Stream Crossing Design (NY NRCS Standard 578)
We'll be looking at the 3 types of stream crossings: at grade (fords), culverts, and bridges. Each type has trade-offs in price, design complexity, pollution prevention, wildlife impact, and stream morphology impact. We'll cover the pros and cons you should consider during the design process so you can make good decisions when crossing streams on your farm projects.
Introduction and Background material
EFH2: Skim through the chapter, then download the software and try to run through some scenarios. Here's the link to the install file: http://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/national/water/?cid=stelprdb1042480 Additional Instructions for NY users are here (bottom of page): http://www.nrcs.usda.gov/wps/portal/nrcs/main/ny/technical/engineering/
TR-55: TR-55 expands on the topics of EFH2 and gives methods for analyzing urban watersheds. It's biggest advancement is computing the time of concentration for a watershed using a multi-segment flow path.
ESI Manual: This is a great introductory reference to stream geomorphology. The manual is geared towards emergency stream intervention following flooding, so it doesn't get into the really fine details about stream corridor management and restoration. That's why it's a great resource if you're taking this course.
A quick look at shear stress in streams and channels.
To compute the shear stress you'll need flow depth. To compute your flow depth you'll need the channel cross section and slope (from land surveying) plus the 10-year discharge (from EFH2). This lecture shows how to combine this data to get the design storm flow depth. Here's the link to download HEC-RAS: http://www.hec.usace.army.mil/software/hec-ras/downloads.aspx
Shear Stress: This research paper from the Ecosystem Management and Restoration Research Program (EMRRP), a division of the Army Corp of Engineers, is a great overview of shear stress in natural stream channels.
A look at how fencing should be handled at at-grade crossings.
Types of Stream Crossings
The is a PDF of the NRCS Standard 578 Stream Crossings. You need to read it carefully. There is a test on it. I'm not joking.
Cattle slats are a great low-maintenance option for at-grade stream crossings. They're pricey, but I think they're worth it!
***Update: Cutoff walls at the upstream and downstream edges of concrete ford crossings are mandatory as of 2012 - they're no longer optional. The cutoff walls should be 6 inches thick, 18 inches deep into the streambed, and extend up the banks to the bankful elevation. Can be either rock or concrete.***
NRCS Flyer: This is such a nice little flyer I just had to include it. It's from NRCS national.
A look at rock at-grade crossings with and without cellular confinement.
A look at some of the installation issues for culvert stream crossings, intended to complement the "Culvert Design Using HY-8" Udemy course.
VT Stream Crossings: Although not apparent from the title, this handbook focuses on culvert design for effective AOP in streams, and covers the basic biological mobility needs of aquatic animals.
MD Culvert Design Guide: This is a great reference on culvert crossings on farms, and goes into basic hyraulics as well. Still, you should use HY-8 for the hydraulic design instead of the nomographs presented here.
Unfortunately NY State education law won't allow you to sign off on a bridge without a Professional Engineer's license, but that doesn't mean you shouldn't consider them. Let's check out a couple that NRCS has built, one in NY and one in MD.
MD Design Guide: If you're thinking about proposing an agricultural bridge, start with this design guide. You will still need a site-specific design and a Professional Engineer to complete the design work, but this will get you headed in the right direction.
This is an introduction on the stream crossing site that we'll use as our design example. The instructions and sample deliverables are included in the next lecture. If you get stuck feel free to contact me via the course message board or email (firstname.lastname@example.org)
Here are the instructions for completing the course project. In it you will need to complete hydrologic and hydraulic computations for a simple cross section, sketch a basic design return it to me. You packet that you hand in should look like the one I've supplied as a supplement to this lecture.