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Temporary Stream Crossing

Temporary Stream Crossing

Temporary Stream Crossing

(OP)
I work for a firm that primarily does sanitary sewer rehab studies.  In our most recent project, the contractor put in a temporary stream crossing that consisted of a CR-6 (crusher run) culvert and corrugated metal pipe, as per the Maryland Sediment and Erosion Control Design Manual.  To make a long story short, we had an unusually large rainfall and the culvert was washed out.  So now we're evaluating alternative stream crossings and we had a couple of ideas.

A little background about the stream:  approximately 30 to 40 feet wide, slow flowing, about 12-18" deep under dry weather conditions, rocky or sandy bottom.

Several ideas have been floated for a new crossing:

1.  Bailey bridge (expensive, lack of contractor experience)
2.  Concrete box culverts overlaid with wood construction mats (access issues with the crane required to set the boxes, expense)
3.  Stone culvert constructed with gabion mats and corrugated or concrete pipe

The culvert has to stay in place for 2 months so that work can continue during an instream construction prohibition due to the trout spawning season.  Basically we're looking for a solution that's cheap, low maintenance, and requires minimal structural engineering (none of us are).  Just thought I'd see if anyone else had success with a stream crossing.  Thanks.

RE: Temporary Stream Crossing

Another option to consider is using a railroad flat car, if available.  I've read about somewhere in New England that one was incorporated into a permanent bridge structure, and worked on a project that used one for a temporary crossing while replacing a culvert.  

RE: Temporary Stream Crossing

(OP)
We looked at using a flatbed railcar.  Several things led us to discount it.  First, the sheer weight would require a very large crane to place it and we're not sure the construction road (CR-6 on top of geogrid) would be able to handle it.  Secondly, it's not easily removable so it would seem to lend itself more towards a semi permanent replacement rather than for our needs (~2-3 months).  That said, I would love it if we could have used it, it was cheaper than buying a Bailey bridge and it seemed like a creative solution.

RE: Temporary Stream Crossing

Did the culvert wash out due to a severe restriction in the width of the stream flow channel or inadequate protection (rip rap, geo cloth) of the culvert inlets/outlets to ensure against washout or a diversion of the original stream?  Two months is not a long time and the cost of temporary bridges would be huge.  Then again, so would culverts.

In my experience, I have usually elected (or been forced) to work outside of spawning seasons or habitat restrictions (in reference to seasonal restrictions).  

Are you laying pipe and crossing the stream?  If so, it would cheaper and less headaches (maybe less headaches only) if the pipe was augered, directionally drilled or tunneled under the stream.  That's the plan "B" I have incorporated too.

KRS Services
www.krs-services.com

RE: Temporary Stream Crossing

Most projects I work on, the Contractor is required to protect himself and the work in progress.  The design Engineer doesn't advise the Contractor on how to do this, as that just shifts the liability back on the designer.  I would guess that a analysis of the previous failure will indicate that the culvert was undersized (Contractor was trying to save money).  Contract language could be written to require a minimum size culvert and review of the contractors' plan by the Engineer.  This will help to ensure that all bidders consider the issue in preparing a bid.  Than make sure that the Contractor is fully responsible for any consequences of flooding.

RE: Temporary Stream Crossing

cvg,

Up here, due to regulatory requirements regarding working within a habitable (fish bearing) stream the contractor does not specifiy any mehodology whatsoever.  The engineer must provide a specified temporary crossing and remedial measures once completed.  This design and methodology is then reviewed and approved by the governing authority and then put into the contract for tender.

Failing to do this could result in, and I'm not kidding, arrests and steep fines for the Owner (which could be a Provincial government) the engineer and the contractor.

If a blowout has already occurred, I suggest to "etd" that the contractor provide a "shop drawing" as to how they intend to deal with the stream flows, review it as the project engineer and submit for regulatory approval.  Given the concern of trout spawning, I suspect the regulatory authority has already raised the flags about working in the stream.  Getting their approval will go a long way to a hassle free project, both from a project perspective and public viewpoint (environmental weenies).  As I mentioned earlier, if it is possible to not disturb the stream bed any further, I would explore that first as an option.

KRS Services
www.krs-services.com

RE: Temporary Stream Crossing

I'd go with box culverts. they are fairly cheap to get and you don't have to seal them because you are running the stream through them. Grade the bottom of the stream. You may have to put a silt fence across the stream to catch the stirred up silts. Lay 4 4 foot by 8 foot boxes on the 8 foot side for your 'bridge'. you will need  eight boxes to do the job. You can have the box culvert supplier run the numbers to see if standard design will hold up your vehicles for the short term. Ramp up some crushed to get to the top of the box, lay some 2x lumber on the boxes and go.  I would try to sell, donate the boxes in place to the owner so you don't have to remove them. One crane can set all the boxes if they can get right up to the stream.

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