Hey all – my bridge washed out 2 or so times per year. I usually just push the gravel back on top and move on with my life. But it happened last night. When it floods, the gravel washes away and exposes rip rap sized boulders.
I'm wondering: I'm thinking about piling the rip rap higher by hand about 1 inch from the top of bridge and then pouring some dry concrete over certain areas to lock in some of the smaller pieces and THEN gravel over.
The thinking is that next time, there will less wash out (only the 1-2 inches of gravel rather than the smaller rocks/rip rap).
Wanted to stress test that idea with you all, especially the concrete dry pour concept.
by mollysdad61
26 Comments
Hire a professional. There seems to be a lot going on here.
Id concrete the entire thing. I don’t think dry pour would hold up.
You’ll never win by trying to out muscle the water. Gotta work with it
Be careful, this may not be legal in your state. WA for example has strict laws about bank hardening, when it is allowed and when it is not. You might want to consult with a professional, just to confirm what your proposing is legal.
I don’t think you’ve got a bad idea, but I think layers of gravel in between the rip rap before a cap of dry pour would help further isolate the movement and impede the water flow that is causing the issue
Fyi I’ve already talked to 3-4 engineers and companies. Permanent fix isn’t feasible from cost perspective. Just looking to improve my band aid.
I’m in municipal road construction and have some experience with this type of flooding.
I’d first check the entire length of the damaged area both sides that there’s no deep pockets of silt, mud, very small stone or weird air pockets covered by debris and that instead it’s all indeed solid big rip-rap.
Whether you ultimately cap with concrete or as I’ve seen done more frequently, blacktop, be sure to take it down both sides to toe of slope and tuck in edge under massive flattish boulders that maybe you’ll need a trackhoe excavator coming in from the sides to place. This will prevent flood waters approaching from the upstream side from getting under, forcing upwards and peeling/rolling it up and over AND protecting it on the downstream side from flowing over the edge, curling under and scouring out, collapsing pieces off.
Also seal all seams well where it meets bridge deck, abutments, and wing walls and inspect periodically that seals are intact. Preventing floodwater from working on getting into weak spots is key.
Making the bridge structure and it’s roadway approaches as easy for the water to flow around and over as effortlessly as possible with as little “drag” as possible is what you’re looking for.
Finally not sure if guiderails or at least sturdy delineators wouldn’t be a good idea on both the bridge deck and approach inclines.
Edit: as others have said, check with a professional knowledgeable in your area’s hydrology, state’s engineering and environmental permitting requirements to make sure you’re doing it right. What works in one place might not in another jurisdiction.
I would think gravel on top of concrete would wash away even easier. It should be boulders then gravel then concrete. Dry pack concrete really isn’t that strong either and would probably wash out just as easy as the gravel as well as contaminate the water until it hardens.
I wonder if there might be government grants for situations like these. Isn’t this usually under the army corps of engineers?
If you want to avoid washout, you need to excavate, put in some big ass culvert pipe on either side, and then backfill properly and then pour cement to hold everything in place.
Just pouring a cement cap on either side is not going to do a lick of good, as any water will erode under it, make it rock and break, then you have sharp concrete to threaten your tires.
You also shouldn’t be so cavalier about where you live and regulations around streams and watercourses. “Wild West” isn’t a good enough answer. States and the feds do studies around watercourses, and if you do something illegal the fines can be astronomical.
Unfortunately, unless you raise the bottom of the bridge, there will never be enough capacity beneath the bridge to let the water through. Of you keep building the top of the bridge higher, the water will just stage up until it finds a way around the bridge. The it will erode something further up the road. You also run the risk of the water level / pressure being so high that it pushes the bridge off of the pilings which would be considerably worse. There is way too much momentum in a quick stream to fight. You have to either get out of its way or just deal with the consequences.
I’m sure replacing the bridge isn’t feasible. So, the only other thing I can think of is digging a secondary channel into the woods through some large culverts; which is still considerably expensive. OR trying to partially dam the stream upstream of the bridge which will turn your property into a floodplain.
But there isn’t a solution that won’t require a professional engineer because you’ll be changing the hydrology and affecting your neighbors water rights.
I’m sure this isn’t the solution you wanted to hear. But, I think you’re kind of stuck. The only real solution is to build the road so the bottom of the deck is out of harms way. The only feasible “cheap” solution is to get rubble rip brought in to build it up and layer smaller and smaller aggregate on top until you get a surface you can drive on. Even then, you’ll risk wash out.
Stop with the dry pour nonsense. The instructions are on the bag. Follow them. The only exception I’m aware of is leaving the bag in place to harden as in sand bags or retaining walls.
You probably already know this but if it’s washing out this regularly the the bridge is undersized.
You don’t want to replace it with a larger once cause that’s expensive. Ok let’s find a way to work WITH the water.
Raising the road bed won’t work cause it will still just overtop. The higher it is the more will wash out.
If you have some equipment, I’d think about trying dig out a lower swale that goes around the bridge. The further away from the bridge you can make it the better so that you can have gentle gradients. This will serve as a flood channel to divert the water at high flows. Make it wide and shallow rather than narrow and deep. Establish some well-rooted grasses to hold the ground. In the field to either side of the road. Keep your road bed as flush with ground height as you can. If the road doesn’t protrude it will erode less.
On either end of the bridge you could concrete the driveway a short slope away from the bridge until it gets down to flush with the surrounding ground and then gravel from there.
Also if you have a bit of time and elbow grease you can cobblestone the drive where it washes out. Get some rocks at least 4″ diameter up to however large you can handle. Dig out and pack them in close together, preferably standing on end so they support each other side to side better, but a flat side up to drive over. Pack the cracks with sand and gravel to cement in place. After a rainstorm or two to wash it in, re-sand it.
Why dry pour? Seems like regular wet concrete makes more sense to make sure it’s strong. You obviously have water available…
No need to dry pour when you’ve got plenty of water available under the bridge. Bucket on a rope if you have to lol. In all seriousness though, I agree with the others saying to add gravel first, then concrete cap, and digging a very healthy flood overflow channel and culvert (across the lower side of the road, assuming the banks are uneven). When the water rises, you want it to start draining into the channel, under your road you through the culvert, and out the other side of the road back into the creek.
Place more or bigger pipes under the bridge to lessen the obstruction of the bridge in the water. Next seal the bridge in clay or better cement with iron strengthening in it.
Not a professional but used to do some landscaping. Would polymeric sand work well here as it’s meant to be dry poured and then watered?
It’d be better to create an overflow spillway across a low point in the driveway with maybe geotextile fabric. I’ve seen way too many concrete fixes that just wash out underneath. Not to mention concrete fixes are ugly. The water will speed up causing more erosion someplace else that may make life even worse.
How much of the watershed of this stream do you own? There are tactics you can use to slow water down to reduce flooding.
The fact that the surrounding area is so bare probably isn’t helping. Look into what trees/deep rooted shrubs grow well in rocky/sandy, moist conditions in your area, plant a bunch of those. Add some organic matter if you have to while the roots are getting established. It won’t solve the whole problem but could help reduce erosion somewhat/help improve your bandaid.
Adding concrete will just shift the problem to the new edge of concrete.
Please don’t do that. When dealing with water we want to slow it and infiltrate it. By putting concrete you’re making an impermeable layer that will cause more runoff and more downstream issues. I would try somehow vegetating the flood bank upstream of the issue as much as you can for water to be slowed when it does flood.
There’s a great channel on YouTube called “Water stories” that explains the drought flood cycle. That is your true enemy. By healing your portion of the watershed, you stand a better chance of being successful in the long run.
Ya dry pouring concrete is never a good solution. If you paying for the concrete at least mix it and do it right. A break water is probably a good idea
It will scour quickly and cause failure
“Rip rap”?
One other clarification. My idea is more so to use concrete in some for the cracks to tie some of the rip rap together. Not to actually using dry pour as a surface for the driveway. More so filling the gaps with it instead of filling it with gravel. So that 4-7 pieces of smaller rip rap get tied together and make 1 larger boulder, effectively.
You don’t have a water problem, you have an ENERGY problem and the more you hold that water back with obstacles, the worse your problem gets. Real risk that hardening the banks will lead to the water scouring out the dirt under your bridge foundations. Instead I’d focus on moving the water more efficiently
If I were someone willing to do this illegally without permits, I’d rent an excavator and deepen that channel. Basically make the center of the stream a foot or two deeper for about 100 ft in front of, and under the bridge.
And while you’ve got the excavator, dig out that riprap and put in a steel culvert, then replace the riprap.
But all of this carries risk of unintended consequences– give serious thought to what is downstream that could be damaged by the now-accelerated flow. It may be the wild west but that doesn’t insulate you from lawsuits that’ll run you way more than the 60-100k you’re trying to avoid.