Surficial Stabilization of Wildfire-Burnt Hillslopes Using Xanthan Gum and Polyacrylamide

Post-wildfire erosion and the slope instability issues associated with it are a global problem that can negatively affect transportation corridors, the environment, and human life. Currently, mulch treatments are commonly used means of stabilizing wildfire-burnt hillslopes; however, mulch, especially agricultural straw mulch, can pose environmental concerns related to invasive plants. An environmentally friendly treatment, xanthan gum (XG), and a commercial polyacrylamide (PAM) were evaluated as alternatives for stabilizing surficial silty soil that was burnt by the 2018 Mesa Fire in central Idaho to reduce runoff-dominated erosion. Indoor rainfall experiments were conducted to simulate three wet-dry cycles. Runoff and infiltration were measured after each wetting and drying event, and used to compare the effectiveness of the admixture. The total runoff at the end of three wetting events increased slightly, by ~ 4% for PAM and ~ 12% for XG. These results indicate that both PAM and XG decrease soil loss and infiltration, but that neither seals the soil surface completely. The soil loss during each wetting event was found to be dependent on the water content before wetting and the corresponding regime in the soil water retention curve. PAM and XG maintained the unsaturated state in soil, with water contents consistently around 30% before the second and third wetting events. This resulted in similar runoffs and statistically significant reductions in soil loss. At the end of three events, the soil loss was reduced by 2.9 times for XG and 6.9 times for PAM, compared to the soil loss from untreated soil.