Paper No. 3
Presentation Time: 8:30 AM


SANTI, Paul, Department of Geology & Geological Engineering, Colorado School of Mines, Golden, CO 80401 and DEGRAFF, Jerome V., USDA Forest Service, 1600 Tollhouse Rd, Clovis, CA 93611,

Wildfires impart drastic, temporary changes on the landscape that enhance debris-flow potential. Some of these include increased erosive capacity due to shallow root loss and removal of protective litter and duff, increased runoff accompanied by decreased interception and infiltration, and enhanced sediment supply and accumulation. As vegetation recovers, soil properties return to normal, and excess loose sediment is flushed through the system, the landscape returns to pre-fire conditions. These changes are measurable, to some degree, by factors related to debris-flow occurrence. First, research has demonstrated that debris flows have higher volumes after wildfire, when controlled for variables such as basin area, and the return to pre-fire volumes typically takes 1-3 years. Threshold rainfall amounts to initiate debris flows are lower following wildfire, and the limited data available shows recovery towards pre-fire thresholds after 1-2 growing seasons, although data for longer recovery times is sparse. Finally, there is a wealth of data on secondary parameters that relate to debris-flow occurrence, including root strength loss and recovery, changes in water infiltration rates and shallow soil storage capacity, soil loss measurements (which can be considered a surrogate for soil accumulation as source material for debris flows), and measurements of changes in percentage of bare soil exposed. The recovery times indicated by these methods can be compared to recovery times estimated by other research, and differences in these values can be shown to relate to differences in the type of landscape change under consideration.