Pool Pad Rainwater Drainage

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aaronb97

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Apr 21, 2024
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Nashville, TN
I'm thinking about building an above ground pool on an elevated pad with trenches surrounding it for rainwater drainage. Our backyard is very flat and we get heavy rain sometimes resulting in lots of standing water. It does flow in one direction, just pretty slowly.
Due to the lack of any notable "high ground" on my property, I was thinking the best way to prevent standing water under the pool might just be to simply elevate the pad a few inches above grade and collect excess water in a trench around the pool leading to a low point where it could drain into the ground.
I attached a picture showing my vision. Is it overkill?

Just looking for advice, best practices, and I'm not married to the arrangement laid out above. Totally open to better options.
 

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The issue is that a pool full of water weighs alot!
For instance- my 26k gallon 33’ round pool weighs approximately 217,000 lbs.

It’s expensive to build a pad that accommodates that.

Whats wrong with normal drainage methods like french drains that direct water away from the pool area?
They’re not as cool as a pool surrounded by a mote but I suspect that would become troublesome anyway.
 
Mdragger88 said:
The issue is that a pool full of water weighs alot!
For instance- my 26k gallon 33’ round pool weighs approximately 217,000 lbs.

It’s expensive to build a pad that accommodates that.

Whats wrong with normal drainage methods like french drains that direct water away from the pool area?
They’re not as cool as a pool surrounded by a mote but I suspect that would become troublesome anyway.
Click to expand...
Apologies for not clarifying this earlier. The 3d model depicting a “mote” is misleading. That is my idea of an encircling french drain. (the tops being open is just lazy modeling). In reality, i’d love there to be a french drain surrounding the pool pad that’s capable of handling large amounts of water quickly. When it rains it pours.

How would you approach french drains taking water away from a pool pad, if encircling it isn’t the proper way?

Thanks!
 
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Encircling with a french drain is the way - so you’ve got the right idea there. Just not sure about the feasibility of a concrete pad. If you’re going to build up in any way I do know that using what they call “crusher run” well complacted under the pool is recommended but building up the base is generally not ideal.
If you are dealing with elevation differences (house higher than the pool) a retaining wall may be a better choice with some drainage infront of it as well.
Think layers to redirect water.
The first layer would be the french drain infront of the retaining wall then another encircling the pool.
Here’s my terribly crude depiction 🤣
IMG_9738.jpeg
What size pool are you planning on having?
 
What I mean about the concrete is that it must be designed/engineered to handle the weight- this can be expensive. More expensive than the pool. The pad is also much more permanent than the pool. That’s why most people don’t take that route.
It also needs to cure before putting the pool on top so you want to speak to an experienced concrete professional to make sure you cover all your bases.
Even with concrete if there’s elevation differences you should have a retaining wall like in my fancy picture to prevent as much runoff as possible on the pad .
Its not that its an inherently bad idea- just expensive & more complicated.

Here’s a good thread where a member did similar to what you’re proposing- concrete prices were quite a bit lower at that time though.

Installing an above ground pool on a concrete pad

Looking for advice on installing a pool on a concrete pad. The pool is a Sharkline Matrix 24' round. I have purchased padding and coving for the bottom. The concrete pad is level to 1/4 inch. Has anyone tried this?? Any reason it won't work? Any help would be appreciated. Thanks!
www.troublefreepool.com www.troublefreepool.com
 
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Mdragger88 said:
What I mean about the concrete is that it must be designed/engineered to handle the weight- this can be expensive. More expensive than the pool. The pad is also much more permanent than the pool. That’s why most people don’t take that route.
It also needs to cure before putting the pool on top so you want to speak to an experienced concrete professional to make sure you cover all your bases.
Even with concrete if there’s elevation differences you should have a retaining wall like in my fancy picture to prevent as much runoff as possible on the pad .
Its not that its an inherently bad idea- just expensive & more complicated.

Here’s a good thread where a member did similar to what you’re proposing- concrete prices were quite a bit lower at that time though.

Installing an above ground pool on a concrete pad

Looking for advice on installing a pool on a concrete pad. The pool is a Sharkline Matrix 24' round. I have purchased padding and coving for the bottom. The concrete pad is level to 1/4 inch. Has anyone tried this?? Any reason it won't work? Any help would be appreciated. Thanks!
www.troublefreepool.com www.troublefreepool.com
Click to expand...

Crusher Run! That sounds like it fits the bill for what I was looking for. Something that compacts well, while still allowing for good drainage.
Regarding concrete, I don't intend on going down that road. Too pricey for me! My 2D cross section had "Gravel" as the placeholder until a more ideal solution was proposed and I think crusher run sounds like that solution.

As far as elevation goes, the entire property is flat. The house has a very shallow crawl space that descends below ground level so I definitely don't want to route excess rainwater toward the house and risk flooding the crawl space. That's probably another topic for another forum, but it does raise an eyebrow for me. Maybe I need to include a French drain between the house and the pool no matter what, as your drawing nicely depicts :D

My follow up questions to that would be:
  1. Should the pad be elevated at all, or should it be level with the ground?
    1. I'm assuming that the retaining wall idea stems from the pad being elevated...
  2. How thick should the crusher-run layer be, whether its fully sunk into the ground, or partially proud of ground level?
  3. Should the crusher run be topped with sand and/or foam layer for puncture protection?

Thanks again!!
 
aaronb97 said:
My follow up questions to that would be:
  1. Should the pad be elevated at all, or should it be level with the ground?
Click to expand...
You don’t necessarily need a “pad”.
The ground can be leveled (dig down to level) & you just add a sand base or gorilla pad, pavers under the uprights & call it good if you like. Most above ground pools are installed this way.
You just cannot build up the ground with dirt to level things out - you either must dig everything out until level or use a base of “crusher run” that is well compacted.

How to level above ground pool - Further Reading

www.troublefreepool.com www.troublefreepool.com

aaronb97 said:
    1. I'm assuming that the retaining wall idea stems from the pad being elevated...
Click to expand...
I was under the impression there were large elevation differences between your home/yard & where the pool will go.
If this isn’t the case you really don’t need a retaining wall. You just must make sure water drains away from the pool area.
aaronb97 said:
  • How thick should the crusher-run layer be, whether its fully sunk into the ground, or partially proud of ground level?
Click to expand...
Most people do at least a couple inches- type in the search bar “crusher run” & “gravel under above ground pool” to see where/how people have used it as their base. There’s quite a few build threads around here.
Also it’s important to know what pool you intend to purchase. Some state thickness of gravel base in the instructions.
aaronb97 said:
  • Should the crusher run be topped with sand and/or foam layer for puncture protection?
Click to expand...
Many top it with stone dust, compact more then proceed with their foam or sand pool bottom.

Gravel Around Pools - Further Reading

www.troublefreepool.com www.troublefreepool.com

Maybe @phonedave can help a little more with the details as my pool is not constructed this way
 
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It is not recommended to build up the base for an above ground pool because it is not as easy as it sounds. There is a science to compacting fill. A pool is VERY heavy, quite unstable, and needs to be pretty close to level.

As a very high level summary, each and every fill has a different compaction curve, and what is called an optimal moisture content. If you have more or less water than is optimal, you will never get it to its densest potential. You can compact it with the heaviest machinery and once it gets to the optimal moisture content it will compact some more. It has to do with water acting as a lubricant up to the point where it then starts taking up space in the soil matrix.

The point is, unless you run what are called Proctor tests on your fill, you will not know what is called the maximum dry density. And unless you run in-field tests, you will not know how close your compacting efforts have come to achieving this.

As far as Crusher Run is concerned (is is also known as QP, Quarry Process, DGA, Dense Graded Aggregate, and about a half dozen other names depending on your area), it is a very forgiving material. The compaction curves are pretty flat, meaning there is a wide range of moisture contents where you can still hit that magic 95% of maximum dry density.

However, you still have to do it right. Get it close to the optimum moisture content, 4" lifts max (less is better), hit it with a HEAVY vibratory plate compactor with multiple multiple passes (no Jumping Jacks, and absolutely no hand tampers)
 
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Mdragger88 said:
Many top it with stone dust, compact more then proceed with their foam or sand pool bottom.

Gravel Around Pools - Further Reading

www.troublefreepool.com www.troublefreepool.com

Maybe @phonedave can help a little more with the details as my pool is not constructed this way
Click to expand...


  • 3/4" clean (what everyone calls "gravel" in some spots (mainly for drainage in areas you cannot see)
  • 3/8" grey pea gravel in some areas - like under the swing set.
  • 3/8" yellow pea gravel around some trees
  • 2" egg rock around the pool. It is large enough to stay in place, but it nests well. The rounded edges make it easy to pull any stray weeds that get into it.
  • Pea gravel is most often recommended for the base of fiberglass pools. Get a tamper in there on the base material, and compact in lifts.[2]
  • Pea gravel gets everywhere - it is too small to put around the pool. It gets knocked out of wherever you put it too easily. It works great under a swing set, because a good layer of pea gravel provides a cushioned surface for around swings and play structures.
  • Eastern Sunrise is pretty, it is it like volcanic rock. It is unstable to walk on, and dogs hates it (it hurts paws). It is also a pain to weed in (because it is so sharp)



I wrote this in a post - no idea why it is part of that article. This was a list of rock I have around my property and where. Not all (or any) of it should be under a pool

I also just had 2.5 yards of 3/4" clean stone dropped off to fill in under the floor of one of my sheds. Rock everywhere!

Also the pea gravel swing set area is now a raised garden bed area (the pea gravel is still there as paths.)
 
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@phonedave Excellent information, thank you for the detail - Hoping to be able to now refine a general checklist from here.
From what you and MDragger have said so far, it sounds like what I should do is something like this (italics represent things we haven't talked about yet):

  1. Dig a circular grass clearing, probably no more than an inch or two down, and maybe 2 feet larger in diameter than the incoming pool (thinking the resulting 1 horizontal foot of gravel surrounding the pool will help with excess water runoff, but please advise)
  2. Order enough Crusher Run to fill the circle, repeatedly compacting and leveling
  3. Place pavers where the pool legs will go
    1. How do I make sure the inner corners of the pavers don't press into the pool liner?
  4. Fit a foam pad / gorilla pad on top of the gravel, with cutouts that allow for the pavers to fit without causing unevenness.
  5. Build the pool?

I just had 811 come out and mark the property for conflicts, none were found, so we're almost ready to start.
 

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aaronb97 said:
@phonedave Excellent information, thank you for the detail - Hoping to be able to now refine a general checklist from here.
From what you and MDragger have said so far, it sounds like what I should do is something like this (italics represent things we haven't talked about yet):

  1. Dig a circular grass clearing, probably no more than an inch or two down, and maybe 2 feet larger in diameter than the incoming pool (thinking the resulting 1 horizontal foot of gravel surrounding the pool will help with excess water runoff, but please advise)
  2. Order enough Crusher Run to fill the circle, repeatedly compacting and leveling
  3. Place pavers where the pool legs will go
    1. How do I make sure the inner corners of the pavers don't press into the pool liner?
  4. Fit a foam pad / gorilla pad on top of the gravel, with cutouts that allow for the pavers to fit without causing unevenness.
  5. Build the pool?

I just had 811 come out and mark the property for conflicts, none were found, so we're almost ready to start.
Click to expand...
If you dig down to undisturbed soil, there is no need to add a base of compacted crusher run, sand will be fine.

Dig down, level, add sand. Pavers get set flush with the top of the sand, so they will be recessed into the ground. They will not press into the liner. A cover (sand or foam) has to go in the inside corner of the pool, further covering the pavers.

No cutouts in the pad for the pavers, the pavers need to be flush.

If you want you can dig a trench OUTSIDE of the pool footprint, 8-12 inches deep, line it with a geotextile, fill it with 3/4" clean, wrap the geotextile over the top, add the desired ground cover of your choice. Then on the low side add a drainage pipe, daylighting to somewhere on your property where you do not mind the water.
 
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phonedave said:
If you dig down to undisturbed soil, there is no need to add a base of compacted crusher run, sand will be fine.

Dig down, level, add sand. Pavers get set flush with the top of the sand, so they will be recessed into the ground. They will not press into the liner. A cover (sand or foam) has to go in the inside corner of the pool, further covering the pavers.

No cutouts in the pad for the pavers, the pavers need to be flush.

If you want you can dig a trench OUTSIDE of the pool footprint, 8-12 inches deep, line it with a geotextile, fill it with 3/4" clean, wrap the geotextile over the top, add the desired ground cover of your choice. Then on the low side add a drainage pipe, daylighting to somewhere on your property where you do not mind the water.
Click to expand...

Mostly makes sense. My only concern with not having crusher run is water drainage. Our backyard is notorious for flooding so I fear sand will quickly erode in my case.
Wouldn't a few inches of crusher run provide a base capable of better water drainage?
 
aaronb97 said:
Mostly makes sense. My only concern with not having crusher run is water drainage. Our backyard is notorious for flooding so I fear sand will quickly erode in my case.
Wouldn't a few inches of crusher run provide a base capable of better water drainage?
Click to expand...
Crusher run well graded mixture running from stone dust up to 3/4" aggregate. Well graded means there is about an equal amount of all aggregate sizes in between. It packs solid like concrete. It barely drains at all.

It also does not wash away, but water is not going to drain through it.
 
phonedave said:
but water is not going to drain through it.
Click to expand...
Oh, I was under the impression that it had better drainage properties than that. Thanks for educating me there.
Maybe the more important question is: Does the base need to have good drainage properties?

What if the base was solid crusher run (topped with gorilla pad or similar for liner protection), expecting water to pretty much run off of it, and the pool was surrounded by well-planned French drains to handle the water drainage?

As you can see, my main concern is making sure my base doesn't shift during rain storms. The yard tends to hold water so I need whatever's supporting the pool to be as erosion-resistant as possible.
 
aaronb97 said:
Oh, I was under the impression that it had better drainage properties than that. Thanks for educating me there.
Maybe the more important question is: Does the base need to have good drainage properties?

What if the base was solid crusher run (topped with gorilla pad or similar for liner protection), expecting water to pretty much run off of it, and the pool was surrounded by well-planned French drains to handle the water drainage?

As you can see, my main concern is making sure my base doesn't shift during rain storms. The yard tends to hold water so I need whatever's supporting the pool to be as erosion-resistant as possible.
Click to expand...
That is what I was going for in my description. Make a solid base, it should be flat and level. Put a french drain system with the proper fall around it.
 
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@phonedave has you covered on the ground stuff.
For my pool they used rectangular pavers- 7.5” x 15.5” they were not as thin as the ones you buy for a dollar or two to make a walkway. As he said, Their tops should be flush with the compacted ground the pool sits on. After the wall is up, There should be a built up cove around the inside of the pool- either sand or foam. This reduces some of the pressure from that area so the liner doesn’t get pushed under the wall.
This will also ensure the liner never comes in contact with the pavers.
Unfortunately I don’t have any pictures of that part of my build.
The pool you buy will have instructions with exact dimensions that lay out where the pavers should go & possibly what should be used.
 
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