Building a bridge in a flood plain?

Kapnfriday · Dec 27, 2013

I follow you, but I don't think I'm going to try that. My poles are pushing 25-30 feet long and 11 inches in diameter at the thick end. Plus I don't have a BH to weigh down the rear. I lifted 3 8' RR ties in the FEL and got that light in the A feeling you mentioned.

My span is about 18 feet, but I don't want to cut the poles to length before getting them across - I might need that extra length to get the pole out over the bank without it tipping into the creek.

MotorSeven · Dec 28, 2013

Kap, I left it "on the ground "horns up" as it is in the transport picture and set it on the bank where I wanted it. I then put a pulley on a tree across the creek and attached a cable from the bridge thru the pulley and to the back of the tractor. I used some long 4x4's on the pulley side and angled them down into the creek to catch the end of the bridge as it came across and deflect it up over the other side. All of that went pretty much as planned. What did not go as planned was when I tried to roll the bridge over to get it in the proper "horns down" position. Rolling 40' of light steel from one end didn't work and the whole thing twisted like a pretzle. I had to pull it back across into the pasture, use the FEL w/ forks to straighten it back out, then bring my 25KW pto generator and 230amp welder to the location. I had to re-weld several broken welds, then reinforce the bridge in a few places, then drug it back across for another try. This time it held although is still has a slight sweeping bend to the whole thing.

So if you have to flip one, get another tractor on the other side and flip from both ends at the same time....it will save you some grief. For your application, I would build the whole thing including the decking, then winch it across in final rest position. If you get the winch up high enough in the tree, it will help keep the end from digging into the bank as it comes across. If you push with your tractor while someone winches it will be much easier and go a lot faster with less stress on the cable & come-along.

Leejohn · Dec 28, 2013

Rig up a zip line, hook end to it and then just push it over to the other side.

paintman161 · Dec 28, 2013

Here is some pictures of the creek, when it does flood it goes over the banks and i would guess at least 24" above the banks but this really depends on how much rain we get. First pic shows the down stream, second is up stream, third is one possible location for bridge, last is another possible location.

Tractor Seabee · Dec 28, 2013

Answer the questions we have all asked and you will get some more and hopefully better ideas. Looks like there are plenty of trees to use to drag an assembled bridge across from one side. If dollars are a constraint then a ready made platform like a truck bed is your cheapest way to go. New materials are nice but add up real fast. Hard to visualize from your pictures what the 2' above the bank a flood will do with sills and approaches on each end. Speed of the water flow is the key element there. Can you get a contour map of the area? That will give a clue to how the flood water spreads out on each side. The bigger the spread probably the lower the water velocity. Fast moving water is very destructive and can put a lot of pressure on the sides of a bridge when compounded with the negative pressure created on the downstream side. A lot of engineering goes into building bridges.

Ron

bcp · Dec 28, 2013

Contours:

Bruce

Tractor Seabee · Dec 28, 2013

Great, now mark where you plan to put the bridge. Best place is where the contour lines are close together as that is where the water will spread out the least on each side and you do not need to elevate to clear flood water under the bridge; but that is also where the flood velocity will be the greatest. What is the spacing of the contour lines? Standard is 2' and 5' depending on where the map is from.

Ron