Another bridge over troubled water

Well, not troubled.  But certainly water.

Dad's property has a couple beavers on it, they've dammed up a good portion of it.  He keeps it flowing and I help when I get up there.

On the main dam is a cut through for the water as it's just too big for a pipe.  We've idly talked about building a bridge over it in order to access the other half of the property with trucks and whatever vehicles we might want to head over

Anyone have any thoughts as to how best to accomplish this?  I keep wondering how expensive I-beams are, maybe with some concrete footers at either end?

From level to level is probably a 10 ft span, but shore to shore is maybe 4-5 feet.  Gonna want it tall though as the wood you see here gets washed downstream once a year at a minimum in a heavy rain.

As a reference for how high the water can get, these are taken the same day, I just opened a hole in the dam

I'll see if I have a wider shot of the crossing

So, work is gonna be clearing stuff out.  Might need a trailer to haul it off, but that rectangular stuff?  1/2"x4"x6" I think?  Its probably gonna get tossed.

If I'm doing my math right, a 6000lb (ish) truck as a point load will give maybe a 3" deflection on one beam only on a 20' beam?  So two would be sufficient for a bridge?  Concrete footers?

The greyed out section would be poured underground, rest in a form on top?

The ford

The best easiest bridge I've seen was on a project I worked on recently. Basically they reclaimed a retired flat bed truck trailer frame and dropped it over the stream, then added some timber cross decking. 

it was strong enough for us to drive heavy equipment across.

40' span for the scrap value of a decommissioned tractor trailer frame. Voila!

In reply to SV reX :

This is the answer.   My buddy used one across a small but deep ravine in the back of his land so he could bring equipment and supplies to a pole barn he was building back there.  

Cheap, and turned out great.  He later turned into a deck after he was done and bulldozed a road to the pole barn.

No way would we be able to get a 40' trailer to that spot, especially a decommisioned one that would be on another trailer and would require equipment to remove.  Dad's driveway is purposefully windy, there's another creek already bridged you have to cross and a 20' work trailer won't cross it

Gonna have to be something we assemble there.

In reply to Mr_Asa :

That's what blowtorches are for.  You said you only needed to span 10'. 

Get a gator to introduce to the beavers? 

Can't help with load calcs, materials, etc., but my wife's a landscape architect, does a lot of work in the woods. A cheap/easy way to do footings for small bridges is ecology blocks:

...though maybe more than what you need?? Also, could use quarry spalls to stabilize soil below. Obviously assuming that the blocks would be placed where the soils won't get saturated.

Also, depending on regulations and/or how your dad feels about beavers in general, a Beaver Deceiver may be useful...

A little backgound: When I had the dam built (a low ground-pressure excavator with a 1 cu.yd. bucket, on the one occasion it all dried up), we installed an 18" culvert pipe just up from the overflow spillway.  Both work as they should, but in heavy rain, the two of them just can't handle the volume.  Every property upstream of me sheds into my creek.

I have had the dam wash out twice, at the near end; each time I got 15 yards of fill brought in to fill the holes. and I built the dam a little higher.  The third time it happened it was at the far end, so I just left it, shoveled the edges down to make it into a sort of ford that could be driven across, filled the bottom with chunks of concrete.  That has worked well, except the beavers keep stuffing the mouth closed.  Nightly.

I've uploaded some other video and images to Google Drive, but I'll let son Asa insert them.  That 4X6 is 16 ft long, and it still doesn't sit on the highest spots on either side; it washes downstream regularly, several times a year.  Pain in the a** to drag it back up.  The dam is my only access to the other half of the property, unless I want to wade, carrying whatever tools I might need.  The foot boards are a compromise.

My only concern with concrete footers would be that truly high water would excavate around them. 

As you guys can see here, a 10 foot span may be a bit of an understatement for Florida's multiple yearly Big Rains

I wonder what these will go for: auction

But it might be overkill and not easy/possible to get to the final location. (Although maybe attach an old axle and chain to tow it out there)

An old roll back deck could be an starting point  

Asas_Dad said:

 

...and I built the dam a little higher.  The third time it happened it was at the far end, so I just left it, shoveled the edges down to make it into a sort of ford that could be driven across, filled the bottom with chunks of concrete.  That has worked well, except the beavers keep stuffing the mouth closed.  Nightly.

If you can drive across the dam now, and have sufficiently shored it up to tolerate the rain, then it seems a bridge would be unnecessary, if you could thwart the beavers. Check out this video:

But who's to say you won't get a larger storm event than you've already had, in which case, how hard would it be to replace the culvert with a larger one, or add another one adjacent to it? I'm not an engineer, but my bet is you could find 100-year-event flow data pretty easily (e.g., USGS, or your state environmental agency), and ensure that your culvert capacity is sufficient. In the end, it seems simpler to keep the dam wall intact than building a bridge, and even if you don't add storm-event capacity, a majority of the problem would be solved with a Beaver Deceiver. FWIW.

In reply to procainestart :

100 year flood data feels like it might be worthless as the beavers are a problem within the past 25ish years, but I may be missing something about how it's calculated 

In reply to Mr_Asa :

I had to go to the internet to find out when the 100-year maps were drawn; it appears to have originated in 1968, when Congress established the National Flood Insurance Program.  I haven't found who originally drew the maps, I'm assuming private surveyors because I can't find otherwise.  

  The original maps were notoriously inaccurate, as Stampie can testify; his property has been resurveyed, now reflects reality.   The guy that granted me permission to build a dam across my swamp paid thousands to have his own property surveyed  to contest inaccurate flood zones - and he worked for NWFla Water Management!

In any case, the maps are not germane to this; I changed the flow by building the dam, and the beavers have changed it before and after my dam.  They have built at least 8 dams, have flooded approximately 9 acres that were previously well-drained wooded bottom.

procainestart said:

 

But who's to say you won't get a larger storm event than you've already had, in which case, how hard would it be to replace the culvert with a larger one, or add another one adjacent to it? I'm not an engineer, but my bet is you could find 100-year-event flow data pretty easily (e.g., USGS, or your state environmental agency), and ensure that your culvert capacity is sufficient. In the end, it seems simpler to keep the dam wall intact than building a bridge, and even if you don't add storm-event capacity, a majority of the problem would be solved with a Beaver Deceiver. FWIW.

One thing to note here, there isn't actually a culvert that we're trying to bridge.  Its basically a channel through the dam, water gets high enough on the dam and flows through like a small creek.

In reply to Mr_Asa :

Yes.  The original question by Asa was on the order of "Any ideas on how we can bridge this cut in the dam with the steel my firm is going to be scrapping?" 

Although that's an engineering question, and my son IS an engineer...

Asas_Dad said:

In reply to Mr_Asa :

Yes.  The original question by Asa was on the order of "Any ideas on how we can bridge this cut in the dam with the steel my firm is going to be scrapping?" 

Although that's an engineering question, and my son IS an engineer...

Tight Dad burn, +1

SV reX said:

In reply to Mr_Asa :

That's what blowtorches are for.  You said you only needed to span 10'. 

My brother in law built a footbridge using the frame from an old pickup, one of them will easily span 10'.

In reply to Asas_Dad :

This is a question for the civil nerds.  I'm mechanical.

Also, I like seeing what these guys come up with.  I like the trailer idea, I just don't think its feasible for the dam road

For a little perspective, my town is currently constructing a footbridge (10' wide wooden boardwalk) across a creek near my home.  The span is about 40'.  Budget is $1.3 Million.

In reply to Mr_Asa :

What about using the frame from a travel trailer reinforced with scrap steel and decked in wood?

Easier than to move that a freight trailer, and if you don't mind evicting snakes and spiders, probably a low cost base. 

In reply to No Time :

Possible, for sure.  Brother in law has an old travel trailer on his land he might want to get rid of.  I'll ask next time I see him

Manufactured homes are built on narrow I beams typically 10"x3". Find an old 50'x11' trailer house, demo the structure and pull it on it's wheels to your location.

Mr_Asa said:

One thing to note here, there isn't actually a culvert that we're trying to bridge.  Its basically a channel through the dam, water gets high enough on the dam and flows through like a small creek.

Is this what you're trying to do?