Culvert installation into running streambed 1

[rogerrogers]

We would like to install a culvert in a running streambed, in order to provide better access to a back lot on a farm.

The stream is small, I don't know flow rates, etc, but I would say it is 2 inches deep, 18" wide, at the most. The flow rate doesn't appear to change dramatically, even after large rains, as the stream originates not far from where we need to cross and isn't fed by a major run-off.

The creek bed is somewhat marshy, with really solid soil starting about 5' on either side. This is the best point for crossing, otherwise we'd try to find a place with drier surrounds.

With that context, we are curious to know what we should do to stabilize the creek bed prior to installing the culvert. The culvert size we are planning to install is 36". Should we put a certain kind of gravel in? Should we install the culvert parallel to the stream and then divert the stream to flow through the culvert, giving us a drier working area? Should we surround the culvert with gravel, or just backfill with soil from the vicinity? How much soil should we cover the culvert with in order to cross the culvert with heavy farm equipment, including excavators?

Any advice is greatly appreciated, as this is a DIY project and we don't have much experience.

 

[civilperson]

What material is the 36" culvert made of? If reinforced concrete pipe is used and the wall strength is similar to Type 3, then dig down 18" below the flowline of the creek and place 6" to 12" of sand/gravel for a base. Place the pipe lengths, (width of road plus 9' for slope), and fill to the top of the pipe. A foot of well compacted fill, (original soil), above the top of culvert and then a 4" gravel road should suffice. Head walls can shorten the required length of pipe culvert and extra fill on top of the culvert can allow substituting CMP for the culvert.

 

[rogerrogers]

Thanks for your response!

The culvert is metal, so we'll add extra fill over the pipe. Also, how much lower than the stream should the metal pipe be inserted? Would it still be 18" below the flowline?

 

[rconner]

With your topography and hydrology/flow conditions, will this have to be a "siphon"?

 

[rogerrogers]

Can you explain more about what you mean by "will this be a siphon?", at least in this context. Do you mean drain the water out first?

We are currently planning to dig a new trench for the culvert and then redirect the stream through it, once installed, so that we aren't working in the mud.

 

[fattdad]

Not to rain on your parade, but you likely need a permit to do this work. Streams are protected just like wetlands and your state environmental agency and/or the Corps of Engineers may be involved. Also, you may face the need for mitigation for the impacted section of stream/wetlands, which can get expensive!

f-d

¡papá gordo ain’t no madre flaca!

 

[rconner]

I guess I originally misunderstood what you meant (I now understand better that you are just wanting to build an access in effect ROAD "crossing" to bridge over a stream, which means the stream basically WILL flow through the culvert you are talking about!)

 

[cvg]

recommend the culvert should be installed at the same level as the existing stream. If you lower it, it may just fill in with sediment anyway. However, if you are using a 36" culvert to cross an 18" wide stream, you could bury the culvert below grade and still handle the runoff. What kind of traffic will be crossing the culvert? Nobody has asked this question which is quite important to know what the live loading is on a shallow culvert. If you intend to drive over this with heavier equipment, trucks, tractors etc you may want to increase the depth of fill over the top as well as to use a good quality material for the fill. 12" of native and 4" of gravel as suggested may be fine for light auto traffic, assuming that your native material is decent. But will not be suitable for heavier traffic.

 

[Drumchaser]

I concur with cvg and civilperson for the most part.

36" CMP (corrigated metal pipe) is what I am picturing to be used to provide a crossing over a running stream.

RCP would be better if your loads are sizeable. I would (temp.)divert the stream (or temp. dam if poss.) place 3"-6" inch aggr., and walk it down if possible, to accomodate the btm. of the new pipe (FL) to be at or below your existing creek btm. (install pipe in existing creek bed)
The large aggr. has worked well in the past for single and multiple RCP's.

I would not expect you to encounter Environmental issues (USACE, regulatory agencies, or otherwise) unless you are performimg this work for someone other than a private individual. You should however stabilize (perenial vegetation) all fill materials exposed to the stream.

If you are subject to environmental scrutiny, backfill the pipe with non-erodible material (aggregate) up to a point above the area(s) that are in contact with the stream then begin normal fill operations. The stream is considered waters of the US, however regulatory agencies (at least around here) do not "usually" approach folks on their own property.
Sounds like you are in a rural area.
Sloped ends are nice additions to this type of crossing.

Happy Trails

 

[fattdad]

Your environmental exposure has more to do with any downstream neighbors that may notice turbidity in their portion of the stream during this work. If they react (i.e., call the regulator), you will have an issue on your hands. It doesn't matter whether you are working on your land or not!

I don't make the laws, but they can bother a project like this just as easily as a big commercial job.

f-d

¡papá gordo ain’t no madre flaca!

 

[rogerrogers]

Thanks everyone for your responses. Much appreciated!

We are in a rural area and have looked into the rules re: stream crossings. It seems that agricultural purposes end up incurring much more lenient rules than residential, so hopefully we will be ok by the law.

Re: the crossing weight. Most of the time the culvert will be crossed with pickup trucks and tractors, however, we are hoping to also be able to cross with excavators, which can get very heavy; though this would be rare. We’ve already purchased the pipe and put it in the streambed, but have not backfilled yet. Is the combination of our crossing load requirements and metal pipe not feasible? Must we use concrete pipe? Can we mitigate the weight issue by adding more fill on top? What sort of material should be used for backfill/over the top in order to provide the most strength?

Thanks again.

 

[Hoagie]

Fattdad mentioned that USACE will need to be involved, I believe the permit you need is a Nationwide #39.

Regarding mitigation, if the creek is considered habitat or supports fish life, you may want to consider adding a course of streambed material along the flow line of the culvert. This will require to oversize the culvert and install it deeper so you can match the existing flowline. Contact your local fish-and-game office to learn more.

 

[rogerrogers]

Thanks for the feedback re: permits. We are looking into this more on your advice.

 

[cvg]

there is nothing wrong with corrugated metal pipe, even for large equipment. however, you will need to make sure you do a good job compacting around the haunches of the pipe, use a good quality structural backfill (not the muck that you pulled out of the stream), and then additional fill over the top of the culvert to spread the load better. Expect that the culvert may deflect when you cross it with the larger vehicles. For backfill and fill material, I would use DOT grade, crushed aggregate road base material.

 

[rogerrogers]

cvg: By "good quality structural backfill", do you mean we need to use crushed aggregate, or good quality soil? We had planned to transfer soil from an area nearby, but that is in good shape (not marshy/muddy soil). I thought that the fill, near the haunches, should not be crushed aggregate (though that had been my first idea)?

We do plan to put a good top layer of crushed aggregate.

 

[cvg]

I don't know what your soil conditions are, maybe your native soils are good. But native soils are rarely as good as road base which is probably what I would specify if I was designing this culvert for one of my clients. For additional strength with heavy loads, I would use a flowable concrete backfill. For flexible pipe installation such as your steel pipe, the backfill and compaction is an essential part of the installation. If you skimp on this, you may eventually need to replace the pipe when it fails.

 

[rogerrogers]

Could you describe what good soil would be? We have two kinds, a red, clay-like, soil, and a brown topsoil. We were planning to use the red soil.

 

[rogerrogers]

If we go with road base, should we use it all the way up the culvert, from the current streambed level, or start higher up the culvert's side?

Thanks again for your feedback.

 

[civilperson]

Either of your soil types will work if placed in thin level layers and compacted. Use 4-6" lifts and ram with the end of a two by four or rent a jumping jack tamper. The portion of the pipe resting on the grade needs support so excavate the trench to match the bottom third of the pipe. Keep the moisture of the fill damp enough to hold in a clump after squeezing.

 

[cvg]

try this for some basic information.

http://www.contech-cpi.com/media/assets/asset/file_name/3797/Installation_Manual_NCSPA.pdf