HR: 14:55h
AN: H32F-05    [PDF]
TI: Morphological Effects of Channel Confinement and Riparian Vegetation on Urban and Non-urban Streams of the Pacific Northwest
AU: * Segura Sossa, C
EM: catalina.segurasossa@colorado.edu
AF: University of Colorado, Geography Department, 260 UCB, Boulder, CO 80309-0260 United States
AU: Booth, D B
EM: dbooth@u.washington.edu
AF: Center for Water and watershed Studies, Department of Civil & Environmental Engineering, University of Washington, University of Washington, Box 352700, Seattle, WA 98195 United States
AB: The morphological influences of the near-riparian zone on channel morphology and channel responsiveness to urbanization were analyzed in low- and high-urbanized watersheds. Study sites included 22 reaches in a low-urbanized system on the Kitsap Peninsula in western Washington State, paired with 22 reaches having comparable slopes and drainage areas from highly urbanized watersheds in and east of the City of Seattle. Remarkably different channel morphologies were observed between low and high-urbanized reaches. Low-urbanized reaches displayed mainly forced pool-riffle morphology; the high-urbanized reaches were dominated by constrained (armored) step-pool and plane-bed morphologies. In comparison, the low-urbanized reaches had less bank erosion and more in-stream wood, pools, and sediment storage. In low-urbanized watersheds, channel morphology (as quantified by measures of in-stream wood frequency and distribution, pool frequency, sediment storage, and bank erosion) was related to the degree of channel confinement and to characteristics of the near-riparian vegetation. High-urbanized reaches, in contrast, were substantially less sensitive to the condition of the near-riparian zone due to the common stream disconnection with the floodplain triggered by the placement of bank-armoring structures. From a management perspective, an increase in woody debris in plane-bed reaches could yield an eventual morphologic shift to forced pool-riffle. However, increased wood loading in these channels does not guarantee such a shift. These channels also need to be reconnected to their forested floodplain and to the channel-bank sediment, which provide long-term sources of both large woody debris and gravel. In the case of anthropogenically confined channels, restoration is even more challenging because sustainable morphologic improvements would require removal of bank-armoring structures to facilitate that reconnection. The common practice of adding logs results in short-term improvements, but is not likely to provide a sustainable solution in many settings unless equal consideration is given to geomorphic processes that maintain floodplain connectivity.
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting