This is not one of my projects but we have used this method on occasion. Why install silt fence when you can create a sod berm perimeter BMP?
In this case, the area is small and it is surrounded by vegetation so the risk of erosion and turbid runoff is low. In addition, the sod is full roots and seeds so it will regrow in place, providing additional erosion prevention.
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.
Sorry to say, but this is really stupid. All of the cost to repair these was on the contractor and included placing additional soil amendment, re-grading and re-spraying bonded fiber matrix, seed and fertilizer.
With limited time to close and demolish over one and half miles of concrete runway, add new utilities, lay asphalt, pour concrete, groove, stripe, and flight test, we had to hydroseed (bonded fiber matrix) as soon as an area was completed. The plan was to have at least 85% grass cover going into fall and winter. Water trucks were fitted with used adjustable fire nozzles purchased on Craigslist; the original nozzles on the trucks were for flushing, not watering grass. We managed to exceed the goal of 85% cover on about 90% of the project. We hydro-seeded the rest of the areas in early winter knowing the grass wouldn’t grow. Fortunately, we had modified the storm system to collect any turbid runoff from the areas not stabilized and treat it with Chitosan-enhanced Sand Filtration systems.
More Grass Equals Cleaner Water – The Clean Water Act requires construction sites to meet water quality standards. One of the standards is turbidity, the measure of the cloudiness of water. Turbidity is measured in NTUs, nephelometric turbidity units, using a turbidity meter. The turbidity meter shines light through a water sample and measures the light intensity difference between the light emitter and collector; the cloudier the water, the higher the NTUs. The chief cause of turbidity in construction stormwater runoff is fine soil particles; fine silts and smaller. Persistent turbidity is caused by colloidal soil, particles which are so small the soil particle’s negative electrical charge is stronger than the force of gravity. This causes the particles to remain in the water column for long periods of time. Particles of this size do not settle out. The best way to keep the colloidal particles from entering stormwater is to protect the soil surface, both from the force of raindrop impact, as well as the shear stress of flowing water. Vegetation is the single best way to protect bare soil from these forces; the more vegetative cover the better. In this video, the affect of grass cover is apparent. Turbidity samples, taken from runoff from a grassy area with 70 to 80 percent soil cover is under 25 NTUs, the allowable discharge number.
This video discusses ways to enhance grass growth.
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.
This is one way you can check the grass and mulch cover percentage using Line Intercept Sampling.
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