UC San Diego

Wildfire frequency has recently increased due to climate change and anthropogenic factors, carrying along post-wildfire mud and debris flow risk. Burned scars with hydrophobic topsoil layers and without vegetation erode rapidly in rain, carrying large boulders and debris downhill. Recently, improved remediation techniques using biopolymers have been proposed for temporary protection of burned scars against erosion, until recovery and vegetation regrowth. This thesis investigates experimentally the advantages and limitations of xanthan gum (XG) biopolymer slope improvement. Among several different XG application techniques investigated, the best results against erosion were achieved with a pluviated XG and hydrophilic sand mix, cured by water spraying. For example, a 15-min 50 mm/hr rain led to a catastrophic erosion of the uncured XG mix, while the cured 1-3% XG mix protected slopes. Results showed that sand type is a governing parameter and fine sands require high XG content for soil improvement, unlike coarse sands. Results also identified surface morphology evolution, with ridges, that can fail during prolonged rain. Concurrently, six slopes with all three sand types at two different angles were exposed to natural environments and nine rain events. Initial treatments of uncured 0.5% XG mixed with sand did not reduce erosion, forming deep channels in the slopes by the fifth rain event. Re-covering the slopes with a 3% XG-sand mix and curing performed better at higher rain intensities but experienced heightened erosion in channels. Recommendations and guidelines are given for optimal XG use across different sand types, rain intensities, and slope angles.