Effective Infiltration Measurements for Fire-Affected Water-Repellent Soils

One of the notable effects of wildfire is the water-repellent condition of fire-affected soils. The resultant attenuated infiltration can contribute to the increased flooding and erosion often associated with subsequent rainfall events on burn sites. Recently, we have developed a physically-based model describing how the degree of water repellency is associated with the soil property of sorptivity, and how altered sorptivity affects infiltration. Using measurements from upward infiltration (wicking) experiments, water drop penetration time (WDPT) tests, and tension infiltrometers on artificially-treated sand with varying degrees of water repellency, we found the effect of soil water repellency on infiltration is highly non-linear and significant even for "slight" degrees of repellency. While techniques for assessing the degree of soil water repellency are many and varied, sorptivity is seldom measured, however, and standard infiltrometer methods appear inadequate. The objective of the research is to assess and identify accurate, efficient, and simple methods needed to assess soil water repellency for effective predictions of post-fire runoff.