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Spatial autoregressive structure in meander evolution; with Suppl. Data 91-31

David Jon Furbish
Spatial autoregressive structure in meander evolution; with Suppl. Data 91-31
Geological Society of America Bulletin (December 1991) 103 (12): 1576-1589

Abstract

The migration of a river bend depends in part on the high flow velocities that characteristically impinge on its outside bank. Recent models have treated this in terms of a spatial convolution, whereby local bend migration is mathematically a weighted aggregate of up-stream curvature and bed topography. The convolution model can be tested using river migration data after it is discretized and recast into a finite autoregressive form. Published isochrones marking former positions of bends on the Beatton River, Canada, support the hypothesis that rates of bend migration follow a convolutional relation. In addition, a comparison of the underlying flow model with published flume experiments involving constant-curvature bends illustrates how it predicts the near-bank depth-averaged velocity associated with a forced-bar topography in absence of free bars. The autoregressive form of the model is equivalent to a stochastic linear-difference equation; this allows bend curvature to be treated as a random process. Cast in the frequency domain, the convolution model predicts that big bends tend to grow at the expense of little bends and curvature irregularities in complex trains; there exists no tendency for preferential growth of an intermediate bend size. The model also predicts the well-known shift of maximum migration rates to positions down-stream of curvature apexes and implies that the magnitude of this shift increases with decreasing bend size. Predicted shifts compare well with published, measured shifts on the Nishnabotna River, Iowa. The sensitivity of the meandering process to initial bend geometries and entrance flow conditions ensures that diverse bend shapes arise along freely migrating rivers independently of factors such as unsteady flow and nonuniform erodibility. No single geometrical form serves as an asymptotic, evolutionary state for individual bends.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 103
Serial Issue: 12
Title: Spatial autoregressive structure in meander evolution; with Suppl. Data 91-31
Author(s): Furbish, David Jon
Affiliation: Fla. State Univ., Dep. Geol., Tallahassee, FL, United States
Pages: 1576-1589
Published: 199112
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 66
Accession Number: 1991-047190
Categories: Geomorphology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch maps
N51°00'00" - N72°00'00", W130°00'00" - E173°00'00"
N48°25'00" - N60°00'00", W139°00'00" - W114°00'00"
N37°00'00" - N41°00'00", W109°00'00" - W102°00'00"
N24°30'00" - N31°00'00", W87°30'00" - W80°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1991
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