Questions on installing a culvert on my land

[chesterspal]

I'll add that a single pipe of larger diameter is going to carry more flood water than 2 smaller pipes, side by side.  Buy a single 30" pipe or even a 24" pipe.  Position it correctly (need to prepare a good bed so the pipe is on a good surface).  Like chesterspal say, it helps to compact the material around the culvert.  I also agree with him on the double wall HDPE pipe vs metal.  Stronger, better flow, won't rust.  Keep the ends covered with rock or wood to keep sunlight off the ends.

Correct. It works out to be 4 times the water.
So, a 30" diameter pipe will carry four times the flow as one 15" in diameter.

I'd go with two 15" side by side since I cannot backfill anything much larger. Remember, I have only a 30" deep opening to work with. I must back fill 12" on top of that 15" pipe or it will crush under the weight of my truck. So, that gives me only a 3" margin of error, so to speak, atop the culvert for back filling.

Another factor for not going with the bridge is...
Unless it is raised much higher than the water channel it can be washed out during one of these 100 year floods that seem to happen every 5 to 10 years now. That gets into constructing pillars sunk into the ground with concrete bases and that whole "frost line" deal someone on this site elluded to. Plus the ramps that will be needed on each side to get on and off the bridge with that 6000 pound truck.

Frankly, it seems way overkill for what I have here. 

With the dual culvert, the water will likely just run up and over and down the other side. If the stream this channel dumps its water in to is down hill, (and it is) it will still end up there.



There will be some erosion of the soil around the culvert pipes but that can easily be repacked after the rain subsides.

[RetiredTech]

  I'll throw out another option. If this trench is on your own land and only used by you it may be more cost effective to dig out an entrance and exit slope you can drive through. Sink a couple treated timbers in the ground at the level of the bottom of the trench then plank over it with 3" or better tread to drive across. They used these low water bridges down here for many years down here to get across creeks and dry branches where there wasn't enough traffic to warrant a bridge. It doesn't sound like water volume would ever prevent you from crossing and most of your debris will flow right past.

[Ron Scott]

https://forestryforum.com/board/index.php?topic=9011.0

[Magicman]

I must back fill 12" on top of that 15" pipe or it will crush under the weight of my truck.

Just as important as proper top fill or maybe more so is your side supporting fill.  If the culvert can not squish out, then it can not squish down.



 I dig down and bury all of my bridge stringers below ground level, shown here while replacing a broken decking board.


 That makes my approaches level.  My bridges routinely get 2'-4' under after heavy rains and I am not concerned about wash out.  This is my longest bridge @ about 15' span.  The shortest one is about half of the above.

[Ianab]

Seen all sorts of things done over the years, most of them worked.

Thing that most people underestimate is how much higher that 4" of water can get occasionally. Stream in my back garden looks a lot like that, but the water has also been lapping at our footbridge ~4ft above the normal level. If goes under the street about 50 yards downstream, through a ~4ft pipe.  We are in a high rainfall area, but even drier places can get freak dumps from a thunderstorm etc. 

If I was doing 2 smaller pipes, which will probably handle the flow 99.99% of the time, I'd also design it to overflow with minimal damage. So a couple of utility poles on each side of the culvert, and a good rock layer between them. The poles should help hold things together if the culvert overflows. 

Precast concrete culvert pipes are still a thing here too, although plastic has become more common due to being easier to handle. But you can still buy the concrete ones  in ~10" to 9ft dia. 

Main thing from the environmental point is that you don't disrupts the fish movements. So things like weirs and pipes that discharge 3ft in the air are no-nos. A sensible culvert / ford or bridge may or may not need a permit, but if you don't mess with the fish, it's much better.

[BaldBob]

If you cannot put in large enough culvert to handle major flood events ( e.g.. if a 36" culvert is needed , 2 15" culverts won't meet the need ), It is is a good idea to put in an armored overflow near the culvert location to prevent culvert washout or other expensive repairs. This is simply a rocked dip near the culvert.
                                                 

         roadbed    --------------------u--- armored dip (ignore parts above road bed in this illustration)                                                      
                                 culvert  O    

[doc henderson]

Chesterspal, overkill is what we do best.  you did ask.  You do what works for you.  I doubt aliens will come and take your bridge out with a laser beam, but we can plan for that.  Lots of good knowledge.  you could start with pressure treated railroad ties or tele pole parallel to the stream, with oak or similar thick planks on top going across the stream.  build up rock and dirt as an approach.  if it flexes, add thicker or more planks.  if the bridge washes out every 10 years, build another, with maybe add more detail listed in the prev. responses.  We all know that if the truck is ok, then someone will pull a loaded trailer across it at some point.  Or go with culvert pipe and see how it goes.  I have found 6-foot scraps at city yards they gave me for free.  although it was for fixing a problem at a scout camp.  I also got some free from and elevator that used plastic culvert to ventilate the piles of wheat on the ground.  got them for free.  Do your thing and send some pics.  



 

 

[doc henderson]

have fun.

[peakbagger]

Some folks in areas with spring run off issues attach a steel cable to the uphill end of the culvert and wrap it around a tree. They do the same with bridges on occasion, when the spring flood comes it is easier to rebuild if the culvert pipes and bridge beams do not have to be fished out of the woods a few hundred feet down. I was at spot this spring where the main beam for hiking bridge was about 300 feet down stream. 

[chesterspal]

Seen all sorts of things done over the years, most of them worked...

Main thing from the environmental point is that you don't disrupts the fish movements. So things like weirs and pipes that discharge 3ft in the air are no-nos. A sensible culvert / ford or bridge may or may not need a permit, but if you don't mess with the fish, it's much better.

No fish will be harmed in the making of this culvert.
It's a runoff from down the hill.

[chesterspal]

If you cannot put in large enough culvert to handle major flood events ( e.g.. if a 36" culvert is needed , 2 15" culverts won't meet the need ), It is is a good idea to put in an armored overflow near the culvert location to prevent culvert washout or other expensive repairs. This is simply a rocked dip near the culvert.                                              

I don't know what (largest) size might be needed... but my plan at this point is to take another look in the Spring when the thaw run off is the greatest. 
At least then I can size the pipe for what is needed most of the time.

[chesterspal]

 I'll throw out another option. Sink a couple treated timbers in the ground at the level of the bottom of the trench then plank over it with 3" or better tread to drive across...

Intersting concept. Not sure it will work in my case. 
Might turn into a muddy mess.

[PoginyHill]

Have you considered a ford crossing? If the approaches to the stream-bed will support, you could fill in the crossing with large stone (6-8") enough to drive across (maybe top with 1-1/2 stone to prevent possibility of popping a tire). Normal flow would probably go through the rocks. Heavier flow will go on top of the rock, but should stay put. The wider you can create the bed for heavier flow, the better. I have such a ford on one of my woods roads and it works very well. This is a perennial stream that has significant flow at times. I had three 15" culverts. The ford works better.

[Treeflea24]

If the stream/creek is big enough, or drains a large enough area, it may show up in the USGS's StreamStats tool. Heres a link: StreamStats
Once you zoom into your area, if you see a blue line representing your creek, you can select a point on the line and the program will show you the basin that it drains, the peak flow rates for certain flood events (50 yr, 100yr, etc), slopes, drain area, etc. We have a seasonal creek here that is dry or just patches of puddles for 3 months of the year, and it shows up on the tool, so your little stream may too.
If/when you get the flow rates for flood events you could then size the culvert(s) with some more confidence that they wont be overtopped by a whatever-year flood event.

[Magicman]

Thanks for that link.   

[Machinebuilder]

That's an interesting link

I can select a dry gully that only has water if a hurricane or similar comes through.
When it does have water much of it comes from wet weather springs

[stavebuyer]

Ford. Anything you put in the bottom of the channel that is below the original stream bed tends to stay put. Low bridges and inadequate  culverts never last.

[RPF2509]

I agree with stave buyer.  I've seen many failed undersized culverts.  Double culverts are designed to clog.  Go big or try a squashie (an oval culvert).  I think they are only available in metal.  Do a watershed drainage calculation to find the most appropriate size.  One big storm will wash out all your savings by going undersized.  Bridges are best and short spans are relatively cheap.

[RPF2509]

A rocked ford should also be on the consider list especially if you dont use the crossing much.  Very cheap to put in and self maintaining.  Be sure to rock the approaches as well.

[dougtrr2]

Probably cost prohibitive, but concrete culvert can be round, arched, oval, and boxed shaped.

Doug in SW IA

[tbeforester]

Instead of using a culvert to cross your stream, would a ford crossing work? Sometimes they are more reliable than a culvert giving that your only using it on occasion. Plus on our company properties, maintaining culverts can be a hassle especially after heavy rains. Culverts are more prone to blowouts and clogging up. Fords will usually allow debris to pass on by. Occasionally you will have to go back on a ford and touch them up. Just depends on how much time and effort you want to spend on them.

[PoginyHill]

A look at the culverts and ford on my woods roads during Vermont's "flood" this week.
Damage was pretty minimal for me.

Vermont's Dec 2023 Flood - YouTube

[doc henderson]

nice documentation relative to this question.  stay dry.

[aigheadish]

For better or worse, I've done what OP is asking about. My creek, which has been dry almost this entire year, will occasionally flood pretty significantly. It started with a rock ford as mentioned but I had trouble crossing it with my small mower and it did have a small concrete culvert buried in it.



 

Upon the first flood we had after we moved in the flood waters would spread 50+ feet away from the creek, across my relatively flat back yard. We had more culvert, but really garbage PVC stuff, so I dug up the rocks and concrete culvert, and reburied everything, with mostly rock or chunks of concrete on top. This ended up being 3 pipes, each maybe 12-16" in diameter, but they were also only 12-15 feet long which meant after another good flood a fair amount of the material washed away and the bridge became only wide enough to drive a truck over and it was sketchy. I need to get the backhoe over, which I did a couple times but hated every second of it. Next, I bought two 24" HDPE culverts that are 20' long. I dug everything else up, including a big chunk of material before where the culverts are going and laid the 2 pipes in there with rocks and dirt packed in between them maybe a couple feet or so wide. We've then added more rocks and dirt to the top and I put some screening material over the entrances of the pipes to hopefully keep crap from getting in there. I can backhoe out any material that may get stuck pretty easily. So far, it has gone untested, over the past several months. I am a bit concerned that the material in between the pipes washes out but we'll see what happens.

My initial plan was to bury some gabion baskets full of rocks and place the culverts on either side, so the center washout wasn't likely to happen, but the wife got sick of seeing the culverts laying in the yard and said "if it washes out we'll just fix it" for now it's done and she's right, but again, we'll see.



 

[aigheadish]

Welp, we had our first good rain today, to test out the culverts. I didn't get a picture of the culverts themselves but they worked. The screens are likely a bad idea. They are getting clogged, pretty easily, with very small sticks and leaves, even though I think it's a 2"x2" opening. I'll probably take them off. No water over the top of the bridge. No apparent degradation of the material holding them in place (I know this is the first and only good rain so far).

This is the area right before the culverts. Holding a lot of water but again no flow over the bridge. The culverts are probably about 3/4 full at this point.





We also lost a dead standing ash in the process that took out the trampoline. Lost at the roots not broken. It looks like it'd provide some nice lumber.