Adventures in Culvert Drainage for my Horse Paddock

For those of you that live in rainy climates (like the Pacific Northwest or the U.K.), or, maybe you get a really intense rainy season that lasts for a couple of months, then you know how nasty your paddock and pastures can get from the drizzly onslaught.

So let me take you an a little pictorial journey through my experiments over the last couple of years, to try and prevent my big covered barn in BC, Canada, from turning into THIS every Spring/Winter/Fall:

Inside my big barn in the Winter

I’m going to share my experiments with you, and also what I’ve learned – to hopefully shortcut your own learning curve and give you some solid tips to follow if you’re faced with a similar situation.

What wants to happen?

The first step in figuring out how to create effective drainage – via culverts, trenches, or other means – is to first do nothing. And just study your land. If you have the luxury of simply watching your land for an entire year (to observe a complete cycle of the seasons) that is the absolutely the best course of action and will save you plenty of time and money.

Of course, you could also call in someone like Sarah Lockwood; who would be able to assess your property from a geological standpoint and ‘read’ your land like an open book. And when I do buy my own land, I am definitely consulting Sarah! But for us mere laypeople, or those of us who are boarding, giving the land time to show you what naturally wants to happen each season is definitely the wisest plan.

Let’s take the simple example of my barn. After we cleared a decade of junk out of the main barn, this is what was left. This picture was taken in the late summer (for those of you who are regular readers, that is Kesia’s horse Spero up on the ledge). You can see that the paddock outside the barn – even before it was graveled – is higher than the barn floor. So guess where the water’s going to go when it rains?

The big barn in late August
The big barn in September

And then we look at the paddock itself – you can see that it is naturally sloping down towards the barn, the field, and the blackberry patch on the left hand side:

Aude gets a trim and Kesia gets a massage in the paddock

So the first decision was to simply not gravel the blackberry area. We cleared half of the blackberry bushes out, but then left it bare so the water could congregate where it naturally wanted to go. Interestingly, the horses then turned this bare area into a pooping area.

We cleared half the blackberry bushes and then just left it alone

For the main barn – and the sloped-roof area right next to it, where I store my hay – a drainage solution was definitely needed. The first winter I simply dug a culvert along the side of the graveled paddock; to draw the water down and out to the field.

Hand-dug culvert along the side of the graveled paddock

Tip: If you can, dig your culvert during wet weather, because then you will be able to see instantly if the path you’re digging is where the water naturally wants to go. You will also be able to determine whether you have dug your culvert with enough of a downslope for the water to flow easily.

A shovel with a pointed tip works best and you may need a pickaxe as well

A culvert or trench should not just be a flat trough; you need to have it higher at the intake point and lower/deeper at the outflow or exit point – with the culvert gradually sloping downwards between the intake and exit. Water flows best downhill!

The problem with this simple culvert solution is that – silly me – I thought the horses would just step over the culvert, when going in and out of the big barn. And they did not. They destroyed the culvert. So I experimented by laying 2×12-inch boards across the top of the trench – which my 1800 lb Belgian would then step directly on top of, and either squish the boards down, or tilt them sideways.

My attempt to protect the culvert

Round two…

So after re-digging the culvert 5 times (takes at least an hour each time) I talked with my tractor guy and he suggested filling the trench with river rock, so the horses could step on it, but the water could still drain through the rock. Here’s what river rock looks like:

River rock – so water can flow through the rocks

And here’s the culvert filled with river rock:

River rock-filled culvert alongside the layers of gravel in the paddock

Did this work? Hell no. The herd simply churned up the gravel and river rock together until it was a solid mess and there was no more drainage to be had!

Keep in mind, I do not have sedate, slow-moving horses. I have 4 horses under age 4 and they tear around, wrestle, leap, and skid sideways on my gravel, like this:

Round three…

The following Fall I decided to also put some gravel down on the dirt floor inside the big barn to help keep it drier and the excavator guy I hired had the idea to lay some sewer drainage pipe in the culvert in front of the barn, and then cover it over with gravel. Sounds like a plan to me!

First step was to remove the soft dirt/mud from the floor of the barn:

Removing soft dirt to get down to hard pan before laying the gravel

This is the very inexpensive pipe we used from Home Depot (needs to have holes along the sides, and when you lay the pipe, the holes should face down):

And here it is in the culvert in front of the big barn entrance – this is the passageway that gets the most traffic.

The length of drainage pipe in the culvert in front of the big barn – holes on the bottom

You can see this drainage pipe will be able to handle the horse’s weight no problem!

If this pipe can withstand an excavator, it will hold up under my Belgian!

And here’s what it looks like all finished and ready to solve my wet barn problem:

Drainage pipe installed and graveled from the paddock to inside of the big barn

But… NOT!

By the time we hit the end of February (5 months after installation), here’s what it looks like:

Not draining so well after all

The barn inside is not flooded, but there are a few wet spots. The worst spot has about 2 inches of mud – the gravel has just been churned into the dirt underneath. Overall it feels damp/soggy when you walk around, but it looks okay in most places, for example:

Mostly ok, but you can see some of the wet and muddy places

Round four…?

So, this sort of solved my drainage problem… but had it all be done correctly, I think it would have worked brilliantly! As they say – god is in the details. After my own learning curve, along with copious further research, here’s what I should have done, and will definitely do differently next time:

1. Adequate, Smooth Slope

Getting the culvert dug with that downward slope we talked about is of crucial importance! Then, when you lay the pipe in the culvert, you need to double-check that the pipe is not being pushed up at any points by stray/buried rock, or a wedge of dirt that’s higher than the rest. This culvert did not have enough of a downslope and it was also not a smooth downslope. I really should have done some hand-digging to make it better. But the excavator guy said it was fine and (doh!) I listened to him.

In all honesty, it’s really hard to override these macho guys who are also supposed to be the expert. But next time, I will send him away for 15-30 minutes, or get him to take a break, so that I have the time and space to really look at the slope, pipe, etc. and listen to my own body wisdom (who has dug more than a few culverts!). And unless you’ve got balls of steel (hey, ovaries are balls!), you can’t do this with him watching you! Seriously, it’s super important to get the guy to take a break (send him off to work on something else if you can) so you can take the time and space to tinker and get this perfect.

If you don’t believe me as to how important this is, then check out this quote from the ADS Drainage Handbook:

“The alignment or line of the pipe is the horizontal location of the pipe, while the grade is the vertical slope of the pipe. In order for a pipe system to function as designed, it is important to install the pipe to the proper line and grade.”

After watching numerous drainage videos on YouTube, I finally found someone who’d done the math!

So my culvert is about 50 feet total, divided by 8 = 6.25 inches. So that means my intake point should have been 6.25-inches higher than the drain’s exit point. In reality I think it is only about 4 inches higher, but, the slope of the trench under the pipe is also not even – I could see that as he was covering it with gravel.

And how do you check your slope?

2. Lay Enough Pipe

I should have laid pipe the entire length of the culvert – from the intake point before my hay storage, to the exit point out in the field – not just the area in front of the barn. When the excavator guy told me to get pipe, he didn’t tell me how many to get, so I just got 2 pipes. I should have halted work and driven back to Home Depot to get more pipe.

Note: the pipes fit together easily by just inserting the smaller end into the slightly larger end.

Now that I’m thinking about it, I realize that to get an accurate downslope in that culvert all the way from intake to exit, so the pipe lies evenly in the trough, I would need to allow about 45 minutes to an hour of hand-digging/smoothing time. And then I would test it first, by pouring water at the intake and seeing how it flows before letting him cover it with gravel.

It may sound really picky, but trust me, if you don’t get it right at this stage, it will not drain well.

And this was a 2nd-generation excavator guy who did jobs for farms and construction sites all the time. However, he missed a few key points that home drainage experts all insist on – and slope is the first one.

3. Use Geotextile or Silt Cloth

Most drainage specialists go a few steps further than we did. They first lay geotextile or silt drainage cloth along the trench or culvert. They also cover the entire length of the pipe with a cloth sleeve of a similar fabric. The first video below shows you what happens inside your pipe if you don’t do this! Basically, I would have to re-do my pipe in a few years anyway, because we didn’t use any drainage cloth at all.

4. Extra Gravel & Wrap in Geotextile Cloth

Here’s another crucial step we missed (I figured all this out by watching hours and hours of tutorial videos after my project was completed): After you’ve dug your trench, you should first line the culvert with geotextile or silt drainage cloth along the bottom of the trench, with the fabric extending evenly up both sides.

Next, you put a 2 – 3-inch layer of river rock or 3/4-inch gravel on top of the geotextile cloth. Then you lay your wrapped pipe (in the sleeve) on top of that gravel and you completely cover the pipe with more river rock.

Lastly, you fold the geotextile cloth over top to seal off the whole package and lay more 3/4-inch gravel or river rock on top of the cloth. In a horse area, I would put at least 3 inches of river rock or 3/4-inch minus gravel on top of the pipe, and then another 2 inches of crusher dust on top of the gravel/river rock.

Personally, here’s what I will do next time:

  1. Dig properly sloped trench or culvert
  2. Line with geotextile cloth
  3. Pour 2 inches of river rock on top of the cloth
  4. Lay the hard-side sewer pipe, holes down, in the trench
  5. Cover pipe with river rock (sides and top) so there is 2 inches of river rock on top of the pipe
  6. Fold geotextile cloth, up the sides and over the top of the pipe so there is at least 4-5 inches of overlap
  7. Put 3 inches of 3/4-inch minus gravel on top of closed geotextile cloth
  8. Put 2 inches of crusher dust on top of 3/4-inch gravel

Note: You’re not going to want river rock as your top layer, because river rock is too big to drop through the tines of the manure fork and will make your poo-picking nasty.

5. Dig Your Trench Deep Enough

If you go through my ideal scenario above and add up the layers of gravel plus 4 inch pipe, I’m looking at 13 inches. So my culvert will need to be 13 inches deep at the highest (intake) point of my pipe and then get deeper from there. Using the calculation given in Step 1 to figure out the amount of slope, and adding that to my intake depth of 13 inches, means I would need to dig my culvert down to 19 inches at the exit and 13 inches at the intake.

6. Choose The Correct Pipe

YouTube has a number of good tutorials on how to lay drainage pipe, and for residential projects, most seem to use a flexible (corrugated) drainage pipe. But you would need to be really careful about the specs of the pipe you choose to make sure it can stand up to thousands of pounds of weight/pressure. Most of the drainage pipes are designed to be used in people’s yards, so they don’t have the weight-bearing capacity necessary for horse properties.

These are the two best videos of the dozens of drainage pipe installation videos I watched, so be sure and watch both of these before getting started on your own culvert drainage project!


Happy digging!

Jini Patel Thompson is a natural health writer and Freedomite. She began riding at age 2 in Kenya, and got her first horse at age 8 in Alberta, and so continues a life-long journey and love affair with these amazing creatures.

Adventures in Culvert Drainage for my Horse Paddock

One thought on “Adventures in Culvert Drainage for my Horse Paddock

  • March 29, 2017 at 5:29 pm

    Great journaling! thank you for the mention. Yes, I would have steered you immediately toward the filter fabric, and properly build drain. I would also advocate laying down heavier-grade geotextile fabric (more of a plastic mesh) down on top of compacted subgrade soils after removing the soft organics, and before placing the surfacing (crushed rock). That prevents it from getting churned in with the soil below and extends the life of the improvements.


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