Building a bridge in a flood plain?

[paintman161]

I want to build a bridge over a creek, it is about 40'-0" from edge to edge. Most of the year the creek is below the surrounding banks. But once maybe twice a year (depends on how much rain or snow melt) it does flood the surrounding areas but goes down within 2 days. I would like to make it 5' wide to drive an ATV across.

Is there any way to do this without having the bridge float away when the water floods the area?

thanks!

 

[SPYDERLK]

Any way you could create a small bridge on wheels that you could remove when threatened?

 

[Depmandog]

How high above the creek banks does the water rise during the flood events? Is the approach to the bridge location flat or could you build a XXX foot long bridge that would span the area that floods?

We need more info before we can give any decent answers. Keep this in mind, flowing water is mighty powerful. A 40' bridge is a healthy DIY project to start with. Adding on another major technical component (floating bridge, removable bridge, super long bridge, etc) will turn this into a major project. Not trying to dissuade you, just injecting a dose of reality.

Can we get some pictures or a site drawing to look at? From the bridge deck to the deepest part of the creek - how deep?

 

[paintman161]

no way to put it on wheels, the area is flat except where it goes up to the old railroad bed but that would be over 1000' bridge. The locations per google is: 43.300903,-77.844253 thats the approximate location i want the bridge as that would be on the edge of the property line.

 

[rd_macgregor]

A number of years ago, I built a 6' wide X 40' long footbridge across a (small) stream and flood plain. I bought steel square tubing and pounded it into the ground on each side of the stream channel and at intervals across the flood plain, then installed cross members and beams (all PT) with PT deck boards. It clears the stream by nearly 4' at normal flow and has 12 to 18" of clearance over the flood plain. It is mostly for foot traffic, but it has had ATV traffic as well. Now, I wish I had built it sturdy enough for my tractor to cross.

 

[ideburger]

Be aware of any permit requirements. I build bridges for a living and the US Army Corps of Engineers don't care much for unpermitted work in their jurisdiction. You should be ok with them if you stay above the ordinary high water mark.

When flooded, if the water velocity high? Bridges that end up under water are difficult to keep in place.

 

[bcp]

Build a bridge that can float, a strong, pivoting anchor on one end, and just a rest for the other end. Let a large flood swing it.

Bruce

 

[paintman161]

this is kind of what i was thinking, not sure the barrels would allow it to float or not though, may be too heavy?

 

[GLyford]

Just a thought here...

What's the bed of the stream like? Deep silt, or gravel? If it's relatively level gravel, how about building a concrete pad about 8' square, and 4' below your regular crossing height, with a veritical wall up to the road way height. On the other bank, put in a ramp that ends in another concrete pad, except now maybe just 6" to a foot below roadway height. You have basically just made a loading dock and a rest for the kingpin plate for a highway trailer.

Then get a used 40' flatbed trailer that will no longer pass road inspection. It already has the wheels and everything. Hook a chain to it and pull it across and out the ramp when foods threaten. Even if the floods take it away or wrap it around a tree, dig the debris off your concrete pads and buy another old flatbed trailer and you're back in business.

Even if the stream has a muddy bottom, you might be able to put in enough large rocks to make a stable enough bottom to wheel your trailer across when you need to.

 

[GLyford]

Another option: how about starting with a mobile home chassis? Leave at least one set of axles on it.

 

[paintman161]

Just a thought here...

What's the bed of the stream like? Deep silt, or gravel? If it's relatively level gravel, how about building a concrete pad about 8' square, and 4' below your regular crossing height, with a veritical wall up to the road way height. On the other bank, put in a ramp that ends in another concrete pad, except now maybe just 6" to a foot below roadway height. You have basically just made a loading dock and a rest for the kingpin plate for a highway trailer.

Then get a used 40' flatbed trailer that will no longer pass road inspection. It already has the wheels and everything. Hook a chain to it and pull it across and out the ramp when foods threaten. Even if the floods take it away or wrap it around a tree, dig the debris off your concrete pads and buy another old flatbed trailer and you're back in business.

Even if the stream has a muddy bottom, you might be able to put in enough large rocks to make a stable enough bottom to wheel your trailer across when you need to.

that sounds like a lot of money, plus i have not place to tow it out of the way, there are steep banks on either side of the creek (about 300' away) and too many trees to maneuver it around.

 

[Depmandog]

I used the GPS coordinates...not much help. I suggest if you want some quality ideas.....how about some pictures???????

 

[bcp]

Google aerial

 

[GLyford]

Hunh, and I thought I was giving you a low-cost option. Heck, there's even an add for a 37' camper for free in my local craigslist, you can't get much cheaper than an old trailer for structural bits. Even if you have to cut it apart and haul the rails through the woods one by one, then bolt the pieces parts back together once you get there you'd still be ahead for a starting point. Especially for anything close to 40'...that long a distance is going to set you back a good chunk of change. Price anything else against a couple grand for a used worn out semi trailer.

As to the concrete, I was thinking a durable base that wouldn't get washed away...but you could just as easily rest your trailer ends on gravel or rocks, anything you can get to where the bridge will be that will drain easily and not hold water against the frame to make ot rot or rust out. You might have to do a little more work getting it all back in position after flood before you set your bridge back on it.

One way to make a sort of concrete bulkhead for either end of your bridge is to just stack up bags of concrete, paper and all, like bricks. Then drive rebar down through them to hold them in place in a few spots. The rain and ground water will get into the bags and set them over time. There's a couple other posts on TBN here somewhere where people have done this for the ends of a culvert and such.

So, in addition to the stream itself, access to the site seems to be an issue for you. Anything else?

 

[Depmandog]

Google aerial

. I was thinking boots on the ground, using the old camera and taking a few pictures, but hey...it might be just me that's having a problem visualizing the best bridge design.

 

[paintman161]

. I was thinking boots on the ground, using the old camera and taking a few pictures, but hey...it might be just me that's having a problem visualizing the best bridge design.

well this is at my property which is 30 miles away, I am hoping to be up there this weekend, but that depends on if we are going to get hit with another snow storm.

 

[Josh Shoemaker]

Just get permission from the neighbor that is just to the right of where you are at. There is a bridge just to the right of where the property is.

 

[paintman161]

I can get the bridge over there and down into the spot but Once i get the bridge down in the bottom I wont be able to get it back up. Its kind of like a large bowl in there.

 

[MotorSeven]

My creek is 35' bank to bank and the banks are almost 8' high. Seasonal flooding(winter) will see water over the banks in the place I built the bridge up to a foot. I used a 80' mobile home frame, and welded it in three sections so it looks like an open "U" which raised the main section of the span about 5' above the max flood stage. At each end I poured a concrete footer and bolted the frame to it, then made the approach out of gravel so it could be replaced if the water got that high and swept the gravel away.

I have not driven a wheeler on it yet because I have not reinforced it yet and I am pretty sure it would collapse. It needs two power poles sunk at each end and the sides of the bridge lagged or bolted to them. Then a cable run from a ground anchor up and over the tops of the poles across at about waist high with connecting cables running down to the bridge every 10' or so. Once this gets done I would have no problem driving a wheeler across. Some pic's:

 

[MotorSeven]