HR: 16:00h
AN: H44B-01 INVITED    [Abstracts]
TI: Dynamic Adjustments in Channel Width in Response to a Forced Diversion: Gower Gulch, Death Valley National Park, California
AU: * Snyder, N P
EM: noah.snyder@bc.edu
AF: Boston College, Dept. of Geology and Geophysics 140 Commonwealth Avenue, Chestnut Hill, MA 02467, United States
AU: Kammer, L L
EM: schultli@gmail.com
AF: Boston College, Dept. of Geology and Geophysics 140 Commonwealth Avenue, Chestnut Hill, MA 02467, United States
AB: We study the 1941 diversion of Furnace Creek Wash (drainage area 439 km²) into Gower Gulch (5.8 km²) as an experiment in the transient response of channel geometry to a large change in water and sediment discharge. We measure sequential changes in valley width using a time series of aerial photographs (1948-1995), airborne laser elevation data from 2005, and a field survey. We find that response of the system varies depending on the pre-diversion channel morphology and geology. In two steep knickzone segments, narrowing, knickpoint retreat, and bedrock incision dominates-- a detachment-limited response. In the relatively low-gradient main part of Gower Gulch, fine-grained, soft sedimentary rocks underlie the channel, and widening dominates as the large, coarse post-diversion sediment load covers the channel bed. The response in this section is transport limited, with only modest incision and adjustments in gradient. Two different processes appear to cause the channel to widen. (1) In many reaches, the stream is attacking the valley walls, as evidenced by fresh plucking and scour marks. This probably occurs because the bed in the middle of the channel is alluviated and protected, which minimizes the opportunity for vertical incision. (2) Some reaches have experienced aggradation, which widens the valley by filling it in. This occurs in places where storage space exists (splay deposits in small tributary mouths, fill terraces in the wide valleys at larger tributary mouths) or in reaches upstream of constrictions. Over long periods, the lowering rate of Gower Gulch probably depends on knickpoint retreat, but the present-day response of this non-steady-state system is a hybrid of incision and narrowing in detachment-limited reaches and widening in transport-limited reaches. This system demonstrates the importance of initial conditions and evolving channel geometry in setting the transient response of rivers.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1815 Erosion
DE: 1825 Geomorphology: fluvial (1625)
DE: 1855 Remote sensing (1640)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting