River Meandering

487 Pages·15.377 MB·English

Water Resources Monograph 12
River
Meandering
SyunsukeIkeda
Gary Parker
Editors
American Geophysical Union
Publishedunderthe aegis ofthe AGUWaterResourcesMonographBoard.
Libraryof Congress Cataloging-in-Publication Data
RivermeanderingSyunsukeIkedaand GaryParker, editors.
p. cm. - (Waterresources monograph: 12)
ISBN0-87590-316-9
1. Meanderingrivers. I. Ikeda, Syunsuke. II.Parker, Gary. III. Series.
GB1205.R55 1989
551.48'3-dc20 89-6873
Copyright 1989 by the American Geophysical Union, 2000 Florida Avenue,
NW, Washington,,DC 20009
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CONTENTS
1. Boundary Shear Stress and Sediment Transport in River Meanders of
Sand and Gravel, by Willianl E. Dietrich and Peter Whiting 1
2. Sedimentary Controls on Channel Migration and Origin of Points Bars in
Sand-Bedded Meandering Rivers, by Hiroshi Ikeda 51
3. Flow in Meandering Channels with Natural Topography, by Jonathan 1v1.
Nelson and J. Dungan Smith 69
4. Sedinlent Transport and Sorting at Bends, by Syunsuke Ikeda 103
5. Sediment Control by Submerged Vanes. Design Basis, by A. Jacob
Odgaard and Anita Spoljaric 127
Q..,
6. Analysis ofN-D Bed Topography Model for Rivers, by Nico Struiks111a
and AI~ssandra Crosato 153
7. Linear Theory of River 1\1eanders, by I-Ielgi Johannesson and Gary
Parker 181
8. Studies on Qualitative and Quantitative Prediction of Meander Channel
Shift, by I(azuyoshi Hasegawa 215
9. Finite Amplitude Development of Alternate Bars, by Shoji Fukuoka 237
10. Alternate Bars and 1\1eandering; Free, Forced and 1\.fixed Interactions,
by G. Seminara and 1\1. Tubino 261
11. Evolution and Stability of Erodible Channel Beds, by Jonathan 1\/1.
Nelson and J. Dungan Slnith 321
12. Observations on Several Recent Theories of Resonance and Overdeepening
in 1\1eandering Channels, by Gary Parker and Helgi Johannesson 379
13. Bar and Channel Forluation in Braided Streanls, by Yuichiro Fujita 417
14. Topographic Response of a Bar in the Green River, Utah to Variation in
Discharge, by E.D. Andrews and J. 1\1. Nelson 463
iii
PREFACE
River channel pattern comes in three flavors: straight, meandering, and
braided. Of these, meandering is perhaps the most common, but at the same
time the most mysterious: it is strikingly rich in pattern, yet is encumbered
with neither the sterile order of its straight cousin, nor the undecipherable
disorder of its braided relative.
Consider Figures 1 and 2 herein. The former is of the artificially
straightened Naka River, Shikoku, Japan. Thwarted in its quest for a
meandering planform, the river has, nevertheless, generated of its own the
precursor known as alternate bars. In the latter photograph, a pair of images
of the East Nishnabotna River, Iowa, USA, illustrate the elegance of the
sinuous river, and the inexorable migration and deformation of bends so
characteristic of freely meandering strealns.
The inception and growth of meander bends, and their eventual demise
through the mechanism of cut-off formation, have been treated by many, and
the literature on the subject lies scattered about the world in such fields as
hydraulics, geology, and geography. This volume represents an attempt to
dra\v together an international group of theoretical researchers at the cutting
edge, supplemented with several leading field-oriented researchers. (Indeed,
some among our numbers comfortably occupy both camps.) The underlying
philosophy \vas an attempt to extract from the various schools a more unified
understanding of the mechanics of meandering, as a base from which to build
for the future.
The concept \vas originally born in 1981, in a letter communicated fron1
S. Ikeda to G. Parker. It developed rapidly in the aftermath of the Specialty
Conference on River Meandering, held in Ne\v Orleans in 1983 under the
sponsorship of the American Society of Civil Engineers. Eventually, our
proposal, "Development and Application of the Theory of River Meandering",
was adopted in 1985 by the U.S. National Science Foundation and the Japan
Society for the Promotion of Science, as a bilateral research project.
This monograph is not simply a collection of papers from a conference,
but rather the product of a joint research effort of unique and unusual
character. In order to appreciate the mood of the volunle, it is of use to
describe hovv the project proceeded.
The core group of participants \\Tas chosen to consist of five Japanese
and five Americans, all relatively young. (These \vords will surely come back
to haunt us.) The research was organized about three workshops. The first
of these, held in Tokyo in July of 1985, was en1bedded in the midst of a
t,vo-week tour of rivers and research facilities, one that ,vas to take us to
three of the four lnajor islands of Japan. Naturally, the Naka River, sho,vn in
Figure 1, was on the itinerary. The second \vorkshop was held in September
of 1986, at the Brinkerhoff House, a lodge on Jenny Lake, Grand Teton
v
vi PREFACE
Figure 1. Alternate bars in the Naka River, Tokushima Prefecture, Japan
(courtesy Tokushima Construction Office, Ministry of
Construction, Japan).
National Park, Wyoming (Figure 3). It was part of a similar two-week series
of site visits which eventually included nine rivers in California, Wyoming,
Iowa (Le. the East Nishnabotna River), and Minnesota. The third and final
workshop was held at Poipu Beach, Kauai, Hawaii, in October of 1987 (Figure
4).
The researchers were in contact not only during the workshops, but
through the length of the site visits. We travelled together, ate together, and
often jointly occupied hotel rooms. During our stay at Jenny Lake, we even
washed dishes and swept the floor together, and in a cooperative effort of
special import, chased a bear off the veranda. The workshops were all of
relatively free format, with the emphasis on active, and often heated
discussion. The' extended period together helped greatly to reduce the
language barrier, and facilitated a seemingly unending interplay of ideas. A
Ikeda and Parker vii
Figure 2. The meandering East Nishnabotna River just south of Red Oak,
Iowa: (left) October 5, 1973; (right) May 25, 1979. Channel
migration can be clearly discerned (courtesy A. J. Odgaard).
spin-off of this atmosphere is an exchange of researchers that continues until
this day.
In order to provide a more complete perspective on the problem, two
leading European researchers were invited to participate in the final workshop.
The monograph thus includes fourteen papers authored by: the Japanese,
viii PREFACE
Figure 3. Thesecond workshop, held at Brinkerhoff House, Jenny Lake,
Wyoming, on September 8, 1986.
American, and European participants and their graduate students. It is fair to
say that no individual came out of the workshops without a significantly
changed perspective on the problem of river meandering.
The participants thus included eight civil engineers, three geologists, and
a geographer. The tone of the monograph is mechanistic and interdisciplinary.
The interplay between theory, computation, experiment, and field observation
Figure 4. The third workshop, held at the Poipu Beach Sheraton Hotel,
Kauai, Hawaii, on October 21, 1987.
Ikeda and Parker ix
is fully exploited. One sign evidencing the heightened spirit of cooperation
and understanding is the prodigious cross-referencing among the papers.
The list of people and organizations deserving thanks for making this
effort possible is long. First and foremost are the U.S. National Science
Foundation and the Japan Society for the Promotion of Research, who
provided the funding. In Japan, the Ministry of Construction and the
I-Iokkaido Development Bureau deserve special thanks. In the United States,
the Department of the Interior and the Army Corps of Engineers greatly
facilitated the program. Various graduate students from the University of
California, Berkeley and the University of Minnesota drove vehicles for us.
Professor J. F. I(ennedy kindly made a personal trip to the East Nishnabotna
River to show us the "Iowa Vanes" being tested there as a means of
preventing bank erosion. Patricia Swanson, Diana Dalbotten, and Donna
Elftmann spent long hours typing and editing the papers to a common format,
enabling us to meet the many externally-imposed deadlines.
It is our hope that the volume represents a \vatershed in progress on
river meandering, and a stimulus to younger researchers who might be inclined
to en1bark upon the study of this most elegant and beautiful of natural
phenomena.
Syunsuke Ikeda
Gary Parker
Water Resources Monograph River Meandering Vol. 12
Copyright 1989 by the American Geophysical Union.
Boundary Shear Stress and Sediment Transport
In River Meanders of Sand and Gravel
William E. Dietrich and Peter Whiting
Department of Geology and Geophysics
University ofCalifornia, Berkeley, 9-17!O
Field measurements in a sand-bedded river and in two gravel-bedded ones
are compared to examine controls on boundary shear stress fields, sediment
transport processes, and sorting in meanders. Analysis of detailed flow field
measurements in the sand-bedded river meander and over a gravel-bedded
alternate bar reveals a well-defined spatial structure to the magnitude and sign
of forces controlling boundary shear stress that arise from topographically
induced spatial accelerations. The relationship between bedload transport and
boundary shear stress fields in river meanders varies with size and
heterogeneity of bed material. In bends of moderately to well sorted sand in
flows generating boundary shear stresses well above critical (such as in large
sandy rivers), downstream varying boundary shear stress is matched by
topographically-induced cross-stream transport of sediment. In meanders with
high excess shear stress but poorly sorted coarse sand and fine gravel,
boundary shear stress variation downstream is partially matched by surface
grain size adjustments and by net cross-stream sediment flux. Maxima of
bedload transport rate and boundary shear stress do not correspond in some
areas. In gravel-bedded meanders with low excess boundary shear stress and
low sediment supply, bedload may be much finer than the bed surface, and
significant areas of bar surface are covered with grain sizes that constitute a
very small portion of the bedload. Substantial bedload transport may only
occur over a narrow portion of the bed width where boundary shear stress
relative to critical stress of the surface is highest and where the sediment flux
from upstream is locally concentrated. In· this case, grain size adjustments
dominate over topographically-induced cross-stream sediment transport in
controlling the relationship between boundary shear stress and bedload
transport fields.
Introduction
Morphologic adjustments occur in rivers when the divergence of the
boundary shear stress field causes sediment flux divergence leading to either
net scour or deposition. In .exploring the mechanisms of morphologic
adjustments in rivers, then, two key questions can be posed: 1) what is the
relationship between the boundary shear stress field and channel topography,
and 2) what is the relationship between the boundary shear stress field and
the sediment transport field. Theories for channel morphology must partially
assume the answer to these questions in order to solve the complex coupled
Copyright American Geophysical Union
Water Resources Monograph River Meandering Vol. 12
2 BoundaryShearStress
flow and sediment transport equations. A goal of empirical field studies
should be to test these assumptions. Both of these questions are addressed
here.
The first question is motivated in part by debate over the role of
topographically-induced convective accelerations in the overall downstream and
cross-stream force balance controlling flow through river meanders. Scaling
arguments by Smith and McLean [1984] and Nelson [1988] showed that such
convective accelerations were large and properly belonged in a "zero-order"
force balance when the equations of motion are solved by perturbation
expansion. Although Dietrich and Smith [1983] reported some data on
convective accelerations. from a field study, it was recently concluded by
Odgaard and Bergs [1988, p. 43] that in particular "they were not able to
provide clear cut evidence from their field data..." for the inclusion of
convective acceleration terms neglected in the seminal theory by Engelund
[1974]. The first part of our paper endeavors to show "clear cut" evidence
that convective accelerations associated with downstream changing topography
are large and systematic in their contribution to the total force balance in a
natural meandering river with well developed point bars. These accelerations
are computed from the spatial derivatives of large terms; consequently, they
are prone to large error even in laboratory settings, but we argue here that the
observed general spatial pattern of these terms in a bend and the consistent
magnitude of these terms are well defined with our field data. We also report
data on forces due to convective accelerations obtained from detailed
measurements over a bar in a nearly straight reach to demonstrate the
significance of these terms in the alternate bar case. Although the issue
regarding convective accelerations may seem rather narrow, it has broad
implications.
The key effect of downstream changes in bed topography on flow is not so
much on the magnitude of the boundary shear stress at any point on the
stream bed, but rather on the direction of the boundary shear stress vector,
particularly over the top of the point bar. In a sequence of bends, the effects
of changing curvature alone on the growth and decline of superelevation will
cause a zone of maximum boundary shear stress to shift from near the
upstream inside bank to the downstream outside bank [see, for example,
Dietrich, 1987, p. 181]. Dietrich [1987] has shown that, even using a
downstream force balance just between the pressure gradient and boundary
shear stress (Le. no downstream convective accelerations included), the
vertically-averaged downstream velocity field is fairly closely predicted at his
Muddy Creek study site. Not surprisingly then, others, Le. Odgaard [1988]
and Bridge [19831, have also modeled relatively accurately aspects of Muddy
Creek flow and geometry with equations which did not include all
similarly-scaled convective accelerations. But neglecting to include all
appropriate topographically-induced convective accelerations prevents fully
quantifying the most important effect of the point bar: point bars force the
flow over the bar toward the opposite bank, even at the bed. This effect,
called quite graphically "topographic steering" by Nelson [1988], is linked to
the convective acceleration terms, as illustrated in Figure 1. In essence,
shoaling of the flow over the point bar generates convective accelerations that
cause a pressure rise over the bar and drop over the pool such that, in the
cross-stream direction, centrifugal force exceeds the opposing pressure gradient
force and net outward flow occurs. Put more" simply, the flow goes around
the bar.
This "shoaling" or "steering" effect is particularly important because it
provides a mechanism for topographic adjustments due to stage change and for
the development of an equilibrium bar topography, especially in channels with
relatively flat bar tops. The instability that leads to point bar growth in
Copyright American Geophysical Union