HR: 09:00h
AN: H51M-05    [Abstracts]
TI: The Role of Vegetative Ash in Post-Fire Erosion and the Generation of Progressively-Bulked Debris Flows
AU: * Gabet, E J
EM: egabet@email.sjsu.edu
AF: Dept. of Geology, San Jose State University, Duncan Hall, San Jose, CA 95192, United States
AB: It has been proposed that the creation and deposition of a layer of ash on the ground surface can enhance erosion by surface runoff and might even be a necessary condition for the generation of progressively bulked debris flows. We conducted flume experiments to investigate the role of ash in increasing the volume and transport capacity of runoff. We found that the presence of ash on the soil surface reduced the ability of flowing water to infiltrate; this effect was even greater when the ash had been pre-wetted. In addition, we found that the transport capacity of flowing water is enhanced by the incorporation of ash into the flow because of the decrease in settling velocity and the increase in fluid density. We note, however, that the addition of ash reduces the boundary Reynolds number (Re*) such that, at high ash concentrations and with fine-grained sediment, sediment tranport declines as the flow becomes hydraulically smooth. We determined that the Meyer-Peter- Muller bedload transport equation can be used to estimate transport rates in ash-laden slurries when Re* is greater than 35. Finally, we propose that ash slurries may evolve into progressively bulked debris flows through a positive feedback process between transport capacity and erosivity.
DE: 1225 Global change from geodesy (1222, 1622, 1630, 1641, 1645, 4556)
DE: 1810 Debris flow and landslides
DE: 1815 Erosion
DE: 1824 Geomorphology: general (1625)
SC: Hydrology [H]
MN: 2007 Fall Meeting