Need to solve flooding for old bridge

[Stonewilled]

I have a bridge that I've repositioned over a creek in a flood plane. Pretty sandy soil on both sides. A few trees upstream and downstream on both sides. More on the side I'm standing on and fewer/further on the side she's on. That is a 3-4 inch diameter water oak growing at the corner next to the side she is on. (South bank)... Edit: water will rise up to 2-3 feet over the top of this bridge.

 

[RjCorazza]

I don't see how you can solve that with water 2-3' over that bridge. Maybe build a large arched bridge?

 

[Stonewilled]

I was thinking ballasts and rings so it can slide up rebar hammered down into soil with a sledge as far as I can?

 

[Stonewilled]

What do you think would happen if I anchored it with rebar to a Mass of concrete and kept it held down? Would flood waters just destroy it?

 

[Stonewilled]

Or chain it to large trees upstream on both ends?

 

[jyoutz]

What do you think would happen if I anchored it with rebar to a Mass of concrete and kept it held down? Would flood waters just destroy it?

Probably

 

[Stonewilled]

It has been in that bottom for ten years. With privet growing through it holding it in place. But that's when it was sitting squarely on level ground. I know that just the fact that it is over the creek means it will be subjected to far greater forces. But will it be that significantly different? Can anyone link to some good reading that covers these sorts of topics?

 

[rumwrks]

I dunno.. 2-3' of water can be a hell of a lot of force. A lot depends on how fast it's moving though.. 6" of fast water does a lot more damage than 2' of slow...

Whats the soil under it down lower? That is how deep does the sand go?

I think my best shot would be to dig three holes 4-5' or more depending on the soil.. deep and 12-18" across on each end right under each of the three beams and fill those holes plumb full of concrete with concrete post anchors between the concrete piers and the beams. There will be some .. erosion effects from water eddying around all of that that I don't know how to model.

 

[ultrarunner]

When my friend bought a similar property I said nice raft you got.

He looked puzzled and said the seller had to rebuild it as part of the sale.

I said what happened to the old one and he said washed away.

Sure enough the second winter his 2 year old bridge washed away.

 

[bcp]

Using a long cable, anchor only one upstream corner very well. When the creek floods, the bridge can swing out to the side of the main current. Drag it back into position afterwards.

If you fight it, you will lose, sooner or later. Let it go with the flow, then reposition it.

Bruce

 

[Rockbadchild]

I would say the same as bcp just tie it so it doesn't completely wash downstream or remove it before the flood season. If going with a 4 post slider type you would need floaters for it to rise with the water level but with a strong current the odds for it to lift with the water in a strong current situation, and not angle sideways and dip in the water are slim, plus there's always the possibility for logs to wash away with the current and hit the bridge. Plus sand doesn't offer the best anchorage.

 

[2manyrocks]

Wood like that can be floated away and/or the current could tear it to pieces. Is there another area where it could be moved that would be high enough to get it out of the flood water?

 

[bdhsfz6]

From your picture, it looks like a fairly wide flood plain, which may mean the flow rate during flood stage is fairly slow. If that's the case, take out the bridge, get a piece of 36" diameter pipe, throw it in the creek, put a few rocks on the upstream side to limit erosion and put coarse fill on top. Won't work if the flow is to swift though. You may also get some flak from the DEP if they see it.

Depending on who or what crosses the creek, you could also remove the bridge and make a shallow water crossing.

 

[dodge man]

I’d say putting a culvert in would be best but it might get washed out to. It looks like you can’t use the bridge during high water anyways because the approaches are flooded so you could drag it out the way if it doesn’t flood often. It it’s been there 10 years you could just leave it alone too.

 

[mocassincreekranch]

Slope both sides of the creek and pour concrete in the bottom and sides, and never worry about high water again. Culverts and bridges always wash out in flood events. Here in the hill country, most county roads have low water crossing in leau of bridges. I poured concrete in the bottom of my creek over 20 yrs ago and still in place.

 

[scootr]

I like the idea of tethering it to upstream trees using cable so it can float in place and settle back down where it belongs.

 

[paulsharvey]

How important is the crossing to you, do you have the option of pulling the bridge during bad floods, and resetting after the water receeds?

If this is a critical crossing, I would do something like double 24" CMP, With concrete head walls/Mitered End Sections (or maybe just rip rap, depending on if bolders/rock can be found local). If the creek does come up over the top, the rip rap, or MES/end walls will protect it to a pretty good degree.

The bridge looks pretty light duty; another option would be to jack it up, 24" and pour a good concrete footer, and build bridge approach ramps, to get you upto the new bridge deck level. You might not completely remove the chance of it over topping, but if you move from a 10 year flood, to a 25 or 50 year flood; that might be worth it. The bridge approach could another wood ramp, or it could be compacted soil.

It really looks like you could set and concrete 4 6x6 PT and attach the bridge on those, but elevated to an extent.

 

[JasperFrank]

I would go with the culvert ideas if you get 3' over in the entire flood plane. You will lose some of the road/gravel, but that's far easier to repair than making a new free span bridge every time.

 

[redman135]

A variation on what Paulsharvey said. Raise the bridge 4 or 5 feet so you don't need to worry about the usual floods. Ramp the approaches and cover ramp sides with riprap to stop erosian. Leave the flood plain section of the track at original level to allow high water to go around the bridge and avoid scouring around the piers. A track is cheaper and faster to repair than a bridge.

 

[bigtiller]

Is its primary purpose for vehicle crossing or human crossing and keeping your shoes dry?

A ford with a concrete bottom would solve all your problems for vehicle crossing.