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Silt Fence That Works is a comprehensive four-color manual about the proper design and installation of silt fence. Millions of tons of sediment leave construction sites each year because of improper design and the installation of silt fence. Millions of dollars are spent on these ineffective controls. Many designers and contractors have not been trained in sediment control. This manual details the what, where, when, why, and how of effective silt fence, and discusses the latest technology available. The old specifications simply do not work to control sediment. By using pictures and graphics to show both bad and good practices, to explain proper design including quantity issues, and to demonstrate new installation technology, this manual offers a system for constructing silt fence that actually holds water, allowing sedimentation to occur.
available, Silt Fence That Works condensed installation
guide and a power point training program.
Below are four exerpts from Silt Fence That Works:
The specifications were written 25 years ago and have changed little since then. Some states have recognized some of the inherent problems, such as inadequate trench depth, and implemented minor changes to improve efficacy.
Many states simply pay millions of dollars and receive little control because installers and inspectors don't know how silt fence works, where to place it, how much is needed, and no one cares.
The 25 year-old specifications, referred to as the trenching method, have never been tested for efficacy and proven worthwhile. A trencher was simply the only piece of equipment available at the time capable of securing fabric in the soil, regardless of efficacy. Today many contractors just open a furrow with a blade and backfill onto the fabric with the crumbs.
When you have two slopes, the flattest slope is the valley and the steeper slope becomes one side of your dam. To create a pond, you must create the dam and one other side. The fastest and most efficient way to do this is to build a silt fence creating the dam and required third side.
The common perception that you have only to worry about water off a steep slope is incorrect. Yes, slope contributes to velocity, which is harmful, but a steep slope may not have a large collection area, and therefore, may not have much water to contend with.
If you get a one-inch rain over one acre in 2 hours you will have erosion, regardless of slope. If there is only a half percent slope over one acre, non-absorbed water will concentrate and start eroding the soil somewhere as it seeks the lowest area.
Slope will contribute to velocity, which increases the rate of erosion, but the total drainage area is more important in determining sediment loss. As the volume of water concentrates, its weight and velocity will increase, as will the erosion of soil.
Once a fence is full, the value of cleaning it out is questionable. At this stage, the fence is plugged with silt, so the water will not seep out of it as it is supposed to. Scooping a few buckets of sediment away from the backside of the fence effectively makes the area a limited capacity sediment basin, which generally stays full of water, etc., and therefore useless, and the disposal problem for sediment still exists.
A new fence in front of or below the existing silt fence seems to make sense — you gain an empty storage area, the previous sediment is still contained, and the new fence should slowly release water as designed. But there may not be room for a new fence. Decisions and adjustments must be determined on a site by site basis. Blind rules are not applicable to many erosion and sediment problems on construction sites.
Inspectors must know how silt fence works, how to decide where to install it, how to install it properly, how much to install, and how to tell if it's working. Cosmetic silt fence is no longer an option. Allowing and approving cosmetic silt fence for payment is no longer an option. The law, the environment, the landowner/developer, and the neighbors demand erosion and sediment control measures that work!