HR: 15:00h
AN: H43A-05    [Abstracts]
TI: Sediment from Wildfires: Production, Delivery, and Recovery at Different Spatial Scales
AU: * MacDonald, L H
EM: leemac@cnr.colostate.edu
AF: Watershed Science Program, Colorado State University, Fort Collins, CO 80523-1472, United States
AU: Larsen, I J
EM: larseni@cnr.colostate.edu
AF: Watershed Science Program, Colorado State University, Fort Collins, CO 80523-1472, United States
AB: Sediment production from wildfires is of increasing concern in the western U.S. due to the severe effects on water quality and aquatic resources, and the increase in area burned due to increased forest densities and global warming. Over the past 6 years we have been measuring post-fire effects and sediment production from seven wildfires, three prescribed fires, and 40 unburned hillslopes in the Colorado Front Range. The resulting dataset includes a series of process-based studies, 600 plot-years of sediment production data at the hillslope scale, and changes in channel cross-sections at scales ranging from 0.01 ha to 6 km2. In unburned areas surface runoff and erosion is extremely rare. After a high-severity fire the threshold for overland flow drops to 7-10 mm hr- 1, and in the first two years after burning the median surface erosion rates are 5-10 Mg ha-1 yr-1. Hillslope runoff and sediment production rates drop to near-background levels within 3-5 years after burning, and recovery rates are primarily a function of vegetative regrowth. Approximately 80 percent of the post-fire sediment is derived from rill and channel incision in headwater areas, so nearly all of the eroded sediment is being delivered to the stream channel network. The downstream transport of this material adversely affects water quality and causes extensive aggradation. The relatively rapid recovery at the hillslope scale reduces surface runoff rates and sediment transport capacities in downstream channels. This means that the smaller streams cannot remove much of the accumulated sediment, and post-fire channel recovery may take hundreds of years as compared to the 3-5 years needed for hydrologic recovery at the hillslope scale.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1815 Erosion
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Joint Assembly