Low Water Crossing (kinda long)

BB_TX · Aug 28, 2007

OK, guys, tell me I am nuts. You may remember me posting a couple years ago about trying to find an old flat bed semi trailer to drop across a creek for a bridge to make it easier to get to the other side of my property. I found one that was exactly what I needed, 40 with good steel but rotted boards and nearly flat tires and only 20 miles away. When I inquired about buying, the guy said someone had abandoned it on his vacant lot, and he would decide what it was worth and get back to me. He didn't and the trailer disappeared. I think I may have inadvertently given him an idea as he mentioned he also owned some land.
After another year and half of looking, I have found no other old trailer. Building a bridge from ground up would be prohibitively expensive due to the cost of steel and every thing else I would need. Plus I am not sure I would try it without having a civil engineer calculate the steel sizes and construction methods. The creek would need a span of maybe 25+ feet at the narrowest point I can find. The bottom of the creek is maybe 10 below grade with mostly steep sides. It usually has only a little flow. And during the summer it often dries up. It dries fast, but also rises fast. During a heavy rain period, it may flood with a pretty extreme flow for a few hours so the bridge would need to be above grade somewhat. I would prefer not to have center post supports as the bottom is dirt/mud and I think I would have to sink posts way down for adequate support as well as withstand the flood flow of stuff down the creek.
Soooo. I am wondering about a low water crossing. My thinking is that I could grade a gradual slope on both sides in an area where the sides already slope somewhat. Then I could put down a culvert. Then build a retaining wall on the upstream side and downstream side using the stacked sack concrete as was the subject of a thread (by Bird?) some time ago. (Riprap would probably work also) Then fill in between the walls and cover it with rock.
My neighbor, who is also a good friend, has a track loader. So that part is covered.
What do you think? Am I off in left field somewhere? Would it wash out with the first rain?

GaryM · Aug 28, 2007

Low water crossing would work fine, as long as you realize that there will be some times you can't cross!

I'd really think about a solid concrete topping though. If the creek really runs fast I think most anything else could wash away. The stacked sacks is a good idea though. I've seen them do that alot in Florida when they fill in aroung bridge abutments.

marimus · Aug 28, 2007

We had a similar kind of problem. This creek is dry most of the year, however it has a very large catchment, and so after rain it really roars across this crossing. Afterwards, it was too wet to cross, even with the 4WD and walking across on foot you would sink to your knee easy.

Anyway, we constructed the crossing by removing the silt layer down to the firmer clay underneath. Then we put in a load or rock (approx football size). We then concreted over the top. Water runs straight through the rock, unless there is a heavy downpour, and then it washes over the whole crossing.

We have had water 3-4 feet over the top of the crossing on about 5 occasions since we installed it a couple of years ago, and its held up really well.

Bird · Aug 29, 2007

My old posts and pictures of that retaining wall are here. I think it works pretty well in a lot of places, but I'd be surprised if it worked very well for creek banks. I would expect that to be just too much water flowing too fast occasionally. But of course that's only a guess.

wushaw · Aug 29, 2007

My neighbor did a low water crossing like what you are wanting to do since whoever built his bridge did a poor enginnering job and it became a dam and washed out the dirt on both sides.

His low water crossing is 3 ea. 36" coverts tapered on both sides covered in concrete with just crushed concrete for the road part.
Water and debris will just go over it without tearing it up.

They have two crossings...the low one and a bridge that is built just like the one that washed out, it is downstream, I am waiting on it to also wash out since he will not keep the creek cleaned out of debris.

Your low water crossing idea will work since you do not live on the other side of the creek.