Determining wildfire ash saturated hydraulic conductivity and sorptivity with laboratory and field methods

• Air permeametry is a viable method for obtaining initial ash Ksat.
• A sorptivity probe is a viable method for obtaining ash sorptivity.
• Ash sorptivity is a driving factor in the initial hydrological response of ash.

Post-fire landscapes are often blanketed with a layer of ash that is capable of altering post-fire infiltration response. Documentation of ash layer characteristics, specifically ash sorptivity and hydraulic conductivity, is instrumental to understanding and modeling post-fire environments and infiltration response. The aim of this study was to evaluate laboratory methodologies for determining ash hydraulic conductivity and sorptivity based on established methodologies from soil measurements. A series of field and laboratory tests were conducted on ash from 13 high severity wildfires within western North America to evaluate; i) a non-destructive method for the rapid assessment of saturated hydraulic conductivity in the laboratory, ii) a method for directly measuring ash sorptivity in the laboratory and iii) compare these laboratory methods, conducted on disturbed samples, to field measurements taken in-situ.The air permeametry method and the use of a sorptivity probe are viable methodologies for obtaining ash saturated hydraulic conductivity and sorptivity values respectively in the laboratory. Air permeametry was non-destructive, allowing ash samples to be further processed, while the sorptivity probe provided a direct measurement of sorptivity as values were collected with no gravitational component. Results were consistent between laboratory- and field-based methodologies, indicating that disturbed laboratory readings are a viable substitute for in-situ field measurements when pertaining to ash sorptivity and hydraulic conductivity. Both methodologies provide fundamental information regarding ash characteristics, which can be incorporated into modeling systems to aid in predicting post-fire infiltration response.