HR: 0800h
AN: H51E-0418    [Abstracts]
TI: Sediment Production Rates from Forest Thinning, Wildfires, and Roads: What is Important?
AU: * Brown, E
EM: ethanbr@lamar.colostate.edu
AF: Department of Forest, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523-1472 United States
AU: MacDonald, L H
EM: leemac@cnr.colostate.edu
AF: Department of Forest, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523-1472 United States
AU: Libohova, Z
EM: Zamir.Libohova@al.usda.gov
AF: Natural Resources Conservation Service, Tuscaloosa, Alabama, 12345 United States
AU: Rough, D
EM: drough@cnr.colostate.edu
AF: Department of Forest, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523-1472 United States
AU: Schaffrath, K
EM: keelin@cnr.colostae.edu
AF: Department of Forest, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523-1472 United States
AB: High-severity wildfires increase hillslope-scale erosion rates by at least several orders of magnitude, and the increased sediment yields pose a severe threat to downstream aquatic resources. Mechanical thinning is being used to reduce the threat of catastrophic wildfires, but there is little information on how thinning affects erosion rates. Repeated thinning operations generally necessitate an extensive road network, and unpaved roads are the dominant sediment source in many forested areas. In summer 2001 we began monitoring the effects of forest thinning on sediment production rates in the Colorado Front Range using a paired swale design. Over the past three years 20 swales have been mechanically thinned. Only very small amounts of sediment have been produced by either the control or the thinned swales, despite 30-minute rainfall intensities of 60-65 mm hr-1 on sites with slopes of 40-50%. In contrast, 10 pairs of swales burned at high severity in the 2002 Hayman wildfire, and the mean sediment production rate in the first three years after burning was 12 Mg ha-1 yr-1. By 2005 the mean sediment production rate from these burned swales had declined to only 0.07 Mg ha-1 yr-1. The measured sediment production rate from 14-26 unpaved road segments has ranged from 5 to 40 Mg per hectare of road surface per year, depending on the magnitude and intensity of summer thunderstorms. Detailed road surveys indicate that approximately 5% of the roads in our study area are connected to the stream channel network. If one assumes a road density of 1 km km-1 and a 5% delivery rate, unpaved roads are a chronic sediment source delivering approximately 0.005 Mg of sediment per hectare of catchment area per year. These results suggest that on a catchment scale, the long-term sediment yields from unpaved roads can approach the long-term sediment yields due to periodic, high-severity wildfires. Perhaps more importantly, certain aquatic resources may have very different sensitivities to pulsed versus chronic sediment inputs.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1804 Catchment
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
SC: Hydrology [H]
MN: Fall Meeting 2005