Environmental Effects of Applying Composted Organics to New Highway Embankments: Part 2. Water Quality Part 3. Rill Erosion

Abstract

<p>Control of stormwater runoff and soil erosion on highway construction sites is a concern for state departments of transportation and municipalities. Composted organics are viewed as an alternative approach to improve construction site soils and to reduce runoff and soil erosion. The objective of this study is to evaluate the use of blanket-applied composted organics on rill erosion as compared to soils. Rill erosion was measured on three composted organics applied at 5 and 10 cm depths, a topsoil treatment (15 cm application), and the existing soil (control) on a highway embankment with a three-to-one sideslope (33%). Treatments were tested using rainfall simulation at a target rate of 100 mm/h and simultaneously adding five inflows at the top of the rill on both vegetated and unvegetated plots. Rill erosion on blanket-applied compost treatments was measured, and the usefulness of the shear stress model for predicting rill erosion on compost-treated areas was assessed. Rill erodibilities and critical shear values were calculated for all treatments using the shear stress model that was originally developed for soil. Rill erodibilities were higher on topsoil-treated plots than on control and compost-treated areas. Yard waste had significantly lower rill erodibility than all other compost and soil treatments. There were no significant differences between critical shear values for the composts and soil. Yard waste compost exhibited greater resistance to rill formation than the biosolids and bio-industrial composts or the two soils. Low R2 values for compost erodibility and critical shear suggest that the shear stress model used in this analysis is not well suited for use with composted organics. Detachment caused by flotation of low-density particles, and bridging caused by coarse particles lodging farther down the slope, are believed to be two rill erosion mechanisms in compost that the shear stress model does not adequately address.</p>