HR: 1330h
AN: H42E-1121    [PDF]
TI: Assessing the Role of Floods, Land Conversion and Bank Materials in Determining Channel Change Along the Willamette River, 1850-1996
AU: * Wallick, J R
EM: wallickr@geo.orst.edu
AF: Department of Geosciences Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331 United States
AU: * Wallick, J R
EM: wallickr@geo.orst.edu
AF: Department of Bioengineering Oregon State University, 116 Gilmore Hall, Corvallis, OR 97331 United States
AU: Denlinger, R
EM: roger@usgs.gov
AF: Cascade Volcano Observatory, 1300 SE Cardinal Court, Vancouver, WA 98683 United States
AU: Lancaster, S
EM: Stephen.Lancaster@geo.orst.edu
AF: Department of Geosciences Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331 United States
AU: Bolte, J
EM: boltej@engr.orst.edu
AF: Department of Bioengineering Oregon State University, 116 Gilmore Hall, Corvallis, OR 97331 United States
AB: Floods and land development often trigger dramatic changes in planform and alter the evolution of floodplains. In this study, we combine historical analysis with a 2D flood model and a meander migration model along a 200 km section of the Willamette River in western Oregon to examine the relative importance of floods, bankful flows and land use patterns in determining channel change. Digitized historical datasets from 1850, 1895, 1932, 1972 and 1995 are used to calculate rates of channel change and to measure trends in channel width and sinuosity. Historical maps also provide information on riparian vegetation, bank materials and revetments. To estimate erosion resulting from the 1996 flood, we use power estimates derived from the 2D flood model of Denlinger et al., (2002). Using this model, the distribution of observed high water marks allows us to estimate average bed roughness during the flood. The product of velocity and bed shear stress estimated from bed roughness gives us a pattern of stream power that we can compare with observed channel changes. We compare these results with near-bank velocities (a proxy for bank shear stress) generated by bankful flows using a linear meander migration model in which velocity is the result of channel curvature. By comparing estimated shear-stress distributions from both models with observed erosion patterns, we can observe differences in the magnitude and style of erosion arising from each mechanism. Preliminary results show that avulsions, channel widening and decreases in sinuosity are associated with historic flooding. Periods of lower magnitude flows allow lateral migration to become dominant, thereby increasing sinuosity and migration rate. Floodplain variables such as bank materials, riparian vegetation and revetment placement will be analyzed to determine their influence on migration rates under different flow regimes. Further analysis will allow us to compile information on planform, erosion rate, bank materials and landuse conditions over the 5 time periods. By linking this information to model results, we hope to identify combinations of floodplain variables and flow conditions that support unique styles or rates of channel change.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting