Determining culvert size | GON Forum

We have 4 crossings on our drive. 3 24inch and a 3 ft pipe. Do yourself a favor and put in a plastic culvert. Not much more and will outlast galvanized. Need to clean out topsoil around creek and clean out creek bottom to bed the pipe. Only use good dirt when covering. Tamping and packing as you go. I like about 2 ft or more of dirt on top of pipe. Also need to consider how much watershed is above you. Probably have that 1 and 100 year rain event after you put it in so you want one big enough. A 3 ft pipe will handle a lot of water.

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Dmpaul89

Posted 11/22/ 14:16 (#)
Subject: How big of culvert

Sw. Ill

Do i need? Is there a calculation that works on a per acre basis? I need to install a culvert that would handle the runoff drainage from about 45 acres. And another one that would handle 80 acres of runoff.

Both fields gently rolling with grass waterways that funnel down to one gully. senorthdakota

Posted 11/22/ 14:23 (# - in reply to #)
Subject: RE: How big of culvert

Not sure how to figure but as big as neighbors let u put in hydro70guy

Posted 11/22/ 14:28 (# - in reply to #)
Subject: RE: How big of culvert

Swaledale, IA

I know to figure you will need to know how much rain per hour you want to keep away plus what kind of grass waterways If any are around to slow things up. I guess without knowing layout I would look at what county uses for roadway culverts. MGfarms12

Posted 11/22/ 15:07 (# - in reply to #)
Subject: RE: How big of culvert

South Western, IL

I used an app for drain tile. Would imagine it would be similar. It calls for a 12' but I would go with 24' at the smallest no matter where I put one in.

It's always the easiest to do the first time.

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4WD

Posted 11/22/ 17:12 (# - in reply to #)
Subject: RE: How big of culvert

Between Omaha and Des Moines, 7 miles South of I80

casefever - 11/22/ 15:09 If its in your field put one in as big as you can handle, if its going in a driveway the county will tell you what you can put in and you will buy it from them also. Probably have to file for a permit with a fee too. another words put whatyou want in and don't advertise it, maybe no one will notice, YA RIGHT!!

Story: Last Summer, I asked the county, North of me, about culverts and their Minimum is 15" for any farm driveway into a field, then there are restrictions about "line of site", also  = I think it was 450 ft each way, on a gravel road. You must buy the culvert from them, new; and they delivery for an additional 25% above the cost of the culvert.

If you can put farm field driveway on a hilltop (when water drains both ways), then No culvert is required, BUT they make that decision, not the farmer.

Also, field entrance must be 6" lower than gravel road, when done. Again, it is about drainage.

ndsu84

Posted 11/22/ 17:18 (# - in reply to #)
Subject: RE: How big of culvert

EC North Dakota

I have a prinsco calculator here somewhere. You need to know how fast you want it(x amount of rain) gone and how many acres.

But as already said, as large as you can afford that the neighbors/govt. will allow. Dmpaul89

Posted 11/22/ 17:39 (# - in reply to #)
Subject: RE: How big of culvert

Sw. Ill

its not going to a road. it will be within the farm, its a field lane. usually drive through the two gullies but id like to add culverts and level it out for easier access. Shimmy1

Posted 11/22/ 17:41 (# - in reply to #)
Subject: RE: How big of culvert

Central ND

Central ND

Around here, we have places where hundreds of acres are flowing through an 18" pipe. How much drop you have from the highest point to the lowest will factor in, and also if there are areas where the water can pool up a little before running out that will help. Getting every last drop out as fast as possible is almost always not the right thing to do for the guys downstream. Deere

Posted 11/22/ 17:47 (# - in reply to #)
Subject: RE: How big of culvert

4WD

Posted 11/22/ 17:49 (# - in reply to #)
Subject: RE: How big of culvert

Between Omaha and Des Moines, 7 miles South of I80

Just a quick Google, and this .pdf came up, from North Carolina Forestry manual, for a 2.50" rainfall per hour.

Contact us to discuss your requirements of Large Metal Culvert. Our experienced sales team can help you identify the options that best suit your needs.

 

If I read it correctly, then 45 acres of Ag land with gentle slopes, I get a number of 4.3; then take that number and scroll down and it looks to be roughly a 29" of Round pipe.

So, on 80 acres, for 2.50" rainfall per hour, on Ag land with gentle slopes, then the number was 6.6, and scroll down to the chart and it figures roughly a 34" Round pipe.

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Shimmy1

Posted 11/22/ 17:50 (# - in reply to #)
Subject: RE: How big of culvert

Central ND

Central ND

I was guessing by your description that you were going to be installing crossings in the grass waterways. How much drop do you think you have from the highest section of the field to where you want the crossing? If the land funnels the water to the waterway like a spillway, you might need a pretty good pipe to be safe in a multiple inch rain event. Without actually seeing the land, nobody on here is going to be doing anything other than shooting in the dark. You might need to talk to a local contractor or two that specialize in drainage to get the right answers. HoRFarms

Posted 11/22/ 17:58 (# - in reply to #)
Subject: RE: How big of culvert

SE VA/NE NC

Id be doing 24' and 30'. Or just 30' both to keep it simple. The problem with 12'-18', which is what i ise on tap ditches 5-20ac, is not water flow, but that they get stopped up with trash so easily. I dont think ive ever seen my 30' stopped up, and for 40+ac, I wouldnt be taking the chance. Shimmy1

Posted 11/22/ 18:04 (# - in reply to #)
Subject: RE: How big of culvert

Central ND

Central ND

This chart might work for the small acreages, but the lay of the land is going to be the deciding factor. We have several drainage networks in my county that are from to acres. Based on this chart, for level country, we should have at least a 10' pipe, and maybe bigger. These drains have 3-24", or 3-36" pipes and work just fine. If they followed this chart to a tee, our county would have washed Jamestown and Valley City off the face of the Earth years ago. hd6gtom

Posted 11/22/ 18:26 (# - in reply to #)
Subject: RE: How big of culvert

I had our county engineer stop buy and take a look at my situation. He recommended a 24" pipe. We have to buy our culverts from the county. I wanted to argue with him, but did not. It should have been a 30 or 36" pipe. If you put a 24' pipe on a 16' trailer, be careful, the back end gets to whipping side to side. This 24" pipe cannot handle the water and constantly over flows into the hay field. Go as big as you can. Varment

Posted 11/22/ 18:39 (# - in reply to #)
Subject: RE: How big of culvert

Ontario's West Coast , Huron County

You may want to consider a crossing that will allow water to flow over when big rain events happen . Low level crossing maybe ? sri

Posted 11/22/ 19:27 (# - in reply to #)
Subject: RE: How big of culvert

nw pa

Dmpaul89 - 11/22/ 17:39

its not going to a road. it will be within the farm, its a field lane. usually drive through the two gullies but id like to add culverts and level it out for easier access.

I think as others have stated, low water type crossing. something easy to cross but no restrictions. Have two made from digging out the driveway part and filling the crossing with rock. work good. dave morgan

Posted 11/22/ 20:43 (# - in reply to #)
Subject: RE: How big of culvert

Somerville, Indiana

guys at the ASC office design my crossings, lot of good advice...One of which is to install the bottom of the culvert level with the stream 200 feet downstream to keep water from trying to go under the culvert...Many are put in too high, many fail..

Edit to add: The largest here is 60 inch by 40 feet, a good 80 acres drain through it...All culverts are at least 40 ft long, most are 36 inch or larger...A 24 catches too much trash if left unguarded..

Edited by dave morgan 11/22/ 20:46

Rock Road

Posted 11/22/ 22:04 (# - in reply to #)
Subject: RE: How big of culvert

w/c Illinois

How deep is the ditch the culvert will sit in? Going big is good, but you need to have the correct amount of fill on top to properly carry the load and avoid crushing the pipe. This is especially true if you use a plastic culvert. If your ditch is shallow you can use two or three smaller culverts to get the proper cover, but they will plug easier. KDD

Posted 11/23/ 07:39 (# - in reply to #)
Subject: RE: How big of culvert

Leesburg, Ohio

Leesburg, Ohio

What would neighbors have to do with sizing a culvert? J,ReinkeFarms

Posted 11/23/ 10:07 (# - in reply to #)
Subject: RE: How big of culvert

We use the 'Rational Method' for runoff determination. There are some calculators online to help with this. Once you know your runoff volume you can design the size of the culvert or multiple culverts depending on your cover availability. Being it will be a private farm lane you have some leeway on what you want to do, just don't size it too small because you risk washouts.

Here is one that should help with runoff.
https://www.lmnoeng.com/Hydrology/rational.php
DoubleJFarmsWA

Posted 11/23/ 10:21 (# - in reply to #)
Subject: RE: How big of culvert

Eastern Washington

Low Level Crossing - On a field crossing, I have seen a small culvert (12in I think it was) in the ditch to handle the regular water, then it is flat across the top of the culvert and tapers up into the field on both sides. The ditch is about 4 feet deep (and yes at times its full). So the water runs over the culvert if necessary. The area is wide enough that the flow doesn't cut out the culvert for the water to get away. On the far side of the culvert, the taper angles the water back into the 4 foot ditch. This crossing has been in for 4-5 years I believe is what I was told. Before this, they would drag a wood bridge over the ditch when needed, or bury a temporary culvert and remove. But this last design has been working good. sed

Posted 11/23/ 20:12 (# - in reply to #)
Subject: RE: How big of culvert

southwest illinois

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Using Talbot's formula:

45 acres would need 7 sq. ft opening
80 acres would need 11 sq. ft opening

Howards Formula confirms this

Both assuming gently rolling ground