HR: 16:15h
AN: H42L-02    [PDF]
TI: A modeling study on the effects of vegetation and disturbances on episodic sediment delivery
AU: Tarboton, D G
EM: dtarb@cc.usu.edu
AF: Utah State University, 4110 Old Main Hill, Logan, UT 84322 United States
AU: * Istanbulluoglu, E
EM: erkan@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Pack, R T
EM: rtpack@cc.usu.edu
AF: Utah State University, 4110 Old Main Hill, Logan, UT 84322 United States
AU: Luce, C H
EM: cluce@fs.fed.us
AF: US Forest Service Rocky Mountain Research Station, Myrtle Str., Boise, ID 83702 United States
AB: In steep forested basins of the Western U.S. episodic catastrophic erosion events are often linked to extreme climate events together with vegetation disturbances by wildfires and anthropogenic activities such as timber harvest. These disturbances have been shown to dramatically accelerate erosion rates over rates in undisturbed forests at short time-scales. Over longer time scales, however, characterization of the frequency and magnitude of extreme events has been hampered by the lack of data and techniques to date past low frequency and large magnitude events. Here we investigate the controls of forest vegetation, natural (wildfires) and anthropogenic (harvest) disturbances on the frequency and magnitude of sediment delivery from a small watershed (~ 3.9 km2) in the Idaho Batholith through numerical modeling. Our model simulates soil production, gully erosion, forest vegetation dynamics, shallow landsliding and debris flow generation over millennial time scales. In the model, vegetation provides root cohesion and surface resistance to channel initiation. Fire and harvest reduce the vegetation and fire leads to water repellent soils. Our simulation results compare well with published data for sediment yields of recently observed catastrophic events, and long term averages over ~10,000 years in the Idaho Batholith. By experimenting with different vegetation scenarios we found that the magnitude of episodic stream sediment inputs mostly depends upon the frequency of disturbance. Large but infrequent episodic sediment inputs occur when when vegetation was not disturbed by wildfires or harvesting over thousands of years. When forest disturbance is modeled through the simulation of either wildfires or harvesting, episodic sediment inputs are more frequent and occur during accelerated erosion periods following disturbances. Because for this watershed the long-term rate-limiting factor in sediment delivery is modeled to be soil production, the magnitude of episodic sediment delivery is smaller under the presence of disturbances.
UR: http://www.engineering.usu.edu/cee/faculty/dtarb/
DE: 1719 Hydrology
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting