ERDC/CHL CHETN-VII-5
December 2003
at this volume or greater on an annual basis, so the volume change analysis didn't indicate signifi-
cant change.
2001 to 2002 time period
The volume change analysis also showed that between 2001 and 2002, over 40,000 cu yd of depo-
sition occurred between RM 690 and 691. From RM 687 to 688 and RM 689 to 690 about 10,000 cu
yd of deposition occurred in each reach. No dredging was needed in the study reach during this time
period.
2002 to 2003 time period
Between 2002 and 2003, over 20,000 cu yd of erosion occurred in the reach between RM 690 and
691. The dredging that was done in this reach, was done after the 2003 survey, so whatever caused
the erosion was not related to dredging. No other significant main channel volume changes occurred
during this time period.
These are interesting results because this entire reach usually aggrades due to the spring floods and
yet there was little change in main channel bathymetry. As previously described, the hydrodynamic
conditions in Pool 8 during the drawdown (which occurred in the summers of 2001 and 2002) should
have resulted in increased sediment transport, and perhaps this is what kept the channel from
aggrading.
The results of this GIS analysis cover time spans of 3 to 4 years and a river length of 8 km (5 miles).
Therefore, it cannot be used to say anything definitive as to whether or not the drawdown affected
local and temporary transport rates. What it does indicate is that the regular cycles of scour,
deposition and dredging may have been shifted towards erosion with less dredging. In the context of
the ISSDOT measurements, it allows that there certainly could have been increased transport during
the drawdown period, but that such an increase, and the effects from it, was only temporary.
Transport Function Analysis: Analytic transport functions are another way to estimate bed-
load transport in large sand-bed rivers. Many functions have been developed for a variety of
different river and flume conditions. These functions also compute different types of transport. For
instance, some compute only total sediment load, others bed material load, and yet others bed load
only. The sediment and hydraulic analysis package SAM, see Thomas et al. (2002),1 developed at
the ERDC Vicksburg, was used to run the transport functions selected for this project. SAM can be
accessed at the following Web site. http://chl.wes.army.mil/software/sam/. SAM is a windows based
package that allows users to select up to 20 different transport functions. These functions have been
programmed to accept the required and necessary hydraulic and sediment input data for each
function. When executed with the appropriate data, each selected function will output its computed
transport rate. Those functions that require the use of special graphs, for example Einstein's bed-load
function, have them analytically programmed into the package. For the Pool 8 study, 17 of the
functions were run, although only five of these can be used to compute bed load. Seventeen
functions were run because for one, it is very easy to run them once the sediment and hydraulic data
1
W. A. Thomas, R. R. Copeland, and D. N. McComas. (2002). "SAM hydraulic design package for channels,"
unpublished report, U.S. Army Engineer Research and Development Center, Vicksburg, MS.
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