Preventing erosion is essential to maintaining the quality and productivity of the soil and protecting the health of the nearby waterways.
Erosion due to roadway projects often occurs because, at the beginning of construction, vegetation and topsoil is removed, leaving behind soil too poor to sustain good plant growth. If not treated, the eroded topsoil, which may contain fertilizers or other toxic material, is washed away — likely into nearby waterways.
The problem can be prevented by surrounding the pavement, and often adjacent steep slopes, with vegetation. However, if the plant life does not take root immediately, the soil will wash away and plant growth will become extremely difficult.
Traditionally topsoil, seeding and erosion control blankets have been used to control erosion; however, these methods often require repeated attempts and become timely, costly and unsuccessful in poor soil conditions.
Since the 1990s, incorporation of green landscaping or greenscaping methods, including the use of compost in controlling erosion, have been incorporated into highway project designs. To encourage these methods, the U.S. Environmental Protection Agency (EPA) created GreenScapes, which promotes practices and products in landscaping that are environmentally friendly.
According to Jean Schwab, GreenScapes program manager, in recent years, a “Compost Use On State Highway Applications” publication was developed between the EPA, the United States Composting Council Research Education Foundation (CCREF) and the United States Composting Council (USCC), to promote the use of compost along state and local roads and highways.
“Numerous studies throughout the country have shown that compost supplies nutrients, retains moisture, and helps establish vegetation on harsh growing sites where traditional erosion control methods have failed,” Schwab said.
Compost is a product resulting from the controlled biological decomposition of organic materials, primarily yard debris, food scraps and sometimes manure, that is sanitized through the generation of heat and stabilized to the point that it benefits plant growth. Therefore, compost can improve or reclaim damaged or nutrient-poor soil so it is capable of preventing/controlling erosion.
“Initial costs for applications of compost vary depending on the site and may or may not be slightly greater than the initial costs of traditional methods,” Schwab said. “However, when correctly applied, compost provides superior filtration and erosion prevention/control is more easily installed and maintained, and does not require-labor intensive removal or disposal from the site once the job is completed. As a result, this greatly reduces the overall costs as compared to traditional erosion control methods all while providing better and faster results.”
Case Studies
Like many states, Texas struggles with roadside erosion. In the late 1990s, The Texas Department of Transportation (TxDOT) began using compost in highway construction designs. Texas is now considered a leader in the use of compost along highway systems for erosion control.
According to Barrie Cogburn, director of landscape and enhancements of the design division of TxDOT, the use of compost in erosion control is gaining acceptance as more contractors and designers become aware of the benefits associated with its use.
“There are many advantages to the use of compost for erosion control,” Cogburn said. “Along with limited long-term maintenance, compost has shown to be nearly 50 percent less expensive to apply than traditional erosion control blankets.”
The blankets only protect the seedbeds, he said, while “the combination of compost and woodchips amends the soil and protects the seedbed, thus quick and stable vegetation occurs.”
Faster embankment stabilization means the contractor can move on to other phases of construction sooner, Cogburn said.
One of the first compost projects in Texas was implemented at Big Springs, a badly eroded hillside where, for approximately 30 years, multiple unsuccessful attempts at seeding, hydromulching and blanketing had failed.
“Finally, in 1997, a 50-percent mixture of compost and wood chips was applied to the slope, which, by then, was worn down to its subsurface soil. Not only did the compost remain through 40 mile per hour winds on the day of application and resist a heavy rainfall shortly after application, but two months later, the site was heavily vegetated and remains so to this day,” Cogburn said.
These results were enough to prove to Cogburn the tremendous potential of compost as erosion control.
“The more success stories that are circulated and the fact that compost is both time and cost effective will lead to it eventually becoming the method of choice.”
Recently, the Eastern Federal Lands Highway Division (EFLHD) used the composting method after a small landslide along the Blue Ridge Parkway near Asheville, NC, took out a section of the roadside cut area. The project was unprecedented in that it was the first time EFLHD had used compost in this capacity and to roadside terrain this steep.
According to Mitch King, project engineer of the EFLHD, compost is an excellent tool in erosion control, not just for its tremendous success rate, but for its additional benefit in reducing the invasion of pesky plants.
“The heat generated during the compost process eliminates the ability of weeds and other unwanted exotic plants to grow,” King said. “I have worked directly on numerous compost projects, including the one along the Blue Ridge Parkway. The results in every case indicate that compost has a bright future as an erosion control method; not only is compost as good as or better than conventional erosion control methods, but it also benefits the environment by reducing the invasion of exotic plants, which is of particular importance in environmental sensitive areas such as the Blue Ridge Parkway.”
Application of Compost
The EPA and the USCC has established that in the case of steep embankments along highway systems — no greater than a 3 to 1 slope — compost can be an effective method in reducing/controlling erosion.
Studies have found that applications of 2 in. of compost when applied — typically with a bulldozer, grading blade or pneumatic blower — is an effective method of erosion control. TxDOT recommends that erosion control compost consist of 50-percent untreated wood chips blended with 50-percent compost. To further slow runoff from receiving waters, the use of berms of compost, 1 to 2 ft. high and 3 to 4 ft. wide placed at the top and bottom of the slopes or the use of filter socks will give additional protection.
Schwab emphasized, however, that the type of compost and the method of application used, such as compost blanket, filter socks or berms is dependent on the sites conditions such as soil type, slope and regional weather conditions.
“Compost provides superior filtration and erosion prevention/control and is more easily installed and maintained,” Schwab said. “Utilization of compost along steep highway embankments not only accomplishes quick and stable plant growth but also produces significant cost savings when compared to traditional erosion control methods. Additionally, it reduces the biodegradable wastes that go to landfills —important because yard trimming and food residuals together constitute 23 percent of the U.S. municipal solid waste stream.”
Federal agencies are required to use recycled products, but Schwab believes the use of compost will be popular at all levels of construction, right down to the private contractor.
“We feel that through education, the state DOTs, the landscapers and others involved in highway and roadway designs will eventually accept and utilize compost as a common erosion control method,” Schwab said. CEG
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