distance from a creek when silt fence is not needed
distance from a creek when silt fence is not needed
(OP)
I am working on an erosion control plan for construction within a national forest. It would seem that at some point silt would dissipate before reaching a creek or stream if it is a certain distance from the construction. Could there be a rule of thumb based on the distance, slope and condition of native ground, and maybe soil type in which silt fence would not be needed?





RE: distance from a creek when silt fence is not needed
Where's the project?
If you're clearing a lot of trees and/or brush with your construction, I've seen brush barriers made of onsite vegetation work wonders here in the southeast. Sometimes those can be more effective than silt fence.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: distance from a creek when silt fence is not needed
RE: distance from a creek when silt fence is not needed
No matter what sort of back-up you find for not having silt fence now, you only have two defenses in court if someone comes after you:
1) Turbidity tests showing no increase, or
2) Proof that you followed the checklist.
If you're a Georgia PE then you know how out of whack those turbidity tests can get, due to no fault of your own or of the contractor. I know our natural tendency as engineers is to find the 'best' solution, but the best way to stay out of court in modern litigious society is often to find the 'safest' one.
When the Georgia NPDES construction permit first came out, there was a lot of language in it that made engineers criminally liable for erosion failures even if their plans met every code. Like, jail-liable. A lot of guys spent a long time campaigning for revisions so that as long as the plans were done to a particular standard, the engineer was covered. Your safest bet is to follow the standard.
Now, beyond that, your post does bring up some interesting academic / engineering questions. All erosion control design for construction I've seen personally followed sets of pretty basic design standards, such as the Georgia Green Book, which crafts its criteria in the style of "always have Type XYZ silt fence at ABC location" and "all basins bigger than PQR must have a sediment pond" etc, without actually trying to model sediment discharge itself.
South Carolina is one of the few states in the southeast I haven't done any work in, but I heard a rumor that they require a SEDCAD model for construction plans, which is the sort of thing that would calculate what you're talking about, because it's a treatment-train calculation software for sediment loading. I'm not familiar with SEDCAD personally, but if they've got a treatment efficiency listed for undisturbed buffer, and it varies with width, and you can compare the SEDCAD predicted efficiency of the buffer with the SEDCAD predicted efficiency of Type C silt fence, you're well on your way. Go through their documentation and find out where they got their numbers from, and cite that to the EPD. But you absolutely ABSOLUTELY must get a signed hardcopy letter from someone reasonably big at the EPD saying they buy your approach. Again I stress, the important thing here is having the ability to deflect liability if it comes up.
Then again, by the time you've done all that you could have done the plans to standard. I also think you'll find that regulators aren't in the business of assuming liability, so the moment you try and get them to hang their hat on a decision that departs from a design standard, they usually balk and refer you back to the standard. Regulators never get fired unless they screw up a hard decision, which means the smart ones can get infinite job security by never making any decisions. It's just an unfortunate artifact of the business model.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: distance from a creek when silt fence is not needed
RE: distance from a creek when silt fence is not needed
Cue engineers from other areas of the country replying with "what the hell do you need silt fence for on a trail anyway?" You and I will probably have to just grin and shake our heads.
Another approach you might be able to take, depending on the alignment of the trails, is to go with rock filter dams in draws downhill. That's a more natural BMP and could conceivably be left in place after construction, to some environmental benefit.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: distance from a creek when silt fence is not needed
RE: distance from a creek when silt fence is not needed
f-d
¡papá gordo ain't no madre flaca!
RE: distance from a creek when silt fence is not needed
EPD might accept that, and you might be able to lean on that legally as well, but you should be aware that the TSS spreadsheets released by northgeorgiastormwater.com, as well as the local ones for Gwinnett and Forsyth and etc/etc, aren't really based on anything I'd call "reality," and the undisturbed buffer portions are a "credit" that's been purely manufactured out of thin air as encouragement for low impact design. They're also intended to be for permanent BMPs, not temporary erosion control. They're basically the CYA document that local munis run up the flagpole to EPD, so EPD can claim compliance with the non point source provisions of the Clean Water Act.
You could easily use the things to show that you meet water quality criteria for new development, but I'm not sure you could reasonably claim to calculate sediment storage with them. Especially since the Blue Book doesn't publish TSS removal efficiencies for temporary erosion control measures.
Those things will be particularly helpful to you if you end up having to go through the stream buffer variance process for your trails. Hopefully you're exempt though, I don't have all the exemptions memorized.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: distance from a creek when silt fence is not needed
RE: distance from a creek when silt fence is not needed
http://fargo.nserl.purdue.edu/rusle2_dataweb/
I'd love to see what you come up with.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: distance from a creek when silt fence is not needed
RE: distance from a creek when silt fence is not needed
RE: distance from a creek when silt fence is not needed
As an alternative to silt fence, many jurisdictions have details for perimeter dikes for sediment control. I would proposed a very small version consisting on the scraping of the trail bed on the downslope side of the trail. I would detail this miniature version.
RE: distance from a creek when silt fence is not needed