We used to use silt fence when we did construction on the airfield. More and more we are using compost berms. The airfield grades are very small, maybe 20:1.
Compost berms can contain bare soil areas, filtering turbid water. When complete, we spread the compost and hydroseeded.
We rarely use silt fence on smaller airfield projects because: the work areas are nearly flat, are surrounded by grass or pavement, the work takes a few months, usually in the summer or fall. Compost berms are frequently used to: contain water, divert water, prevent site runoff. A secondary benefit is filtration; there is some turbidity reduction. Lastly, when done,. we spread the compost out over the disturbed soil and hydroseed it, enhancing grass growth and eliminating the waste of land-filling silt fence.
In this video, I show a compost berm, or sock, and how it is used to protect a catch basin.
This compost sock catch basin berm works well as it is heavy enough to stick to the asphalt. Note the tear and I would keep an eye on it during inspections.
As I have written in previous posts, compost socks make excellent perimeter berms, especially when used on impervious surfaces. Make sure to overlap the ends and don’t drive over them. Recycle the compost when done.
This would not have been my choice as a berm for quarry spalls; straw wattles are too light to use on asphalt and they allow water to flow under them. A compost sock, being heavy, would work better, though, they are prone to tearing. An asphalt berm might be best here.
Install Compost socks with an overlap on each end to maintain a continuous berm. 8 to 12 inches works well. Consider this when figuring out how many you need to order.
The bulk of the work will take place to the right of the silt fence. The grass will be removed and the area re-graded. The grass to the right of the construction fence will remain undisturbed. Some work will occur on the taxiway to the left of the tractor. Rather than use silt fence in this low risk area, compost berm will suffice. When done, the construction fence and stakes will be removed and re-used elsewhere and the compost will be spread out on the grass.
Let’s talk about grass and dirt berms. Most erosion plans show silt fence installed around the project perimeter. This makes sense when a project has some risk of eroded sediment leaving the project.
When the risk is low, the area is small, the soil is loose with high infiltration, silt fence is overkill, wasted expense, and creates landfill waste. When possible, alternative methods of perimeter protection should be considered: berms, straw wattles, vegetation, buffers.
We pushed existing grass and vegetation to the edge of the project and covered it with straw. The project involved tilling compost 12″ into the native soil with a 12″ bark cover.
The seed and root mass in the soil will grow fairly quickly and become part of the overall native plant mitigation area.
I was just minding my own business last Friday, driving from Fred Meyer to the UPS store and passed this project. I told my wife I have to get a photo; she says okay since she knows me and my habit of stopping to take TESC photos.
I made a u -turn at the Wal Mart, drove back a block and stopped in the middle of the street to get this shot.
There is so much wrong here, where do I start? Clearly, dirt is tracked off of the project in the background, as you can see the sediment build up in the curb line. Someone told someone to put something in the swale to keep dirt out, then someone else installed this silt fence.
First off, silt fence needs to be trenched in and this just has a few rocks placed on the flap.
Second, they probably couldn’t trench this in anyway without tearing up the drainage swale.
Third, only two of the three curb cuts are backed by the silt fence.
Fourth, silt fence is a barrier, not a filter, and with the volume of water draining off the asphalt during a rain event, dirty water would just blow around and under the silt fence.
Conclusion, silt fence is never used in a water flow situation; it is only to contain eroded sediment from a sloped area. A better BMP here is a compost berm or something similar that would allow some water to pass but filter some sediment. Sand bags would work to keep everything out of the swale but then the dirty water would bypass to the next catch basin, which probably has a catch basin insert, which would collect sand and such but would not do anything for turbidity. So, what is the best BMP? Stop the !@#$ ing trackout in the first place!
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