BULK RELATIONS FOR TRANSPORT OF TOTAL BED MATERIAL LOAD

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CHAPTER 12 BULK RELATIONS FOR TRANSPORT OF TOTAL
BED MATERIAL LOAD
Sediment-laden meltwater emanating from a glacier
in Iceland. The flow is from top to bottom. The
flow to the left is braided, whereas that to the
right is meandering. Image courtesy F. Engelund
and J. Fredsoe.
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QUANTIFICATION OF TOTAL BED MATERIAL LOAD
The total bed material load is equal to the sum
of the bedload and the bed material part of the
suspended load in terms of volume transport per
unit width, qt qb qs. Here wash load, i.e.
that part of the suspended load that is too fine
to be contained in measurable quantities in the
river bed, is excluded from qs. Total bed
material load is quantified in various ways in
addition to qt Flux-based volume concentration
Ct qt/(qt qw) Flux-based mass concentration
Xt ?sqt/(?sqt ?qw) Flux-based mass
concentration in parts per million
Xt?106 Concentration in milligrams per liter
?sqt/(qt qw)?106, where qt and qw are in m2/s
and ?s is in tons/m3. In the great majority of
cases of interest qt/qw ltlt 1, so that the
concentration in milligrams per liter is
accurately approximated by the mass concentration
in parts per million.
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RELATION OF ENGELUND AND HANSEN (1967)
A variety of relations are available for the
prediction of bulk total bed material load. Most
of them are based on the regression of large
amounts of data. Five such relations are
reported here. Although the data bases for some
of them include gravel, they are not designed for
gravel-bed streams. As such, their use should be
restricted to sand-bed streams. Perhaps the
simplest of these relations is that due to
Engelund and Hansen (1967). It takes the form
where
The relation is designed to be used in
conjunction with the formulation of hydraulic
resistance of Engelund and Hansen (1967)
presented in Chapter 9. Brownlie (1981) has
found the relation to perform very well for field
sand-bed streams.
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RELATION OF BROWNLIE (1981)
The formulation of Brownlie (1981) can be
expressed as
In the above relations ?g is the geometric
standard deviation of the bed sediment and cF
takes the value of 1 for laboratory conditions
and 1.268 for field conditions. The relation is
designed to be used in conjunction with the
Brownlie (1981) formulation for hydraulic
resistance.
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RELATION OF YANG (1973)
The formulation of Yang (1973 see also 1996) can
be expressed as
In the above relations vs is the fall velocity
associated with sediment size D50.
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RELATION OF ACKERS AND WHITE (1973)
The formulation of Ackers and White (1973) can be
expressed as
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RELATIONS OF KARIM AND KENNEDY (1981) AND KARIM
(1998)
The formulation of Karim and Kennedy (1981) can
be expressed as where uc can be evaluated
from Brownlies (1981) fit to the original
Shields curve The above relation may be used
in conjunction with their relation for hydraulic
resistance presented in Chapter 9. Karim (1998)
also presents a total bed material load equation
that is fractionated for mixtures
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REFERENCES FOR CHAPTER 12
Ackers, P. and White, W. R., 1973, Sediment
transport new approach and analysis, Journal of
Hydraulic Engineering, 99(11), 2041-2060. Brownlie
, W. R., 1981, Prediction of flow depth and
sediment discharge in open channels, Report No.
KH-R-43A, W. M. Keck Laboratory of Hydraulics and
Water Resources, California Institute of
Technology, Pasadena, California, USA, 232
p. Engelund, F. and E. Hansen, 1967, A Monograph
on Sediment Transport in Alluvial Streams,
Technisk Vorlag, Copenhagen, Denmark. Karim, F.,
1998, Bed material discharge prediction for
nonuniform bed sediments, Journal of Hydraulic
Engineering, 124(6) 597-604. Karim, F., and J.
F. Kennedy, 1981, Computer-based predictors for
sediment discharge and friction factor of
alluvial streams, Report No. 242, Iowa Institute
of Hydraulic Research, University of Iowa, Iowa
City, Iowa. Yang, C. T., 1973, Incipient motion
and sediment transport, Journal of Hydraulic
Engineering, 99(10), 1679-1704. Yang, C. T.,
1996, Sediment Transport Theory and Practice,
McGraw-Hill, USA, 396 p.