Effect of compost incorporation on infiltration capacity and erosion from a decomposed granite road cut

ABSTRACT:

Unscreened yard waste compost was incorporated into a decomposed granite road cut in the northern California coast range to evaluate its influence on infiltration capacity. A rainfall simulator was used to determine differences in infiltration capacity between treatments one year after slope construction. Infiltration capacity was evaluated using the Green-Ampt, Philip, and Holtan infiltration models. Surface saturated hydraulic conductivity was significantly greater in the compost treatment than in the control treatment (45.6 vs. 33.2 mm hr⁻¹ [1.8 vs. 1.3 in hr⁻¹]). Incorporated compost reduced the amount of settling in the top 15 cm (6 in), where penetrometer resistance in the compost treatment was nearly half that of the control treatment. Estimates of infiltration capacity, based on the Holtan model, indicate that the control treatment would generate over two times more sediment than the compost treatment during a range of design storm events. Quantifying increases in infiltration capacity on decomposed granite road cuts caused by soil amendments will act to improve compliance with sediment loss thresholds set by regulatory agencies.