The Effectiveness of aerial hydromulch as a post-fire erosion control treatment in southern California

Wohlgemuth, P.M.; Beyers, J.L.; Robichaud, P.R. 2010. The effectiveness of aerial hydromulch as a post-fire erosion control treatment in southern California, In: Proceedings of the Joint Federal Interagency Conference, 9th Federal Interagency Sedimentation Conference and 4th Federal Interagency Hydrologic Modeling Conference, June 27-July 1, 2010, Las Vegas, NV. 12 p.

Keywords: mulch, hydromulch

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Abstract: Following a wildfire in the Santa Ana Mountains of northeast Orange County, California, a monitoring project was established to test whether aerial hydromulch reduced post-fire hillslope and small watershed erosion, and to document its impact on re-growing vegetation. The study site received below normal rainfall both the first and second winters after the fire. A high-intensity thunderstorm at the end of May 2008 produced very high peak rainfall intensities, providing an extreme test for the hydromulch. It appears that the mulch reduced hillslope erosion during low and moderate rainstorms, but not during heavy downpours. Once the hydromulch is removed, the sites are susceptible to erosion during subsequent higher intensity storms. Because the spatial differences in the rainfall were confounded with the treatment and control locations, the effect of the hydromulch on stream channel erosion is unknown. Cover assessments showed that the hydromulch did significantly reduce bare ground on the hillsides, and that this cover persisted until the time of the intense thunderstorm. Differences in pre-fire shrub composition and post-fire herbaceous species composition makes it impossible to separate the hydromulch effects from inherent site differences on plant response, suggesting that there was no treatment effect on vegetation recovery.

Moscow FSL publication no. 2010i