I know tonight is a night I should write in the blog, but I'm a little without topic write now. Today was a good day, very busy with my silt fence studies. I finally pulled up a blank specification template and actually began writing the specification for silt fence. I found it to be a little more difficult than I expected. When I got to the part of entering what types of silt fence fabric we will accept, I went to the highway department list of accepted products. I found fifteen different fabrics accepted. On our standard drawings we have four listed. So I had a lot of work to do.
I found the highway department's list terribly out of date. Or maybe full of errors. They were using some products that aren't really silt fence type fabric. They had one company down as a manufacturer when they are actually a re-seller, not even a value-added re-seller. The products they listed varied as to apparent opening size by 2.8:1, and by permittivity (a measure of flow rate) by 145:1!!!! Clearly, someone wasn't thinking when they put all these products on the list. Hmmm, one naturally suspects kickbacks in a situation like this.
But as I was trying to view manufacturer's literature, I found I would have to take a step backwards and actually do some design work before I could specify the darn thing. This is how I should have done it in the first place.
I must digress to say that on March 31st I will be presenting a paper at an erosion control conference in Bentonville (almost walking distance from the new office), the subject being "A Thousand Little Treatment Plants: Process-based Design of Erosion and Sediment Control Practices." The premise of the paper is that the industry has been treating these things as "best management practices." As management practices they are art, not science. Hence they don't get designed. Hence they don't get detailed and specified correctly. Hence they don't get selected, installed, or maintained properly.
Well, here I am writing a paper saying the industry isn't doing the right design work, and I'm trying to write a spec without first doing some design work! Ridiculous. I had done enough study to know that my spec should not allow vastly different types of fabrics in it, and to know what the key properties were that affected the design. But do I chose the small group of fabrics that have a flow rate of 5 to 10 gallons per minute per square foot, or the small group of fabrics that discharge at 100 to 150 gpm/sf? Which is the better basis for silt fence design? I don't know, but I need to in order to write the spec properly.
Or, should we be specifying two types of silt fence: low flow capacity to maximize sedimentation, and high flow capacity to minimize upstream side ponding area? Perhaps there's room for both in our specs. And maybe that would give us one more tool in our sediment control toolbox. Of course, our engineers would then have to make intelligent decisions rather than mindlessly put symbols on drawings and ignoring specifications. Wouldn't that be terrible.
So, that means we have at least four types of silt fence:
- Low flow capacity i.e. maximum sedimentation silt fence
- High flow capacity i.e. filtration only silt fence
- Wire backed silt fence, which I suppose could be either of the two
- Belted silt retention fence, which has a different type of fabric and which I've never used; it's on the list to research tomorrow.
Or maybe not. Maybe I'm breaking some new ground here. I can see reasons to apply both types of silt fence. Of course, until I sit down tomorrow and do those calculations and figure how these flow rates apply to the situation on the ground, I may be worrying about nothing. Somehow, though, I don't think I am. I think I've stumbled upon something important, and will do something that will improve the industry. Or at least CEI's part of this.
Well, for having nothing to write about when I started, I wrote quite a bit. Not of much interest for those readers who tune in ever day to see what I've written about my writing career, but it's something of interest to me at the moment, and that's what this blog's all about. Carlyle and Emerson can wait for other posts.