ERDC/CHL CHETN-VII-5
December 2003
for each trip are near 40 tons per day. If it can be verified and adequately explained that the ∆q
computed by ISSDOT really does approach the transport rate for small ∆t, then these ISSDOT
values compare favorably with the transport function computed values. The second result of
importance is the consistency of the relative values of transport for trip 2 compared to those for
trip 4. All five functions show significantly more transport for the drawdown condition (trip 2) than
the normal pool condition (trip 4).
CONCLUSIONS: For the same set of hydraulic and sediment characteristics, both the ISSDOT
method of computing bed-load transport gradient and the analytic transport functions computed
transport gradients/rates between 40 and 800 tons per day through the study reach. In each method,
the lower values corresponded to the normal pool condition, and the higher transport values
corresponded to the drawdown conditions. Supporting these data, the sand budget analysis provided
an estimate of a mean daily transport rate of bed load between 275 to 550 tons per day. The transport
rates for this case would depend on the amount of bed material that could be proven to be in
suspension.
Three sets of bed-load transport measurement data have been presented. They were each computed
independently of one another. They also were derived using different methods. Yet all three methods
produced results that make sense and are within at least an order of magnitude of each other. These
data suggest the following conclusions regarding the Pool 8 drawdown of 2001. It appears the
observed drawdown did in fact have the effect of increasing the sediment mobilization within the
study reach. Additionally, it shows that the original structures as designed, and in conjunction with a
drawdown, continue to positively influence sediment movement in the reach. Conversely, as pool
levels are increased, the structures will have a diminishing effect in helping to mobilize sediment
through the reach. Through further monitoring to establish base transport rates, it might be possible
to project sediment movement before, during, and after such events. Equipped with this information,
river managers could more efficiently plan their dredging requirements for events such as the Pool 8
drawdown.
POINT OF CONTACT: Questions about this CHETN can be addressed to David D. Abraham
(601-634-2846), email: .
REFERENCES
Abraham, D. (2002). "Quantification of bed-load transport using multi-beam survey data and traditional methods,"
CHETN-VII-4, U.S. Army Engineer Research and Development Center, Vicksburg, MS.
Hendrickson, J. S. (2003). "Bed material budget for the St. Paul District Reach of the Upper Mississippi River, Anoka,
Minnesota to Guttenberg, Iowa," Internal Report, U.S. Army Engineer District, St. Paul, MN.
Hendrickson, J. S., and Hrdlicka, M. (2003). "Sediment transport monitoring for the Pool 8 water level drawdown,"
Internal Report, U.S. Army Engineer District, St. Paul, MN.
NOTE: The contents of this technical note are not to be used for advertising, publication,
or promotional purposes. Citation of trade names does not constitute an official endorsement
or approval of the use of such products.
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