/ DIY Bridge #111
So, I talked with a guy today, who does excavation, and he’s been building bridges (over creeks) with ‘retired’ flatbed trailers. The flatbeds are usually 48’ to 53’ long. In many cases he welds two trailer abreast so the crossing is 16’ wide. They also install buttress blocks, rip rap rock & gravel. He’s supposed to call me tonight to let me know when he can come & look at my situation. (Hasn’t called yet)
We’ll see what he has to say soon I hope.
I was hoping to find someone talk about this before I weighed in. This is all very true the calculations needed is called water delineation , it's where you find the amount of rain water that could flow in your area the short version of this it takes in a count for all the rain that washes in from the hills and mountains some places require you to a count for the big " 100 year storm" others need the: 200 year storm " that's why you see big culverts with a trickle running thru them .It is hard to estimate without knowing all the data necessary to do the calculation... in order to calculate you need to know the 100 years storm precipitation for your area, the stream basin area, the upstream volume and the flow of that volume... without these it is impossible to calculate... so if you don't know and won't find out then overkill it, perhaps have three pipe and have the road build as demonstrated below so if it's overflow it will flow on each side of the culvert on the road.
other than that, my opinion is most of the concrete work seems over kill.. thrench out 12 inch below the culvert grade and back fill with A gravel, compact, back fill the rest with A gravel and compact every foot... if you want a up stream and down stream concrete bulkhead fine but the rest is over kill.
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Is the picture you posted oriented with North on the Top?No Eyed Deer you certainly gave me some more to think about. Changing my driveway’s path, so it crosses perpendicular to creek/ water isn’t an option right now. My property is on the east side of the creek, the county road is on the west side of the creek & all I have is a 30’ easement. Neither neighbor wants to sell me an acre or two to change the driveway.
It’s been a real PITA to get anyone to give me an estimate on building a bridge. I do have a guy ready to clean up the creek bed and remove the piled up gravel on the side of the drive as soon as the water stops running. It’s down to a trickle now but we’re supposed to get somewhere between 2-8” of snow in the next 24 hours. Hopefully he’ll still be available after it melts and runs off.
I’ll probably make do with that until I can find some good (& affordable) bridge materials. I have about 25 acres of timber here. It’s not good timber but I could probably find enough trees to set them side by side until they’re wide enough to drive over.
Thanks for the thoughts & comments.
If you fill in the down stream side below the culvert with big rip rap (big enough that the max flow rate can't move them), that will alleviate the hole problem, no pun intended.Now that we're finally getting too much rain here in California all at once I'm glad I have a bridge with lots of clearance (8' high and 48'wide). My creek went from being ankle deep and 8' wide to up 5' deep and 35' wide on several occasions in the last month. As far as the idea of letting water over flow a hard surface or coming out of a culvert, I've seen what I call the "waterfall effect" where the running water scours out the downstream side of the discharge point eroding the creek bed when experiencing high flows. Often it may fill back up with silt when the fast flowing water subsides but often leaves of hole, or a pool, check out county culverts in your area. Also I've seen where the displaced material can create a sandbar barrier that further down that also alters the flow to one side or the other downstream. Whatever you decide, I like that quote from a movie of Morgan Freeman, " Go big or go home"!