View Full Version : Culverts: how best to avoid washing out in the spring run-off?

Apr. 19, 2011, 06:57 PM
We have a couple of culverts on the farm for a ditch that becomes a minor raging torrent in the spring.

This being a particularly wet spring, with some heavy 24-hour downpours, one in particularly is almost completely washed out, with a mini-ditch about 18" deep down each side of it. It had washed out underneath first, I think, and then the top broke broke through once it thawed.

They were re-set by a contractor with a dozer a couple of summers ago, but they'll need doing again, probably.

In the meantime, for future reference, what's the best way to avoid the washing-out effect ? They're just packed with whatever ground was close by, so a mix of clay, soil, sand, small rocks, gravel, etc.....none of which has remained.

I thought about setting some big flat slab rocks (and old 18" paving stones that we aren't using) vertically at the upstream sides of the culvert to try and alleviate the power of the water...any other suggestions?


Apr. 19, 2011, 08:17 PM
I think that you may need to size them larger. Ours is 20 or 24 inches and we don't even have a ditch, just a swale that fills up fast during thunderstorms and then it starts meandering across the road.There's a guy down the road from us with a pond and he has lost the dam twice because his spillway culvert is too small and higher than the lowest part of his dam. It's not even 300 feet away from the road and is scaring me to drive past it.

If your dozer guy knew it had been washed out he should have suggested changing the size or offered to reinforce the sidewalls of the ditch too. If you have the big rocks I'd use them, just make sure they are angled just so or they might make a hole elsewhere.

Apr. 19, 2011, 08:39 PM
Well if possible, you may want to put in a bigger tube, which will allow the water to run faster and not slow it down AT ALL.

We also have a ditch, which is the bottom of the local runoff for probably a mile around. That water can get very strong when there has been a steady rain for a couple days, spring and fall seasons. You can literally watch the water rise and fall as the runoff drains past our house.

Since the ditch drains under the driveway to the barn, used to run thru the back yard, I got VERY well acquainted with the oddities of ditch drainage over the years.

When we "improved" the driveway to the barn, we dug out the old culvert, which included 4 pieces of 12" inside hole, cement tubes. We had a 24" inside dimension one-piece metal tube put in, filled over it. Have to say that has made an IMMENSE improvement with the draining times. We also had dealt with the water digging out the tube ends, so I had son take a bunch of our cobblestone rock and place it around the tube, covered the rocks with left over cement from another job. So now tube has a cement approach lip and wide edge on both sides. All the approach is about 2-3 ft wide, cement thickeness tapered out to make it easy for water to slide in.

We don't get the tube washout now, nor puddles around the end of water that couldn't get inside.

We did make a project one fall, laid more 24" inside dimension, cement tube in the length of ditch on our property, also across the neighbors back yard, and then covered the whole length of ditch. Neighbor had connections, got the dirt free! Locally there is a cement factory that makes "products" like cement tube. They will GIVE AWAY tube that doesn't meet DOT specs for highway work. They will load your trailer, but you haul away and deal with it at home. At the time we had a backhoe, so no issue for us.

We have had the covered ditch about 10 years now, and it REALLY deals with the water for us. Kind of like a sluice, power of the water keeps the tube cleaned out, scrubbed, in heavy rains. We have much better drainage now with the tube, water comes and goes pretty fast unless volume is huge (more than several inches in a couple hours), which does happen at times. Then the water will back up across the road, in the neighbors yard, which is unused. So the water just runs off slower then, if our open ditch before the driveway tube, is full.

I make a SERIOUS effort to keep the open ditch area well mowed with the weed whacker, no bushes or trees growing in the open ditch. Banked walls are steep, all of which helps water drainage to run off quickly, NOT slowed down in passing. The water coming out of the tube under the road from neighbor has a cattail bed to soften the water force. USED to be like a hydralic hose, just washed out my ditch bank, undermining fenceposts. Water seems to move quickly thru the cattails in a 90degree turn, to enter my cleaned out ditch and run off.

In an effort to "keep the tube clean", I did put a grate over our tube opening, to catch sticks, leaves and floaters going down the ditch. The effort of water to get thru the grate slows the flow about 2/3s. This is a large grate, with metal slats vertical, inch width open full length between slats. Water can run AROUND the sides of grate, not closed off by the grate. I was just looking to catch direct flowing items. With the grate in place over the tube end, I can precipitate a flood upstream, since water can't run off fast enough now with tube blockage.

So doing a cement lip around your tubes, will help with washouts. I strongly suggest changing to a bigger tube than you now have, if you are going to put in any work. The plastic ones are now available, will not degrade over the years, can hold a lot of weight. I really wish we could have put in 36" inside dimension tubing thru the yard. I don't think we would ever flood if we had.

Maybe using your slab rocks as lip edging, until you can get cement in place, could help. Perhaps the slab rock WITH cement between would make a good edging. Adding BIG rocks around the lip edges, some in the cement, with a bigger, amount of rock on the down hill, draining side, should help too. Bigger rocks, maybe rocks over geotextile fabric under to hold dirt in place, will be harder to move with the water forces. You are trying to prevent water reaching the dirt particles and wash them away from rocks and tube with the cement between rocks.

I seriously would NOT recommend blocking water entrance to tube at all, water will back up on you, causing other, perhaps more severe, problems.

Tamara in TN
Apr. 19, 2011, 09:01 PM
I think that you may need to size them larger. .


washing "normally" means a bigger culvert it required....do you need to do a 100 year culvert no? but washing every year means changes are in order


Apr. 20, 2011, 09:09 AM
Oh, and wait until the water has subsided to try to lay a new pipe. It just doesn't work when the water's rushing under it! Ask me how I know that.....

We did a lot of culvert work ourselves a few years ago and the tubes are anchored at each end with concrete forms AND rocks. Make sure the face is wide enough to funnel the water into the tube, which does have to be big enough to not slow the flow. Of course since that spring we haven't had quite the same flooding but neither have we had any washouts.

Apr. 20, 2011, 10:54 AM
They're just packed with whatever ground was close by, so a mix of clay, soil, sand, small rocks, gravel, etc.....none of which has remained.

Instead of using the above, which will readily wash away, you might want to talk to your excavator about using riprap, (http://en.wikipedia.org/wiki/Riprap). Its size and irregular shape tends to stay put, and what water does get through won't be a raging current to further erode the sides of the culvert. It's works well to stabilize the sides of waterways.