Need to build a simple cheap concrete low water crossing over a small creek. It is dry 40-50% of the time, has a periodic 6"-10" flow, and a couple times a year after a big rain in the right spot it will blow through at 6 feet deep. Landowner has previously tried a half-hearted culvert crossing but a big rain blew it out. Located east of Navasota in a little arm of the Piney Woods so soil is almost pure sand till you get several feet down.

We can get a concrete truck to the spot and we know enough to muddle through placing it. Question is do you need to dig it out a little to anchor/form it or will the weight keep it in place? I assume we need some steel in it, will mesh work? How thick, 4"? I have heard to put some rock down first then mesh & concrete - is that needed, small gravel or bigger Bull rock sized? Any other info please.

I'd set it in the ground a ways especially on the upstream side, and go ahead and place a couple of culverts in it for normal stream flow, to reduce erosion, and probably make the rest of the pours easier. Some steel will be needed, or weight will break it up, and the ends must be fairly well built and anchored and Slope up out of the high water flow level or they will erode in a flood.

In for the environmental and floodplain advice.

thanks for posting, was going to do the same thing here in a few weeks. what we did was just place bags of cement in the washed out hole and that worked for about 9 months. it has since been washed out in some spots and then this past weekend one of the bigger trucks got stuck and broke it apart. we'll be doing some redesign here soon before the wet season.

what diameter culverts do you suggest?

I'm a professional (civil) engineer, and do this exact thing for a living. I'd like to do an informative, "how to" tutorial on this, complete with a free design for either of you. However, I'm going to need some site-specific info. Can you email me with the location of the crossing? Email's in my profile.

1. Pay someone to do an jurisdiction determination for WOTUs
2. Apply for a Nationwide 4O4 permit
3. Pay stupid money to a mitigation bank
4. Wait 90 days

email sent

Hahahahaha 90 days, yeah that's a hope and dream.

More information would need to be gathered all of which would come from the wetland delineation and the planning for the crossing. I would not be worried about the floodplain impacts though a floodplain permit may be needed depending on the county. But would be granted due to the general negligible impact to elevation of a low water crossing.

FIDO 96 said:

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-1. Make sure the property and perennial stream isn't in a Spanish or Mexican Grant and therefore the property of the Permanent School Fund.
0. Make sure the wet part is well short of 30 feet wide so it isn't statutorily navigable and therefore the property of the Permanent School Fund.
1. Pay someone to do an jurisdiction determination for WOTUs
2. Apply for a Nationwide 4O4 permit
3. Pay stupid money to a mitigation bank
4. Wait 90 days

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tamc93 said:

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In for the environmental and floodplain advice.

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Only took 10 posts plus a free design....new record?

Might look in to some sort of concrete seep collar to prevent a seam from forming underneath it. Maybe a foot across, two-three feet down in to the soil, and bank to bank.

There are more than a few of us who do this type of work on the OB.

cledus6150 said:

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There are more than a few of us who do this type of work on the OB.

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Understood and I may know a thing or six about it as well....

So it sounds like a footer/anchor trench on the upstream side in bottom and up the bank. Dig out, at least on upstream side.

If I use steel mesh and pour it thicker - 8" will that improve longevity?

What about the concrete mix? Most I have seen/used look like they have more aggregate? Regular 3000psi mix?

I could tell you what I've installed in the past in similar situations, which would end up being a conglomeration of about 10-12 different designs.

No matter what, go deeper and thicker than you think you'll really need. You are already doing the work, might as well do it one time instead of multiple.

rsmithtesiusa said:

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So it sounds like a footer/anchor trench on the upstream side in bottom and up the bank. Dig out, at least on upstream side.

If I use steel mesh and pour it thicker - 8" will that improve longevity?

What about the concrete mix? Most I have seen/used look like they have more aggregate? Regular 3000psi mix?

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4000psi mix, stay away from the 3000 mix designs. Not much more cost per yard, far better quality of concrete. I'd recommend a water reducing admixture, especially since you are remote.

If your impact is less than .10 acre (most likely) and it is not a wetland, you are authorized under Nationwide permit #14, with no Pre Construction Notification required.

Go forth and conquer.

Now we're talking - keep it coming please

Buy a 18-wheeler flat bed trailer that is no longer road worthy. Pull it to the creek. Once the trailer is in the spot you want to cross, cut the axles off from underneath the trailer. Use a backhoe to dig out both sides of the creek bed where you want the crossing. Drag the remaining trailer (without axles) across the creek. The front and rear of trailer will be laying on the "notches" the backhoe made. Use the excavated soil to backfill both ends of the trailer. If you measure correctly, you should have the 10-12" of clearance you want to keep the trailer above the water line.

aggieband 83 said:

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Buy a 18-wheeler flat bed trailer that is no longer road worthy. Pull it to the creek. Once the trailer is in the spot you want to cross, cut the axles off from underneath the trailer. Use a backhoe to dig out both sides of the creek bed where you want the crossing. Drag the remaining trailer (without axles) across the creek. The front and rear of trailer will be laying on the "notches" the backhoe made. Use the excavated soil to backfill both ends of the trailer. If you measure correctly, you should have the 10-12" of clearance you want to keep the trailer above the water line.

Same concept - but rail car

http://onlinepubs.trb.org/onlinepubs/trnews/trnews234flatcarbridges.pdf

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A great idea for a bridge.

Put down/bury railroad ties, say two wide, along each track with stone riffraff along the sides of 'runners'. Not so expensive and if done correct could/should last years

samsal75 said:

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Put down/bury railroad ties, say two wide, along each track with stone riffraff along the sides of 'runners'. Not so expensive and if done correct could/should last years

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Best, and most economical idea yet, while still very functional.

I was gonna suggest digging out the crossing bed to a depth of 8" or so, and fill it with rap rock rather than a more expensive trailer bed or rail car. But I think the railroad ties are all you'll need, and for less cost.

aggieband 83 said:

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Buy a 18-wheeler flat bed trailer that is no longer road worthy. Pull it to the creek. Once the trailer is in the spot you want to cross, cut the axles off from underneath the trailer. Use a backhoe to dig out both sides of the creek bed where you want the crossing. Drag the remaining trailer (without axles) across the creek. The front and rear of trailer will be laying on the "notches" the backhoe made. Use the excavated soil to backfill both ends of the trailer. If you measure correctly, you should have the 10-12" of clearance you want to keep the trailer above the water line.

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I would love to watch that contraption when the 6' wall of water hits.

My uncle had this idea and I said the same thing. The lightbulb moment was pretty funny

It's just a 6" thick bridge basically. If anchored into the banks enough water will go over and under and not give it much thought.

If it becomes a log jam and is then pounded by crazy high CFS, then ya your scenario would come into play.

I am in East Texas on a pretty tame creek. The prior owners did this and we normally have 8 feet of clearance.

I've owned the land for about 4 years and the water has come over the bridge twice. The 1st time it washed out the edge of one side and the bridge was half suspended. I had a friend (bulkhead/lake house company) come with a big backhoe and repaired. Also sank some pipe legs about 10 feet deep and welded the "bridge" to it. The second time was fine. I feel like it will always be hit/miss and need large repairs at times.

But I'm with the previous posters, there are better ways than the 18 wheeler bridge.

Not sure why the numbered list including actually waiting for a permanent was thrown out. Based on a number of crossings we have on a regular basis, I'm assuming the impact would be less than 0.10 acres but good to confirm not a wetland.

Also, In reference to a few posts above, depending on the project scope 45 days is pretty reasonable right now..

Here is a detail from my current project:

https://imgur.com/a/isZO6yj

Moses25 said:

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Here is a detail from my current project:

https://imgur.com/a/isZO6yj

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Looks very professional! Don't forget to put some sort of grid over the 4" pipe culverts to prevent small logs/sticks from getting wedged inside.

Buy a surplus Bailey bridge.

Get 3 buddies and a few cases of beer.

Step 1 figure out how much water is in the creek.

(Note: HighVelocity's example may be too large for a cheap-but-good low water crossing, because it's a pretty large creek. I'll try anyway).
I like to use this website: http://tfsfrd.tamu.edu/planmylandoperation/
You'll need to zoom into the location where you want to build the low water crossing, and then use these two buttons to measure the area that drains to the stream. It helps to toggle between "hybrid", "topo", and "Hydro" on the background map selector. You need to measure both the total drainage area (ie: geographic area which drains to your particular spot in the creek), and the stream centerline length to the top of the drainage area.



So from that we know the drainage area is about 560 acres, and the stream is about 6,200 feet long.
Next, decide how often you want it to overtop. Everywhere in Texas east of Midland will have 3+ rains each year that are >1". If you size the structure to contain a 1" rain, but to overtop on bigger rains, you'll be able to use your crossing almost all the time. You could choose a smaller value, which will just mean that your low-water crossing is passable less often. I'm going to use 1" of rain for this example.

So, your low water crossing should be capable of draining 1" of runoff, over the entire watershed. For this example, that's ~560 acres * 1" = 46.7 acre-feet = about 2 million cubic feet of water. If you assume that the water moves down the drainage area at 1 foot per second, that volume of water will drain out in approximately 6,200 feet / 1ft/s = 104 minutes. (Engineers: Yes, there are better ways to calculate this, but they're all much more complex. This is intended to be quick, simply, and to not require an engineering degree.)

So the flowrate (Q) for HighVelocity's crossing will be 2,000,000 ft^3 / 104 mins = 300 cubic feet per second.

Step 2 Size the culvert
Water velocity in a culvert can vary from about 2-ft/ second (for very slow bayous) to 20 ft/s (for solid-rock, Hill-County crossings with high head pressures). Flowrates over 8 ft/s generally require special erosion control to keep from washing out the downstream culvert face. Let's pick a mid-to-low value. So assume that water goes through your culvert at V=6 ft/s.

Q = V * A.

From previous post, Q= 300 CFS. V = 6. So A needs to be 50 about square feet. You need a culvert with a cross sectional area of 50 square feet. Each barrel of a 48" culvert has 12.5 square feet of area, so this creek's going to need 4x 48" diameter culverts. This will result in a crossing that's overtopped (on average) a few times per year.

Corrugated metal culverts (round) are the cheapest kind. Next cheapest is HDPE (plastic), and then round concrete culverts, with concrete box culverts being the most expensive. In most Texas clays, galvanized metal will last 15-20 years before rusting out. HDPE will never rust out, but it may float out.
If you want your crossing to last 20+ years and still be inexpensive, use HDPE culverts. Bonus: They're so lightweight that you don't need equipment to move them. You'll just need to anchor them against floatation, which is Step 3.

About the culvert slope: You want these things pretty flat, to keep the flow velocities low. Don't place them over 1% flowline slope, and preferably more like 0.5% (which is 1/16th of an inch per foot). So if it's 30 feet long, then you'd need 0.15 to 0.30 feet of rise. If they're steep, you'll get high velocities for low-flow conditions, which quickly results in LOTS of erosion. If your streambed slope is steep, leave the downstream end at grade and dig the upstream end deeper so that the culvert slope is pretty flat. If your streambed slope is already pretty flat, just lay the culverts in the stream bed and fill over them.

Step 3 Headwalls

You need to firmly anchor your culverts so that your crossing can be overtopped without the whole thing washing out. You'll want a cast-in-place concrete headwall for each exposed end of the culvert. You are really just adding lots of weight around the culvert openings.

Here's what I like to do:

Cut the pipe to match your finished slope and then pour 12" of concrete around each culvert tip.

The most critical part of the headwall - the toe wall - isn't shown in that photo (because it's below ground). Where your culvert ends, dig a trench that is 6 to 12 inches wide and 3 feet deep. Fill this trench with concrete. This allows some erosion to occur without undercutting the toe wall. If your toewall ever gets undercut, your structure is in serious danger of failure. What you want is some warning before it all gives way, so allowing 2+ feet of erosion to occur before you have to fix it is ideal.



You'll want some reinforcement to hold this together once it cracks too. Here's TxDOT's rebar detail for a structure like this (but ignore the cross-runner pipes because you're not building a highway here):

ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/cserve/standard/bridge/setpcdse-20.pdf