ERDC/CHL CHETN-VII-4
June 2002
the material of which the bed is composed that is transported by rolling and sliding,... and by
skipping, hopping, or jumping. These three words seem to be interchangeably used in a loose sense
by many authors, and might even be what authors refer to when they speak of saltating particles.
However, the important distinctions should be noted. Einstein defines jumping as leaps of no more
than 100 grain diameters long. Bagnold calls bed load the movement of particles whose successive
contacts with the bed are limited by the effects of gravity. That means that the particles do not go
into suspension. The suspended bed-load material is then defined as that in which the excess weight
of the particles is supported by the upward impulses of turbulence. Van Rijn chooses a similar
definition. For this study a definition similar to that of Bagnold and van Rijn was preferred.
Bedload for the purposes of the ISDOT method, is defined as sediment that is transported in a stream
by rolling, sliding, or saltating along the bed and very close to it. For the calculations of bed load
moving in dunes or sand waves, the following condition should be added. If particles temporarily go
into suspension for distances greater than the length of the smallest of the dune lengths, then these
particles should be considered as suspended. Otherwise they can be considered as bed load. The
reason for this distinction will be presented in later papers.
CONSTRAINTS: The movement of a sand wave occurs when the upstream surface to the crest is
scoured and then this material is subsequently deposited on the downstream face of the wave. With
this mechanism of movement in mind, several limitations exist in order for this computational
procedure to provide meaningful results. First, as noted in the definitions, the particles that move the
sand wave cannot completely jump over an entire wave. Second, the speed of the wave must be
such that the length that it travels in a given time must not be greater than the length of the
computational grid. Third, it is assumed that within a given control volume the bed-load transport
rate is in a steady state. Finally, with regards to sand wave regime theory, the flow cannot be such
that the dune bed will transition into plane bed or antidunes.
Additional constraints are related to the collected data. For either the ISDOT or wave celerity
method to provide valid results, the sequential "snapshots" of the bathymetric features must be
accurate in space and time and measured to the same datum. All of these constraints have been
considered in the development of the ISDOT method.
SITE: The location of the monitoring site and specific study area used to develop this measurement
technique is Pool 8 on the Upper Mississippi River, just south of LaCrosse, WI. Several
photographs and descriptions of this site are shown in Figures 1-5.
A schematic of the study area in Pool 8 is shown in Figure 1. This is a small portion of the pool.
The entire bathymetry of the reach was mapped during the first trip. In subsequent trips, only the
area between river miles (RM) 688.7 and 689.2 was mapped. The sediment transport and effects of
structures 54 and 55 will be monitored in this area.
DATA COLLECTION: Figure 6 shows a close-up of some results of the data collection in the
study area. The results of the trip 1 bathymetric survey are shown in the yellow-green-blue color
background. The bathymetric features are clearly visible. Sediment samples and static velocity
measurements were taken at the numbered locations. Additional swaths of bathymetric data were
acquired at four separate times on the same day. These are represented by the brown sections in
which points 7, 6, 5, and 2 are located.
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