Large culvert for creek crossing???

   / Large culvert for creek crossing??? #21  
I think it would be a good idea to get some information from the USDA soil and conservation guys on how many acres of land drain into that creek above your culvert. They can tell you sizing if you ask them. Or just ask them the amount of acres and put their answer here in this thread. If they say 380 acres, that a heck of a lot more than 40 or 60.

It's not that simple, it depends greatly on the steepness of the terrain, the ground cover, etc. 500 acres in flat land is different than a 500 acre watershed in steep terrain. Our bridge floods once or twice a year. Although it may be under a foot or two of water, it only lasts for 15-30 minutes.

If the soil and water people can't help, maybe your county engineer can. Our county engineer did the calculation for me, told me that I needed twice the capacity for the bridge. I elected instead to put in concrete covered rip-rap to protect the bridge and let the water go over it, a lot less costly approach.
 
   / Large culvert for creek crossing??? #22  
I have done several of these crossings, One thing to remember it you have to remove all the sand under the culver to keep it from washing under the pipe. Compaction is the most important thing and a over flow/flow around is also will save you during a flood.

I had the county help me figure the drainage several times. For one road we put in 5 24 inch pipes to handle the flow with a very large flow around as the ground was very flat and we couldn't lower the drainage ditch with out cleaning miles off waterway. My favorite pipe is concrete.

Sounds like you have alot of water if your needing 8foot pipe, get a bunch of photo's.
 
   / Large culvert for creek crossing??? #23  
I contracted for a culvert placement to cross a small stream and gain access to property for timber management that I previously had to access across a neighbor's place. The result was a 66" diameter x 28' long culvert that was approved as "fish friendly" for fish passage. As this was timber property, the Oregon Forest Practices Act applied so the culvert had to be approved by the Oregon Department of Forestry (ODF). The ODF made the determination of size based upon the upstream watershed area, the kind and amount of excavation and fill needed, etc.) Total cost of the project was $6,300 (including aligning approaches, etc.). Cost of the culvert was about $1,300. I would really recommend seeking professional help regarding the size of the culvert and scope of the project based on the watershed, estimated 100 year flood potential, etc. Depending upon what is downstream (in my case, a county road with culverts, some yard and landscaped areas, etc.) the liability for a failed project can be significant.
 

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   / Large culvert for creek crossing???
  • Thread Starter
#24  
The property is located is south central indiana mostly flat ground so flash floods are rare and when the creek is swollen it is only for an hour or so. The creek itself terminates in a watershed/lake about 35 acres in size. Nothing downstream to be of concern. Dnr will not bother with helping out since it is not close to a roadway.
 
   / Large culvert for creek crossing??? #25  
I have found a 6' round culvert of the same material the county has used. The question is would a single large culvert be better than 2 smaller ones say maybe 2 5'footer side by side? Also would pour concrete around the pipe and pack fill in tight after the concrete. Any thoughts from those who may have done something similar?

Our creek crossing is made of three 5' diameter steel culverts 38 feet long with a foot left between each for compacted earth to support the walls. Rip-rap around the ends. Use the natural slope. If doing it again I'd use six foot diameter next time just to make it easier to walk through and clean.
rScotty
 
   / Large culvert for creek crossing??? #26  
If you can think of this channel as a spillway from a pond, you could gauge what needs to be done, or at least consider some options. I know, there's not actually a pond this is flowing from, but the (mostly) dry creek acts as a spillway would if a pond were being overflowed.

If you go to any online topo map or similar website, you should be able to get a good guess of the area that drains into this creek. Plug that area into this formula (you can use an online conversion tool to change any area measurement into acres):


Q = C I A

where: Q = peak discharge, corresponding to a given
rainfall intensity, ft.3/sec;
C = runoff coefficient
I = rain intensity, in/hr;
A = catchment area (acres)


To determine a typical case scenario, the "100 year rain" or what is believed to a rainfall amount that comes about once every 100 years:

hdsc.nws.noaa.gov/hdsc/pfds/other/mn_pfds.html

Take the number you find at the website and insert it as I in the formula. (the site also give expected rainfall amounts for other storms, like maybe every 10 yrs, 25 yrs, etc)


This table will help you determine C for the formula:
Values of Runoff Coefficient (C) for Rational Formula

http://water.me.vccs.edu/courses/CIV246/table2_print.htm

Land Use C Land Use C
Business: Downtown areas Neighborhood areas 0.70 - 0.95 0.50 - 0.70 Lawns: Sandy soil, flat, 2% Sandy soil, avg., 2-7% Sandy soil, steep, 7% Heavy soil, flat, 2% Heavy soil, avg., 2-7% Heavy soil, steep, 7% 0.05 - 0.10 0.10 - 0.15 0.15 - 0.20 0.13 - 0.17 0.18 - 0.22 0.25 - 0.35
Residential: Single-family areas Multi units, detached Munti units, attached Suburban 0.30 - 0.50 0.40 - 0.60 0.60 - 0.75 0.25 - 0.40 Agricultural land: Bare packed soil *Smooth *Rough Cultivated rows *Heavy soil, no crop *Heavy soil, with crop *Sandy soil, no crop *Sandy soil, with crop Pasture *Heavy soil *Sandy soil Woodlands 0.30 - 0.60 0.20 - 0.50 0.30 - 0.60 0.20 - 0.50 0.20 - 0.40 0.10 - 0.25 0.15 - 0.45 0.05 - 0.25 0.05 - 0.25
Industrial: Light areas Heavy areas 0.50 - 0.80 0.60 - 0.90 Streets: Asphaltic Concrete Brick 0.70 - 0.95 0.80 - 0.95 0.70 - 0.85
Parks, cemeteries 0.10 - 0.25 Unimproved areas 0.10 - 0.30
Playgrounds 0.20 - 0.35 Drives and walks 0.75 - 0.85
Railroad yard areas 0.20 - 0.40 Roofs 0.75 - 0.95
*Note: The designer must use judgement to select the appropriate "C" value within the range. Generally, larger areas with permeable soils, flat slopes and dense vegetation should have the lowest "C" values. Smaller areas with dense soils, moderate to steep slopes, and sparse vegetation should assigned the highest "C" values.

Once you have the numbers, multiply C x I X A this gives you expected maximum flow. I believe these sites also have more info on picking pipe sizes, etc.

The charts are a lot easier to read than what I can copy/paste, too.
 

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