# Small creek bridge that can wash out



## chris_evans

I have a small creek that I would like to construct an 8 foot bridge across. However, with bad storms, the creek swells. In hurricane type storms, some of the bank has eroded.

I would like to make a bridge that can 'washout' and a small wall on the house side to stop erosion.

My question is, what kind of mechanism can take that weight? It just needs to hold the bridge. I looked at stainless steel swivels with bearings, but I think I need something else. It doesn't have to be fancy, I was thinking about two large pieces of pipe one that fits over the other.

Any ideas? Anyone seen anything like this? I was unable to find anything online.


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## nealtw

Welcome to the site, interesting idea.
Just a few thoughts. I would move the pivot to one side and plant a pole on the middle of the so you can run a cable  down to the other end of bridge to carry the weight of the bridge and then two anchor cables down behind it to add support to the post thru both locations. Two greased pipes for the bearing might work, you could also put three casters under it.


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## Chris

Pedestrian only bride I assume?


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## nealtw

Chris said:


> Pedestrian only bride I assume?



Did you make your bride walk?:trophy:


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## Chris

You know it. Stupid auto correct.


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## beachguy005

If you're going to be building a cantilevered walk, instead of being too concerned with a bearing I would just have a counter-weight on the opposite and let it pivot on a piece of pipe set in concrete.
If the section over the water weighs 200 lbs., attach 200 lbs. under the landward side if permanent , or on top as temporary just to move it.
You could also install a homemade cable suspension bridge.  A web search will give you quite a few ideas on that type.


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## Mastercarpenty

Better begin with making sure you can legally alter the creek-bank and seeing which agencies you'll have to get permission from. Almost every riparian area in the US now falls under Federal control (Corps of Engineers) and the permission process could easily take years if your local staff is hesitant to deal with it. When you alter water's natural path you become legally responsible for any problems that causes downstream, and while I don't see any related issues with your idea I'm not qualified to say there are none. 

If you have machine or muscle power enough, an alternative could be to chain or cable one end uphill to a post or tree, then reset the bridge after-the-fact. The chain or cable could be slightly buried normally for aesthetics. Not a lot of trouble for a 5 year event but if it floods out more often that could get bothersome. 

You could also create a drawbridge and winch it up when flooding looms. Again a handy tree might provide the winching anchor. You could even get fancy and use a float switch and a motor to do that for you 

A horizontal pivot wouldn't work too well if the bridge sagged or it's foundation moved even slightly. The ones you see for roads have massive foundations and are counter-weighted to help with that and this requires more engineering than it seems on the surface.  Something which might work better along these lines would be to lean the pivot point toward the hilltop so that as the bridge pivots it also rises, and once clear gravity would return it into place. I know a man who did that with his mailbox after snowplows destroyed it several times- now it swings out of the way and resets all by itself!

Phil


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## Sparky617

One of my Eagle Scout candidates did a project in our local park with hiking and mountain bike trails.  The bridge was right on top of the ground on both sides of a small intermittent stream. When we had a major rain event the bridge became a choke point and caused more erosion.  We raised the bridge for his Eagle project.  Simple solution and you won't need to mess with walls, pivots, cables and all the rest.  I agree with MC when you start messing with waterways it isn't a simple project.  The permitting process can be quite difficult.


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## Sparky617

Here are a few photos from the project.  I don't have a finished picture of the project with the ramps installed.  The bridge actually had a small excavator go across it several years ago and it took the weight.  Since it was completed about 7 years ago it has survived many large rain events and the erosion on the banks seems to have stabilized.

We moved the bridge out of the way in one piece after cutting it free from the footings and popped it on top of the structure we built to raise the bridge up.


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## nealtw

I think the idea is interesting but I agree, disturbing the bank could effect the flow and any fish that might be there and be more trouble than it is worth.
A raised bridge giving lots of clearance makes more sense. The far side is already showing stairs up the bank so going higher and having some stairs on the near side will not make it harder to cross.


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## chris_evans

Thanks for all the replies! The banks are stone.

I am totally ok with chaining the wood to a tree and fetching it after a massive storm.

I also looked into cable bridges (lots of good stuff online), but the water lvl comes to high, i mean I really would need the bridge high. The water lvl can get all the way to the tree you see on the far side of the bank in my image.


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## oldognewtrick

How about a draw bridge, work in days of ore'...just a thought...


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## chris_evans

I can't do that because to go above the 100 year flood mark i would need a like 25-30 foot bridge.  Also, in inclement weather I wouldn't be there to raise it and if I get a dog and let them out to go to the field across the river, I don't want to walk downstairs to lower a bridge. This is why I was considering a suspension at the flood line, and if it broke in a hurricane, it wouldn't clog any culvert.

But this smaller bridge that can wash out I think is a good idea. It doesn't need to slide nicely, it just needs to get out of the way when the stream is like six feet higher.


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## slownsteady

I think you're underestimating the base for a bridge like that. That has more of a chance of washing out than the bridge itself, since it will be in the floodwater sooner and longer. You also didn't say what the bridge was made out of, as the weight will dictate a lot of the problem.
Love the view from your window BTW. I would watch that more than TV.


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## Sparky617

I wouldn't worry about the 100-year flood level in designing the bridge.  I'd go for what you typically see.  If you can build it up above the normal heavy rain flood and design it that the water can wash over the bridge, so not a lot of pickets to impede the flow and get clogged with debris, you should be OK.  A bridge is going to weigh a lot, the structure to hold your pivoting bridge would need to be massive. 

One of our other Eagle candidates built light weigh bridges for a park that could get swept way by flood waters.  They were chained to nearby trees to keep them from going too far.  That said, his were about 8' long and were more of a boardwalk over swampy land that occasionally flooded.


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## Mastercarpenty

I was thinking in terms of what Sparky is talking about: a lightweight bridge easily reset. Or a drawbridge which can be easily counter-weighted. There's really no flood line here, only a lowest elevation at which you can tolerate the number of times when the bridge will have to be attended to. 

My rather insane mind has produced a thought which might work here- an over-counterweighted drawbridge which automatically raises itself when water reaches a critical level using something like a mechanical 'float switch'. Then all you'd have to do post-flooding is pull it back down with maybe 50# of force and reset the 'switch' to hold it there until the next flood, I'm stuck on the 'switch' though- it would need to be utterly reliable and able to withstand nature's normal effects like rust, winds, and small tree debris falling on it. 

Maybe someone here can come up with something along those lines in the next few days. _The more minds you have working on something, the sooner the solution will be found!_

Phil


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## bud16415

Your animation is nice as is your photo out the window, but to be of any real help we would need an exterior photo or two showing point A and point B being where you need to get from and where you need to get to by foot. It looks like you walk down hill and then come back up hill to enter your house. A longer span might give you the height you need and make your travels easier, We just don&#8217;t know enough details. We would also need to know a budget you have for the project and if it is a DIY what skills and equipment you have to get the project finished. The jackknife bridge you show is possible I think but as mentioned by others might be quite involved getting it anchored in place and made to operate. 

Also your view is quite amazing I&#8217;m guessing you will want something that that is fitting with the landscape.


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## slownsteady

Mastercarpenty said:


> I was thinking in terms of what Sparky is talking about: a lightweight bridge easily reset. Or a drawbridge which can be easily counter-weighted. There's really no flood line here, only a lowest elevation at which you can tolerate the number of times when the bridge will have to be attended to.
> 
> My rather insane mind has produced a thought which might work here- an over-counterweighted drawbridge which automatically raises itself when water reaches a critical level using something like a mechanical 'float switch'. Then all you'd have to do post-flooding is pull it back down with maybe 50# of force and reset the 'switch' to hold it there until the next flood, I'm stuck on the 'switch' though- it would need to be utterly reliable and able to withstand nature's normal effects like rust, winds, and small tree debris falling on it.
> 
> Maybe someone here can come up with something along those lines in the next few days. _The more minds you have working on something, the sooner the solution will be found!_
> 
> Phil


It doesn't have to be electrical, perhaps just mechanical. A float or some kind of flow meter can trip a latch and raise the bridge.

hey Phil, are you referring to us a thousand monkeys with a thousand typewriters....????


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## Mastercarpenty

Minds? I lost mine years ago, and now I can babble and drool with the best of them.

I've still got my old manual typewriter. In today's terminology it's a "carbon-neutral word processor" and I still bang on keyboards from learning on one.

An idea for a latch for the drawbridge (a better word than 'switch') hasn't come to mind yet. Anything simple might release under slackness after someone walks across or present so much friction that it doesn't release when needed. Perhaps something like a hasp and staple where something catches the water current and pulls a pin out of it? Gotta be a simple effective solution for this!

Phil


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