Highway construction has historically been viewed as a major contributor of non-point source pollution. Non-point source pollution - or pollution such as surface runoff that cannot be linked to a particular source - is cited as being the most prevalent cause of contamination in receiving waters in the United States.
Damage control for erosion at construction sites can include erosion control nets, open-weave geo-textiles, geo-synthetic mattings, erosion control blankets, loose mulches, hydro mulches, and chemical soil binders. Most are designed to absorb the kinetic energy of rainfall by minimizing its contact with the soil and reducing water velocity. The performance of common sediment control methods such as fences, straw bales, and sediment ponds depends on the quantity of site erosion and maintenance.
The Texas Transportation Institute (TTI) conducted study 0-1352, "The Use of Compost and Shredded Wood on Rights-of-Way," for TxDOT, the Texas Commission on Environmental Quality (TCEQ), and the Federal Highway Administration (FHWA). The purpose of the study was to determine the performance of compost and shredded wood as erosion control materials for use on highway rights-of-way based on literature reviews and field tests.
The application of mulch - either compost or shredded wood - appears to be an effective erosion control method, and the mulch does not need to be removed after construction. Left in place, the mulch can provide a soil amendment to encourage the establishment of vegetation. Compost may also chemically bind some toxic substances, which suggests that it may have some application in bioremediation.
Several research groups have demonstrated the potential of compost as an erosion control material. Compost, in a sufficiently dense mat can provide a physical barrier between rainfall and surface soil, dissipating the impact energy of rainfall and minimizing erosive forces.
TTI tested three materials in six test plots. The test materials were:
There were three sand plots and three clay plots, on a 1:3 slope in a simulated highway environment. Rain simulations for 1-year, 2-year, and 5-year storm events tested for sediment loss on the plots. The percentage of vegetative cover was captured using the Vegetation Coverage Analysis Program.
|Type of Plot||Vegetation Cover||Sediment Loss(kg/10m5)|
|Compost on Sand||92%||3.88|
|Compost on Clay||99%||.34|
|Wood Chips w/Terra TackJ SC on Sand||48%||11.27|
|Wood Chips w/Terra TackJ SC on Clay||95%||.15|
|Wood Chips w/RMB Plus on Sand||50%||10.97|
|Wood Chips w/RMB Plus on Clay||57%||.30|
The compost produced 92 percent vegetation cover on sand and 99 percent vegetation cover on clay. The test plots lost 3.88 kg/10m5 of sediment on the sand plots and 0.34 kg/10m5 on the clay plots. Wood chips with TERRA TACKJ SC produced only 48 percent cover on sand while producing 95 percent vegetation cover on clay. These plots lost sediment at a rate of 11.27 kg/10m5 on sand and 0.15 kg/10m5 on clay. Wood chips with RMB Plus produced only a 57 percent vegetation cover on clay and a 50% vegetation cover on sand. The plots lost sediment at a rate of 10.97 kg/10m5 on sand and 0.30 kg/10m5 on clay.
The results obtained for compost met the minimum performance standards required by TxDOT for soil retention blankets. Wood chips with TERRA TACKJ SC would qualify as a material for use on clay with slopes of 3:1 or less. The wood chips with RMB Plus did not meet any TxDOT standard.
Test results exceeded expectations and are most encouraging. Debris from right-of-way clearing operations may provide a cost-effective source of wood chips.
The contents of this summary are reported in detail in TTI Research Report 1352-2F, The Use of Compost and Shredded Wood on Rights-of-Way for Erosion Control, Beverly B. Storey, Jett A. McFalls and Sally H. Godfrey, preliminary report dated November 1995. This summary does not necessarily reflect the official views of the FHWA, TNRCC or TxDOT.