Free Draining Arena Base - How to Build

[RDF]

I need to re-do the base of my outdoor arena. I have found that a compacted and crowed base doesn’t drain well enough and want to create a better drainage system. I’m getting conflicting advise from contractors. My ring gets high traffic (boarding/training facility) and the natural soil is clay.

Can anyone tell me what kind of drainage pipe you have used under your arena to create french drains? Is is black corrugated pipe, PVC or something else? I don’t want to put in anything that will get crushed.

Most contractors suggest:

1. 4" pipe covered in drainage cloth every 30’
2. 4" of laser leveled, compacted, clean stone 1.5 - 2" size
3. geotextile fabric

The conflicting opinions arise after the fabric layer. Contractor 1 says to put the footing directly on top of the fabric. Contractor 2 says that a compacted stone dust base of 2-3" should go on top of the fabric before the footing. The logic is that the stone dust will protect the geotextile from the drag in case the footing moves or if a horse’s foot penetrates the footing. He is afraid the fabric will get caught and rip. Contractor 1 says the compacted stone dust will prevent water from going into the drainage layer and makes all the pipe and drainage stone useless. I can see pros and cons to each.

Anyone out there with a set up like this that works well and has held up to high traffic? Thanks in advance for any suggestions.

[ToTheNines]

I do not have direct experience with your question, but it seems like there are two theories of drainage. A hard base that the water flows over and out. Or the use of drains and mats that encourage water to flow downward.

This might be helpful – I have the footing book from Premier in front of me, which is excellent. You can get it from them for $10 with a footing sample kit. On the page with the Otto mats, it shows the following from bottom up: natural earth, sub-base?, drainage layer of crushed stone (3/8 to 5/8" stone), next the Otto mats, then a layer of fine crushed stone (1/8 - 1/4") just enough to cover the mats, then the top layer of footing.

Personally, my GUESS if I were doing a drain pipe under my footing, is to not use such a large stone over your pipes. I would use a think layer of screenings, which is what I used for my base. Very fine and will pack or not pack. Lose the fabric. Level and pack your screenings, then put down your footing, Get a drag you can set for depth. If some of your screenings get a bit mixed in over time with your footing, it won’t matter.

I think in the other parts of the country, screenings is called stone dust. The above is just my educated guess, but I have been doing a lot of reading and talking to others about footing.

I am also assuming you have explored all the options of keeping water out of the arena. And also letting water out of it.

In my case, my arena is on a slope, so I had to cut for the high long side and fill for the low long side. I graded for a 0.5 slope from the high side to the low side. There is a berm uphill of and along the high side. Plus some swales. So hopefully the only water in the arena is what falls on it. No crown, I am hoping it will all flow out nicely. It’s the water’s natural fall for this land. I am letting the base sit for a while so I can be sure after a few hard rains. I am using footboards with a gap to let water out, and behind the footboards, a run of perforated pipe in a sock to keep footing in.

I hope you get some replies better than mine that are more than just surmise. But I am not sure many people actually do drains under.

[horsepoor]

@ToTheNines

I do not have direct experience with your question, but it seems like there are two theories of drainage. A hard base that the water flows over and out. Or the use of drains and mats that encourage water to flow downward.

I agree with ToTheNines here – I think that’s where the difference is between the two contractors. If it were me, I’d want to see arenas that both had done and compare – talk to the owner/users and see how they work. Best if those arenas were ones that had been around a while to see how they perform over the seasons and time. I personally would be super reluctant to go with just footing on top of geotextile as I have seen enough horses go through the footing on my own ring and hit the base to know that would surely result in slipping and or tearing of the fabric if the ring was built that way (we did not use geotextile on mine). Especially if you have a high use barn where people and horses will almost certainly do stupid things, and not even factoring in the part about catching the fabric with the drag.

[poltroon]

Since you already have an engineered arena (I assume based on what you’ve written), I wonder if you are satisfied with the diagnosis of your current problem. If your base is truly compacted and crowned, it shouldn’t be absorbing water.

So it could be:

1. Your footing is absorbing too much water, due to its composition or thickness
2. Your base is no longer compacted, flat, and crowned. (Crown slope could be insufficient too.)
3. Water is moving on to your arena from the surrounding land
4. Water cannot move off/away from your arena because it is too low compared to the surrounding land

Your contractors have more expertise in your area and soils than I have. But these are the questions I would ask.

Whatever you do, I would look at increasing the elevation and/or crown of your arena and decreasing the elevations around it, with a clear outlet, giving the water a clear path away. Simply having a ditch around the arena isn’t enough - you want the water to go into that ditch say and then have a reason to settle/disperse many many feet away so it doesn’t seep under your base, or to have a slope away that is not at all like a ditch.

One of the outdoor arenas I’m familiar with has a pretty substantial crown – as in you can feel it when you are riding. But dang if that thing isn’t always in great shape after a torrential north coast rain.

[poltroon]

I have not experienced it with an arena but ripped geotextile fabric under an area meant to be flat is really annoying to deal with and as I understand it, rather expensive to repair in a situation like an arena. You might find out from contractor 1 if it has ever happened and if it theoretically did how it would be fixed (since I suspect it matters what kind of geotex we are talking about also).

[Horseman15]

I honestly can’t tell you much about what to put on top of the footing. What it can tell you from years of experience is you want to stay away from the black corrugated pipe. I’ve pulled so much of that garbage or if the ground and replaced it it’s not funny. I’d go with a schedule 40 PVC pipe at a minimum. There corrugated pipe is fine under light conditions, but a 1000+ lb animal bouncing on it will crush it. They use it in septic systems and for yard drains and that stuff rarely ever lasts. I just pulled all of the old pipe up at my one place that was crushed. All that ever went over that was a lawn mower. Yes, there’s a big difference in cost. But is it worth the risk? Just my opinion but I hate the stuff.

[BeeHoney]

I think that either way you have looked at there is realistically an issue.

If you lay the fabric over the larger crushed stone and the footing over the fabric, I think that the fabric would be destroyed fairly quickly. Then you would have those stones creeping up through the holes in the fabric and the base becoming uneven.

If you put down a layer of smaller crushed stone/stone dust over the geotextile fabric, the fabric would be protected, but you will have also wasted your money on all the drains because typically a compacted layer of smaller size crushed stone is relatively impervious to water. So, you might have those drains underneath, but still get puddles if the water doesn’t have a way to get through the compacted stone to the drains. If you use a larger size stone or uncompacted stone over the fabric, that stone is simply going to mix up with your footing, so that’s not an option either.

One solution to this problem is the Ottosport system. If you look at how those arenas are designed, there is a flat base of large size gravel (no fines) that is leveled that water can freely pass through. Then, special perforated rubber mats with “cups” are laid on top of the gravel. Even huge amounts of water can freely pass through the perforations in the mats and the larger size stone underneath. The cups hold just enough water to help keep the footing moist.

Another option (less expensive) would be to redo your base. A properly laser leveled (crowned) and compacted base should drain extremely well. If it’s not, I think that’s a sign that you base has become rutted, or is not as accurately graded as you think. Of course, even with a properly graded, crowned arena, it does help a lot to “seal” the arena with a flat blade prior to heavy rains.

[tl.jumper]

First the contractor who told you the screenings would set up and block the drainage is correct. Screenings have angular particles of varying sizes and they will set up super hard. The fabric over the drain pipe will also block some of the water so be careful what you use. I personally don’t like drain pipes under an arena because all french drain pipes eventually clog. If however you do put screenings over your drain pipe without fabric they will clog within 6 months.

I have had far better results putting in a correctly leveled and compacted base with a 2% cross slope. The only way to make sure it is correctly leveled is for the contractor to use dozer with a lazer leveling system. Next I have used 6 inches of Class 7 aggregate road base. Then I put in 4 to 5 inches of screening compacted. Finally come over the screenings with no more than 1 inch of sand. Do not exceed 1 inch of sand, in fact if you calculate you need 3.5 loads only order 3. Finally mix the top two inches of sand and screenings. The angular screening will stabilize the sand and the sand will keep the screenings from getting hard. The only problem with the sand /screenings is you need water to keep down the dust. However all the engineered footings need water also. From what I have seen most problem arenas have an uneven poorly compacted base, that doesn’t drain, with some soft areas and Way too much sand.

I think the OTTO mats are interesting but to to just purchase the mats themselves would be $48,000 for my 20m x 60m dressage arena.

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