# Suggestions for a fallen tree bridge



## Stevob (Feb 27, 2009)

We have a fallen tree which we would love to convert to a bridge. It would join the trail across a shallow gully nicely, and avoid some potential erosion issues where the track currently runs, further up the gully.




























Some things about it...


The tree is quite capable of holding the weight of a couple of riders.
It has no inclination.
It is about 12-14" wide at most.
The entry point from the track is nearly the same level as the tree.
The exit would involve a small climb
It is about 5 metres long.
It is about 1 metre off the ground in the middle.
The local trees are mostly small diameter tea tree and some small gums.

Does anyone have any suggestions for the best construction method to use to make it into a sturdy bridge? Or is something like this not advisable?


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## Ridnparadise (Dec 14, 2007)

The tree is at the right height for a bridge to suit the masses. It would be a scare to many riders though, being quite narrow. The big questions are risk and sustainability. If this is a public trail then I see 3 options.

The first is shaving the upper surface of the trunk and adding 45cm slats, plus a B line through the creek if possible. 

The second is getting an expert chainsaw ninja to horizontally split that trunk into 2 halves, anchor the removed upper half next to the mother and plank it out to a wide bridge. 

The third is a compulsory B line and just shave and texture the trunk (eg angled saw cuts leaving a remaining tread) and leave it as a 20cm challenge.

That there looks like it has been there for a while though. Do you really think it will be safe in 5 years, no matter what you do?


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## Stevob (Feb 27, 2009)

It _has _been there for some time. I was going to consider some form of support bracing for longevity. Not sure on the splitting in half idea, seems as though it would lessen the load bearing capacity of the trunk a bit. I know the planks would spread the load though, so it's maybe not as concerning.

There is already a B line (where the track currently runs), so that's no issue. I like your first idea of the 45cm slats on top of the shaved trunk. Might give that a go.

Thanks heaps for the suggestions.


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## Ridnparadise (Dec 14, 2007)

I'm no bridge expert, others do that here, but by cutting into a log you can find hollows and weaknesses that may be a risk. If you have doubts about the log, then cut into it fairly deeply.

Your choice is definitely the best, but anchor each of those slats in 2-3 sites for stability (legal stability). If you are able to cut the trunk deeply enough, it may be possible to use the offcuts as the slats. Flip em over and ride the rounded rough side. You could get 2 per length if you cut a deep enough slab. Having said that it leaves you with 3 of the 5 metres without slats so you would need more local timber to create a rough round-top bridge, but it would look really cool and "local".

Looks good. Show us how it goes.


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## Stevob (Feb 27, 2009)

I do have some reservations about what condition the inside of the trunk will be. We'll soon find out though, and it won't be used if it's too risky.

I just managed to procure some nice hardwood which I can cut up for slats. It arrived courtesy of our home renovations.


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## J. Johnson (Feb 20, 2011)

Yikes. Be very cautious here. Bridges are major source of hazard -- and liability. In the first place, most jurisdictions require hand-rails on over four (sometimes three?) feet high. Less than that, well, it's perfectly okay if people keep falling off and tromping around in that creek? Or just by-passing this challenge?

Second, that log is pretty far gone in regards of deterioration, and any cutting into it is likely to cause it to fail. (Sooner, that is.) What do you do then?

If you need a bridge you should consider if you can drag in some prepared logs. Or if you have enough rock around you might see if you can build a ford. Or, as a last resort, bring in a culvert. Whatever you do, check with the landowner/land-manager first.


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## Stevob (Feb 27, 2009)

We don't _need _a bridge. I was only seeking feedback on whether it could work out as a trail feature, with a definite B line option.

If we can make it safe enough to ride over we may use it, otherwise it will not be utilised. I shall get a mattock down there and shave a bit off to see how far gone it is.


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## Ridnparadise (Dec 14, 2007)

Go for it Stevo. :thumbsup: 

Never ridden a bike without risk. Ripped my toe off at age 7 on the road outside my house when my thong'd foot slipped into the spokes, then the fork and there ya go. They flipped it back over and stitched it down with maximum attention to painful needles!

Make that alternate line with a fun 5m bridge. It's not the Golden Gate, it's just a line to ride if you want to. If you prepare the log and it is rotten, then that's that. Cut it through and just walk away.

Pleasure when riding your trail will instill confidence and reduce injury. Not only that, but riders see what you have done and take that into the next generation of trailcare. 

Call me an anarchist, but done quickly, sensibly, with thought to safety rather than legality and maintained carefully without attracting attention to your digging:thumbsup:  then in the end it will be fine.

Summary. Make it well, think of the sustainabilty of the trail and make it fun. Look after it and all will be right in the world.

There are bunches of these bridges in my local area. They are cool. More dangerous to walk than ride though, so there has to be a B line and you have to be able to see them in time to assess your own risk as a rider. Litigation shmittigation


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## cjohnson (Jul 14, 2004)

*uh*

that tree looks half rotted. definitely shave A LOT of that top off to see what you have to work with.


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## Stevob (Feb 27, 2009)

The tree is a sharp right hand turn off the main line, so accidental riding most likely won't happen.

I'll take a cordless drill and a large bit and do some investigation. There's a good chance the core is rotted. Happens a lot around here.

Don't be too concerned everyone. It won't get used unless I know it's safe.


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## zrm (Oct 11, 2006)

I'd give very good odds that tree is toast.


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## HighFivenWhiteGuy (Apr 5, 2011)

As much as I would like to see you turn that into a log ride, I have to agree with the consensus here... not all that safe. Too bad, perfect spot for one. Any other downed trees nearby? Make friends with an owner of a grip-hoist and make your own crossing!


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## thefriar (Jan 23, 2008)

Just do it...
http://pics.bikerag.com/showphoto.php?photo=14071

take a look at the gallery for more skinny ideas, this place is better than any other place out there for skinny riding.


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## rottendan (Dec 17, 2008)

go for it.


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