ERDC/CHL CHETN-VII-4
June 2002
Figure 7. Longitudinal profile through north-south swath
METHODOLOGY: When it was determined that the swaths had captured sufficient bed wave
movement during their time spans, 2.3 to 4.8 hours, the ISDOT method was applied. The
coordinates of a rectangle common to all four swaths were identified. Then a computational grid
consisting of 0.3048-m- (1-ft-) squares was made. The data from each of the four swaths
("snapshots") were interpolated to four separate grids. These grids with their associated bathymetric
elevations represented the exact same surface at four different points in time. Any one grid can be
subtracted from another to produce a difference plot. The difference for any square foot between
surface 1 or 2, for example, represents the change in volume over time for that incremental area.
Presently, both deposition into and scour out from any element are considered as positive transport.
Adding up all the incremental changes in volume across the section produces the net change in
volume over time for the section. This value can then be multiplied by the density of the sediment-
water mixture to yield a bed-load transport rate.
The concept, although simple in principle, has not been used previously by any other researcher(s).
There are probably at least two very good reasons. First, all literature seems to focus on the
longitudinal profiles of the waves. Thus in quantifying these characteristics of the waves, different
methods of bed-load calculations are carried out to determine the bed-load transport rate of a given
wave. There are many excellent studies carried out in this manner as in Simons, Richardson, and
Nordin (1965), Willis and Kennedy (1977), and Mahmood (1985). Kennedy and Odgaard (1991)
present an excellent review of riverine sand dune literature. Other than empirical methods based on
sediment and hydraulic characteristics, they all appear to focus on two-dimensional (2-D) wave
shape and celerity, or some type of statistical analysis of 2-D dune profiles. A bed-load transport
rate calculated in either of these last two manners is applicable to only the 2-D wave under
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