DIY Bridge

   / DIY Bridge #11  
If the upstream creek runs thru a wooded area, it's just a matter of time until culverts are blocked by sticks, then leaves, during a gully-washer.
 
   / DIY Bridge #13  
FWIW, creek beds usually wash out to a size that naturally handles the flow of water including seasonally heavy flows. I'd be very cautious about putting anything into a creek bed that obstructs the natural channel because one has to assume that the creek bed is the size it is because of the water flowing through it over time.
 
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  • Thread Starter
#15  
Over time, it seems to me that culverts concentrate the flow of water when there's a lot of it. This can erode the stream bed downstream and/or erode the banks downstream.

It also seems like it is too easy to undersize culverts, either by underestimating the volume of seasonal water flows or by getting surprised by those occasional gully washing rainfalls.

I have no skill at estimating water volume and culvert sizes myself.

The last one of these that got built nearby seemed to have intentionally been built with a dip in the middle to allow any excess water to run over the top of it.
I have a fry creek that runs across my driveway. After heavy rains the water runs through & will get up to 3-4’ deep and might run 60-70’ wide. I want to hire a dozer to come and clean the creek bed up (push gravel to the banks and straighten the run a bit. After that I would like to install two 36” HDPE culvert pipes. The plan is to trench out a footing on the upstream side 24” deep under the culverts, pour concrete in the trench, pour 12” of concrete on each side of the culverts as well as between them. Use 3/4” minus to fill any voids in the driveway and ‘level’ it out. After that I’ll pour a 6” concrete slab on top with #3 rebar 12”OC. The upstream side would be concrete (to keep the water from getting under the bridge) & footings would be on each end of the slab. This is the only access I have to my house & property and it would need to be able to stand up to occasional heavy traffic. ( concrete trucks, logging trucks, triple axle trailers & such) Will in work? Am I going overboard, do I need more ‘fill’ over the culvert. TIA for your help.I will try and post an example of the bridge I thinking of.
garymartin63965
That should have said dry creek.
 
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  • Thread Starter
#16  
Over time, it seems to me that culverts concentrate the flow of water when there's a lot of it. This can erode the stream bed downstream and/or erode the banks downstream.

It also seems like it is too easy to undersize culverts, either by underestimating the volume of seasonal water flows or by getting surprised by those occasional gully washing rainfalls.

I have no skill at estimating water volume and culvert sizes myself.

The last one of these that got built nearby seemed to have intentionally been built with a dip in the middle to allow any excess water to run over the top of it.
Would like to build it to function as a low water crossing (after a heavy storm/rain with water washing over the slab) with the hopes I would be able to cross it sooner. Have not read all replies yet but many are saying the downstream side of the slab will probably need the same amount of concrete to keep things from washing out whenever water spills over the slab.
 
   / DIY Bridge
  • Thread Starter
#17  
I’m not a storm water engineer but your described flow of 4ft deep or even 1 ft deep 60 foot wide is drastically more than 2 36” culverts could handle. For a volume of water that large I think an actual bridge would be better. Assuming the 70 foot wide is a typo and you meant 70 inches that’s still too much water to fit through those culverts.
70 ft is a safe estimate. Here’s a photo of it when it’s up. It’s almost 100 wide at this point. So I’ll need to make sure my bridge will work as a spillway at these times. Thanks for your comments.
 

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   / DIY Bridge #18  
It also depends on how strong the flow is. If it is largely standing water or very slow moving then your idea may be alright. If there is flow and it increases a fair bit after it rains then you will have erosion issues to deal with.
 
   / DIY Bridge #19  
Others have used sem-trailers in bridge costruction. Not sure if that would meet your specs.
 
   / DIY Bridge #20  
Oops.. Posted the above reply before seeing the picture.. You definitely have a fair bit of flow there.
 
 
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