Perhaps the fix is a combination of replacing the decomposed granite with rock and adding a drainage pipe underneath the fountain surround?

I have an area around my pool that doesn‘t drain well because underlying it is granite ledge. A perforated pipe was added before the small rock was added on top. The pipe helps drain excess water away from the area.

I would go with Design Fan on this. You created a not very permeable container out of landscape cloth, and filled it with gravel. A fix would be replacing it with a more correct form of drain.

@Design Fan (NE z7a) and @beesneeds As Tapla has documented elsewhere, particles > 0.1 inch / 2.5 mm do not support perched water tables. I could simply place any decent crushed rock above the landscape cloth, and the patio would hold ZERO perched water.

The landscape cloth I use drains RAPIDLY. I have multiple small patios built with gravel bases and secured on the edges with concrete, and those drain INSTANTLY and will last 50+ years.

The yard is on a slope to the street so water in the subsoil already naturally travels away, but in any case the drainage basin I created is a buffer to migration of water into the subsoil. My problem is the design above the landscape cloth, and there was an expensive lesson here to think of such situations as being just a giant container, with perched water table rules all being applicable.

The stubborn part of me still wants to find a way to make decomposed granite work as well as it can.

Ah shoot, sorry about that. I forgot that Tapla is one of the only people the OP considers intelligent enough for advise around here. My bad for not paying enough attention to the topic poster, please disregard my previous post.

Tapla is pretty awesome, so I can understand.

@tapla (mid-Michigan, USDA z5b-6a) The decomposed granite is the walking surface. I added a simple schematic to the original post, and I am copying that here as well.

The total area is small, let's call it about 100 square feet.

It would be difficult to grade the surface underneath the decomposed granite. I'm not sure that would be less work than other solutions, and my guess is that it won't fix the issue well because the small particle sizes in the DG create a strong capillary action/adhesion/cohesion. In other words, grading the subsoil/surface under the DG helps but does not really "fix" the problem.

As I see it I have a few ways to go on this:

1) I can replace the DG with crushed rock that has particle sizes > 0.1 inch / 2.5 mm, and the problem instantly disappears as there will be no perched water. The person who wanted DG will throw a fit, but that's my problem.

2) I can amend the DG with some other crushed rock, trying to greatly reduce the perched water in the mix. For example, I have a beautiful gold 3/4" crushed rock, and I could try to densely pack that and let the DG fills spaces between those rocks. There would still be a lot of DG. Getting specific, tightly packed 3/4" crushed rock has about 30% to 40% void space between the rock. That's all space that the DG is going to fill. Having my mix be 30% as decomposed granite is probably not going to avoid perched water?

ChatGPT suggested this mix:

55-60% primary 3/4" crushed rock as the base.

25-30% intermediate filler like 3/8" crushed rock (#8).

10-15% fine sand or 1/8" screenings for further void filling.

Less than 5% DG to act as a binder but not create perched water.

How would you change that?

3) I can add wicks throughout the patio, but I think this, at best, speeds up the drainage of the perched water, but doesn't really avoid the fact that the patio will be a muddy mess for many hours.

4) I can add wicks and also increase the depth of the decomposed granite to 10+ inches, to put the perched water far below the surface of the patio. That's a lot of work.

@beesneeds No, I don't think Tapla is the only one who can answer this question. I was simply pointing out that I don't have a drainage problem underneath the landscape cloth that holds the decomposed granite. All of my problems live above that landscape cloth, in a perched water table created by lots of really small particles in the decomposed granite.

My drainage set up has been successful for years so I know my suggestion works. Good luck.

@Design Fan (NE z7a) Drainage Pipes / French Drains are great. I use them in other places. I could add one here too. But the problem I am describing in this post is not about carrying water away from the patio area to another place. The problem I am describing is that water is binding into the decomposed granite and creating a waterlogged layer that cannot be removed by a simple drainage pipe.

You are right that I could replace the decomposed granite with rock. That was one of the possible solutions I am looking at.

The landscape cloth I use drains RAPIDLY. I have multiple small patios built with gravel bases and secured on the edges with concrete, and those drain INSTANTLY and will last 50+ years.

Looks like you found your solution!

@w0lley32 Sure, I have the option to use rock for the patio surface instead of decomposed granite. That's one possible solution.

My question was trying to find a way to get a patio made with a decomposed granite surface to drain better, and to minimize perched water, without abandoning decomposed granite.

Just for kicks, I put 10 inches of decomposed granite into a container and filled it. The water is draining about 1/2 inch per hour. After three hours, it's still a lake!

Returning to this topic, it might be worth pointing out the difference between geotextile fabric and landscape cloth. Geotextile fabric is nonwoven and more industrial-grade. Water passes through it rapidly, but it prevents substrates on either side of the cloth from mixing. It is used in roadways, commercial patios, and any kind of construction work where you want to keep drainage layers separated from subsoils. Geotextile fabric that is nonwoven is what I used,

Landscape cloth is the cheap stuff that is sold at stores like Home Depot. It's typically a woven fabric and drains slowly. Gardeners sometimes use it as a top layer below bark mulch. I hate that application of it, but in any case, landscape fabric is a poor choice for use at the bottom of a crushed rock layer to separate it from the subsoil.

I assume resurrecting your thread means the DG is still ponding and sloping the surface was not chosen as a solution.

It is unclear if the "ditch" you describe gravity discharges anywhere. If it is just dug under the DG area with no where for the water to move to, then it is just a bathtub if your surrounding subbase soil is clayey. Realize that water enters this "ditch" not just from the DG above it, but simultaneously from the surrounding soil when the soil becomes saturated during times that the DG is waterlogged (during rain).

You also don't state the type of 4"-8" deep rock in the "ditch," whether it's clean and the AASHTO designation. Those are critical specs.

DG will harden enough to have properties similar to concrete. But, it will still allow water to pass, as your container experiment testifies. If you do have a french drain below the DG (that's exactly what the "ditch" you've created technically is, as long as it can discharge somewhere), then the DG will drain, and a bit quicker from capillary action.

A term that is not mentioned here nor did I see it in the quick skim of Tapla's post, is sieve. That is what is being described in a round-about way.

@3onthetree I removed the DG entirely, and I replaced it with 3/8 crushed rock held horizontally by a plastic grid.

The 4" to 8" rock is crushed rock from a local quarry. I don't know the AASHTO rating, but conservatively there would be about 30% void space between rocks.

Consider the math behind the "ditch" under the patio. That ditch is 100 cubic feet (10 x 10 x 1), which is a little less than four cubic yards. If 30% is void space, that is about 30 cubic feet. It's a huge volume of water. That's equivalent to a massive downpour of rain at a rate of one inch per hour for 4 hours. After the rain stops or slows, the water drains into the subsoil at a normal rate. So the ditch is a buffer, and a massive buffer, and it would be a once-in-10-year event for that buffer to overflow.

I did connect the drainage ditch to a new French drain system, so it's all a moot point anyway.

Where I would push back is on the issue of DG draining. This misses the entire point. Because of its fines content, DG has an enormous perched water table. The perched water layer is about six inches thick, which means that even if I had an entire swimming pool of void space and multiple gigantic French drain systems, that six inches of perched water would form a stable reservoir on top of the DG that does not drain quickly. Some is lost to evaporation. The actual drainage rate is slow. My experiment with the DG in a container showed that the lake of water on top of the DG remains in place for days, not minutes or hours.

The importance of Tapla's work here is that it exposes the physics of perched water. The capillary action that holds water at the bottom of a container is independent of the drain hole's size. It's an intrinsic property of small particles in the soil mix.

I didn't miss any point, except what the purpose of this thread was. It seemed you still had a problem, and I was trying to solve it. Guess that's not what this was meant for, so carry on.

@3onthetree I never posted to the thread about my decision to replace the decomposed granite until today. I should have included that update in my prior post, and I apologize for any misdirection.