Post-wildfire soil hydrophobicity and slope erosion remediation by applying environmentally friendly modifiers

This paper investigates the use of environmentally friendly remediation materials and techniques for rain-induced post-wildfire soil erosion on burned slopes. During wildfires, vegetation and organic matter combust and release hydrophobic chemicals on soil grains. Hydrophobicity reduces the water infiltration rate, prolongs the wetting process, increases erosion, and causes severe debris flows over watersheds. This comparative study presents the most effective approaches for mitigating hydrophobicity effects through environmentally friendly biopolymers and surfactants. Experimental techniques evaluate the dynamics of water drop penetration into treated and untreated soil, downhill water drop mobility, and erosion. The waterdrop contact angle measurements indicate that biopolymer Xanthan Gum (XG) slightly reduces hydrophobicity, whereas surfactant Sodium Cocoyl Isethionate (SCI) reduces it by a factor of a thousand. In addition, SCI can decrease slope erosion at low-inclined and moderate-inclined slopes. Sands' infiltration rates (IR) are very fast due to high permeability in normal conditions; however, surface hydrophobicity significantly reduces IR. Results from artificially treated extremely water-repellent samples of mixed sand show a six orders of magnitude decrease in IR. Then, after treatments XG and SCI modifiers, the IR increased by an order of magnitude after the XG treatments, and by four orders of magnitude under SCI treatment. Although XG is wettable and attractive to water, the crust and webs it forms between sand particles prevent effective water infiltration. Mild slopes exhibit similar IR rates as horizontal surfaces for all the cases; however, steeper slopes reduce IR for treated hydrophobic soils because they allow for downhill motion of water that is faster relative to the infiltration speed.