HR: 08:00h
AN: H41G-01    [Abstracts]
TI: Channel Geometry of Mountain Rivers Within the Debris-Flow Process Domain of the Idaho Batholith
AU: * Buffington, J M
EM: jbuffington@fs.fed.us
AF: USDA Forest Service, Rocky Mountain Research Station, 316 E. Myrtle St., Boise, ID 83702 United States
AU: Scheidt, N E
EM: scheidtn@uidaho.edu
AF: University of Idaho, Ecohydraulics Research Group, Dept. of Civil Engineering, 800 Park Blvd. Suite 200, Boise, ID 83712 United States
AU: Welcker, C W
EM: welcker@uidaho.edu
AF: University of Idaho, Ecohydraulics Research Group, Dept. of Civil Engineering, 800 Park Blvd. Suite 200, Boise, ID 83712 United States
AB: Channel width {\it w} and depth {\it d} exhibit systematic downstream changes with increasing drainage area {\it A} and hydraulic discharge ({\it w = cA$^{b}$, d = eA$^{f}$}). These relationships vary regionally as a function of physiography (climate, topography, and geology), but exhibit grossly similar trends across many orders of magnitude in drainage area, and across different channel types (e.g., alluvial, bedrock and, in some instances, tidal channels). The consistency of these relationships likely reflects the fact that each of these channel types is formed by hydraulic forces of flowing water. However, headwater rivers in mountain basins experience a combination of fluvial discharge and periodic passage of debris flows and hyperconcentrated flows. Consequently, channel geometry of headwater rivers may reflect a competition between fluvial and mass-wasting processes. We conducted field surveys of channel characteristics in headwater basins of the Idaho Batholith to examine this issue and to determine if channel geometry can be used to infer either the recency or dominance of these competing geomorphic processes (fluvial vs. mass wasting). Mass-wasting events are common occurrences in the study area, resulting from summer thunderstorms and winter rain-on-snow events. Moreover, the magnitude and frequency of mass wasting increases in the study area following wildfires that alter vegetation, soil permeability and consequent basin hydrology. Results indicate that headwater channels recently impacted by debris flows tend to be wider, but have width-drainage area exponents similar to lowland alluvial channels ({\it b} = 0.5).
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting