate at the boundary with the original pool decking. When you get serious rain fall a deep gutter will capture most of the organic stuff before it washes into the pool, and you can open it up and use a hoe to remove the dirt and crud that accumulates, without crawling around on hands and knees.

We had a similar planting near our pool and tunneled under a block wall to lay a 3" drain pipe chanelling the runoff under the front lawn to the driveway. Leaves, bark, and heavy landscape debris costs way too much in chemical maintainence once it gets into that cement pond.

[tony]

Do you have good sandy soil that can take up that drainage & not just fill your drain?

Yes and plenty of it. Very good seepage.

If it were me... I think I'd put the grate someplace around the middle & have it slope both ways. That way the slope on each side isn't as extreme. Not that it'd be very extreme, in a narrow spot like that... maybe it's just the symmetrical part of my head getting in the way.

I like that idea, but I imagining a small cement-type table with benches, sometime in the future, being there also. If the slope were to meet in the middle the table idea may not work because of a possible rocking. I'd like to keep options like this open.

I doubt seriously that the moisture will cause any problems with the pool. One serious thing to think about, though, is pressure - any excavation near the pool will remove the pressure that's keeping the pool held together, and it may blow outward if it's full at the time. When ya put it back, tamp the CRAP out of it to restore the soil pressure.

Gotcha.

Along that line... the deeper your drain system is, the farther I'd put it from the pool. If it's only a foot or so deep, I'd feel OK about putting it right near poolside. If it's four feet deep I'd put it as far away as possible.

I was just a Lowes and looked at their channel drains. They had one that I may consider. It's about 5 inches deep. If I were to put it to the very back of this new area it would be about 8.5' from the pool, how deep would you say the trench would have to be under the drain itself? The following is what I imagine, what would be sufficient for the space, gravel and soil?

grate 5"
air space ?"
gravel ?"
soil

The only down side of what I saw at Lowes is that it had no holes running along the length of the drain. It's PVC, so I could drill my own. If you were to guess what size holes would suffice and how far apart?

Now... what're the chances of somebody wanting a chair or chaise longe along that back side? You might want the grate far from the pool so chair/longe legs don't get caught in it.

Exactly. That why I'd like it on either the back or the front, I'm leaning toward the back side.

So... far? Sloped away?

Huh?

[tony]

Jun 3, 2010 18:12:20 GMT -6 dcarter636 said:

I would think real hard about making a 6"x6" concrete trough gutter and covering grate at the boundary with the original pool decking. When you get serious rain fall a deep gutter will capture most of the organic stuff before it washes into the pool, and you can open it up and use a hoe to remove the dirt and crud that accumulates, without crawling around on hands and knees.

Would the PVC type work just as well with the way I described above?
What Type of grate could I use to cover the "concrete trough gutter"?
Also remember that it has to drain straight down and not out to another location, so how can trough work for me?

We had a similar planting near our pool and tunneled under a block wall to lay a 3" drain pipe chanelling the runoff under the front lawn to the driveway. Leaves, bark, and heavy landscape debris costs way too much in chemical maintainence once it gets into that cement pond.

Wish I could go that route, but way to costly. I'm basically boxed into the back yard.

[dcarter636]

I imagine PVC would hold up fine if it was protected from the sun. There are industrial grate strips for covering drain gutters in wet factory environments, what's available would dictate the design of your gutter, I don't know where to find them, but Graingers is the first place I would look and McMaster-Carr would be second.

I was not thinking in terms of drain down, we lived with adobe clay soil where that would be a disaster for the concrete as the clay swelled and shrunk with the seasons. If you have sandy soil then draining down through a 0-3/4" sand-gravel bed should work well. Have you checked to see what free drainage info your local building permit office has?

[tony]

I imagine PVC would hold up fine if it was protected from the sun. There are industrial grate strips for covering drain gutters in wet factory environments, what's available would dictate the design of your gutter, I don't know where to find them, but Graingers is the first place I would look and McMaster-Carr would be second.

I saw this type (Item #: 110877) at Lowes today, but the one I saw allows the actual grate to pop off.
www.lowes.com/pd_110877-676-864G_0_?productId=1119169&Ntt=%20channel%20drain&Ntk=i_products&Ns=p_product_price|1&pl=1¤tURL=/pl__0__s?newSearch=true$Ntt=%20channel%20drain$y=0$x=0

[/quote] I was not thinking in terms of drain down, we lived with adobe clay soil where that would be a disaster for the concrete as the clay swelled and shrunk with the seasons. If you have sandy soil then draining down through a 0-3/4" sand-gravel bed should work well. Have you checked to see what free drainage info your local building permit office has? [/quote]

I'm about to check with them when I get my permit. A contractor that was out to bid told me all about the wall construction including rebar and footing requirements, but not drainage, so I'll have to check. Lately we've just been dealing with hauling a ton of dirt away and the demo of the old 3' wall and footing.

Edit in:
Just found this also:
www.ndspro.com/trench-drains-and-channel-drains/channel-drain/pro-series-channel-drain-system/

Since there's a drain hole on the bottom of each, I really wouldn't have to modify anything. I'd just let each hole drop water right into the gravel pit, correct?

[dcarter636]

That looks alot like what I was suggesting, but easier to install.

With the downspout feature on each 1 meter section, that appears to provide everything a fellow could want for direct drainage and debris capture.

[TDHofstetter]

Well - THAT looks like it's wrapped up now!

Only thing left is a little calculation - it's time for you to do something nearly every Vermonter pays someone else to do at least once - "perc test", or percolation test. First, a little homework. Find out what the single heaviest rainfall in recent record (say 50 years) dropped in inches of water. Divide by 12. That's your "depth", in feet. While you're there, find out how long that storm lasted.

Now figure how many square feet of land surface you're planning on draining into that drain. That's your "area".

Multiply area by depth to get cubic feet of water per maximum rainfall. That's your "capacity", how much water your drain may have to store in worst case.

Now it's time to do the perc test. Dig a hole in that area. Make it as nearly as possible one foot square and one foot deep. Have someone start timing you just as you begin to pour THREE gallons of water into the hole. Have them stop timing when the hole no longer has any puddle in the bottom. Divide by three - that's your perc rate, in minutes/seconds per gallon. Expand that to gallons per hour.

Start with the "capacity" in cubic feet you figured earlier - that's how big a concrete hole would have to be if it was going to store a bad bad rainstorm... but the perc rate is how fast your ground can keep up with the rainfall, so you can downsize the capacity according to your perc rate. Go back & see how long the storm lasted in hours, and divide your capacity by hours to get cubic feet per hour. Multiply by .134 to get gallons per hour. Subtract your perc rate in gallons per hour to get your "overfill". Multiply again by the storm's duration in hours, and you wind up with total gallons you have to store in the gravel pit under the grate. Figure rock is going to give you about 50% fill, so double that storage capacity & you have your drywell size.