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Alternative EC08-18-03 | 16
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Using composts, organic mulches and berms as alternatives to standard erosion control materials

"Landscape Architects can solve a lot of waste disposal problems when working on a project by utilizing/recycling the on-site green waste for mulching the landscape."

- John F. Haynes

Although there are many manufactured erosion control products on the market, most of them are quite expensive to use. There is certainly a niche for them and they can be very effective in the proper application. However, with the volume of recycled green waste now available for mulches and composts, coupled with the emergence of mechanical spreading equipment, there are more reasons than ever to utilize organic by-products for immediate, cost-effective, primary erosion control.

Caltrans and the Use of Mulches

What began as an ecologically safe alternative for vegetation control was soon recognized to have other unexpected benefits. Along with providing weed control, water conservation and reduced wildfire intensity, green resource mulching also provided good erosion control. With that recognition, a special provision was developed to use mulch as a primary erosion control material.

On most projects in the past, a vegetative erosion control cover was provided at the completion of the highway construction. When a landscape was installed, that vegetative cover was removed, often at greater expense than to put it there in the first place. The contractor was required to clear the ground and keep it free of vegetation, other than what was planted, through the plant establishment period. This left much of the area subject to erosion. To reduce the erosion and herbicide applications for weed control, the policy is now that all landscape areas have to have a mulch cover.

This was made possible from two unrelated events. Previously, most of the mulch was manufactured from forest materials and applied by manual labor. With increasing concerns about capacity of landfills, legislation was passed to reduce the volume of materials going to disposal. The organic component was the easiest to divert through chipping or composting. The second factor was the development of mechanical application equipment. The current application cost of using mulch on Caltrans projects is about three to four dollars a cubic yard for the mulch, with an in place cost of fifteen to eighteen dollars a cubic yard. Five years ago the cost was double what we are paying today.

We have found that wood chip mulch can provide very effective erosion control even on very steep slopes because it serves as a buffer to absorb the force of the raindrop impact and encourage infiltration, which prevents concentrated runoff and the formation of rill erosion. It will stay in place on slopes as steep as 1:1 as long as there is no concentrated flow onto it, such as runoff from another area.

In areas where this chipped material has been placed, we noticed that rodents and birds hid nuts, acorns, and other seeds as a future food cache. Many of these seeds are not recovered though and sprout, providing free vegetation. These are often considered weeds in landscaped areas, but is actually a valuable resource for wild/native landscape erosion control.

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