The Effectiveness of Aerial Hydromulch as an Erosion Control Treatment in Burned Chaparral Watersheds, Southern California.

Wohlgemuth, P.M.; Beyers, J.L.; Robichaud, P.R. 2011. The Effectiveness of Aerial Hydromulch as an Erosion Control Treatment in Burned Chaparral Watersheds, Southern California. The Fourth Interagency Conference on Research in the Watersheds. 26-30 September 2011, Fairbanks, AK. 6 p.

Keywords: wildfire, erosion control, hydromulch

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Abstract: High severity wildfire can make watersheds susceptible to accelerated erosion that may impede resource recovery and threaten life, property, and infrastructure in downstream human communities. Land managers often use mitigation measures on the burned hillside slopes to control post-fire sediment fluxes as the first step in ecosystem restoration and to protect human developments. Aerial hydromulch, a slurry of paper or wood fiber that dries to a permeable crust, is a relatively new erosion control treatment that has not been rigorously field tested in wildland settings. Concerns have been raised over the ability of aerial hydromulch to reduce watershed erosion along with its potential for negative impacts on post-fire ecosystem recovery. Since 2007 we have measured sediment fluxes and vegetation development on plots treated operationally with aerial hydromulch and compared them to untreated controls after three separate wildfires in southern California. These study plots, located on steep slopes with coarse upland soils previously covered with mixed chaparral, were monitored with silt fences to trap eroded sediment and meter-square quadrats to measure ground and vegetation cover. We found that aerial hydromulch did reduce bare ground on the treated plots and that some of this cover persisted through the first post-fire winter rainy season. Aerial hydromulch reduced hillslope erosion from small and medium rainstorms, but not during an extreme high intensity rain event. Hydromulch had no effect on regrowing plant cover, shrub seedling density, or species richness. Thus, in chaparral watersheds, aerial hydromulch appears to be an effective post-fire erosion control measure that is environmentally benign.

Moscow FSL publication no. 2011l