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Title: Examining the physical meaning of the bank erosion coefficient used in meander migration modeling

Author
item CONSTANTINE, CANDICE - UNIV OF CALIFORNIA
item DUNNE, THOMAS - UNIV OF CALIFORNIA
item Hanson, Gregory

Submitted to: Geomorphology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2008
Publication Date: 5/15/2009
Citation: Constantine, C.R., Dunne, T., Hanson, G.J. 2009. Examining the physical meaning of the bank erosion coefficient used in meander migration modeling. Geomorphology. 106(3-4):242-252.

Interpretive Summary: In floodplain management a widely used method for predicting river meander evolution relies on a coefficient of bank erosion. This coefficient is commonly determined based on historical measurements of river meander migration. This study attempts to relate historical measurements of this coefficient to measurable physical characteristics of the river channel bank of the Sacramento River, CA, USA. The coefficient of bank erosion calculated from meander rates and near bank velocities was related to erosion resistance measurements of the bank material. The material erosion resistance measurements were obtained using an in-situ jet-test device. The material resistance measurements statistically explain much of the observed variability of the coefficient of bank erosion. This finding opens up the possibility that coefficient of bank erosion may be estimated directly from field data, enabling prediction of meander migration rates for systems where historical data are unavailable or controlling conditions have changed. Another implication is that vegetation plays a limited role in affecting long-term meander migration rates of large rivers like the Sacramento River. These hypotheses require further testing with data sets from other large rivers.

Technical Abstract: Widely used models of meander evolution relate migration rate to vertically averaged near-bank velocity through the use of a coefficient of bank erosion (E). In applications to floodplain management problems, E is typically determined through calibration to historical planform changes, and thus its physical meaning remains unclear. This study attempts to clarify the extent to which E depends on measurable physical characteristics of the channel boundary materials using data from the Sacramento River, California, USA. Bend-average values of E were calculated from measured long-term migration rates and computed nearbank velocities. In the field, unvegetated bank material resistance to fluvial shear (k) was measured for four cohesive and noncohesive bank types using a jet-test device. At a small set of bends for which both E and k were obtained, we discovered that variability in k is linearly related to the variability in E. The form of this relationship suggests that when modeling long-term meander migration of large rivers, E depends largely on bank material properties. This finding opens up the possibility that E may be estimated directly from field data, enabling prediction of meander migration rates for systems where historical data are unavailable or controlling conditions have changed. Another implication is that vegetation plays a limited role in affecting long-term meander migration rates of large rivers like the Sacramento River. These hypotheses require further testing with data sets from other large rivers.