ERDC/CHL CHETN-VII-5
December 2003
a. Prior bathymetric surveys in the study reach.
b. Bathymetric surveys before, during, and after the drawdown in the same reach.
c. Velocity fields of the entire cross section upstream, over, and downstream of the most
intrusive structures and at the inflow (RM 690) and outflow (RM 688) boundaries of the
study reach.
d. Static velocity profiles at several locations along the structures and their cross sections, and
at the inflow (RM 690) and outflow (RM 688) boundaries of the study reach.
e. Suspended sediment samples taken concurrently and at the same locations as the static
velocity profiles.
f. Bed material load measurements around the most intrusive structures and at the inflow and
outflow boundaries of the study reach. These were made with high-resolution multibeam
surveys at these cross sections over a space and time scale sufficient to capture any bed form
movements. The methodology to accomplish this task is dependent upon the existence of
dunes in the reach and their rate of migration.
and at the inflow and outflow boundaries of the study reach.
Methodology: Three methodologies to determine if net sediment movement occurred were used.
The first method used detailed bathymetric data taken in the vicinity of RM 689.2. These data were
analyzed using a new method for computing the bed-load transport presently called ISSDOT
(Integrated-Section Surface Difference Over Time). The second method made use of long-term data
collected by the St. Paul District. This data included suspended sediment measurements and
bathymetric data. It was analyzed in the form of a sediment budget and through GIS manipulation.
The third method used measured sediment and hydraulic data. It was analyzed using sediment
transport functions.
Analysis Using ISSDOT: The measurement of suspended sediment fluxes is well established in
theory and practice. The measurement of bed material load in large sand bed streams and rivers has
been practically nonexistent. The Helley-Smith bed material load sampler has been shown to be
somewhat effective in small streams and for gravel and cobble, but not in large sand bed streams.
Dutch researchers at the University of Utrecht have also developed a sampler that shows promise for
use in large sand bed rivers, but has not been thoroughly tested on rivers like the Mississippi. Thus,
until this time, the ability to measure bed-load transport in large sand bed rivers has been elusive.
Knowing this, a new method for measuring bed-load transport using multibeam data was developed
as a part of this work unit. For more information on this new method (called ISSDOT, (Integrated
Section, Surface Difference Over Time)), see Abraham (2002).
Verification of the ISSDOT method is ongoing at this time through flume studies and comparison to
any standard techniques that are applicable. The method's validity as a measure of absolute values of
transport rates is still in the experimental phase. Also, questions have been raised as to whether a
transport rate or gradient of transport is actually being calculated. In Abraham (2002) it was termed
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