Abstract
Velocimetric surveys were made by the U.S. Geological
Survey in 2011 and 2012 to provide data for the U.S. Army
Corps of Engineers’ ongoing study of bed degradation in
the Lower Missouri River. Using Acoustic Doppler Current
Profile technology, velocity data were collected at 87 river
miles along the Lower Missouri River from Rulo, Nebraska
to Waverly, Missouri, from July to October 2011 and in July
2012, for a total of 118 velocimetric surveys. Multiple-repeat
velocimetric surveys were done eight times at three river miles
from July to October 2011. Synoptic velocimetric surveys
spanning 2–4 days were done twice at ten river miles, once in
July 2011 and once in October 2011. Additional synoptic velocimetric
surveys were done at proximal river miles in October
2011 and July 2012. Main-channel, near-bed, near-bank,
and whole-river velocities were extracted from the Acoustic
Doppler Current Profile data using AdMap and compiled as
an average of reciprocal pairs for each survey. In addition, the
mean velocity computed by the Winriver II software for each
survey was integrated with the extracted data.
Multiple-repeat velocimetric surveys in the vicinity of
Kansas City and Waverly, Missouri, in 2011 indicated that
main-channel, near-bed, near-bank, and whole-river velocities
generally declined with respect to declining daily mean
discharges at the St. Joseph and Waverly, Missouri streamgaging
stations. Statistical analysis of the four extracted velocity
types indicated that multiple-repeat velocimetric surveys
were strongly correlated with daily mean discharges at nearby
streamgaging stations (coefficient of determination greater
than 0.75). Main-channel velocity exceeded whole-river velocity
by an average of 25 percent at river mile 357.70, 22 percent
at river mile 357.09, and 6.8 percent at river mile 290.20 for
all velocimetric surveys at each location, respectively. Mainchannel,
near-bed, near-bank, and whole-river velocities
declined about 48 percent from July to October 2011 at the
Kansas City sites and about 38 percent at the Waverly site.
Winriver II mean velocity from multiple-repeat velocimetric
surveys indicated that the relation between all velocities was
inconsistent from July to October 2011. Percent changes in
channel width from July to October 2011 were typically less
than concurrent changes in channel area and instantaneous
discharge. The combined synoptic and multiple-repeat survey
data for July 2011 did not indicate a clear longitudinal trend
of velocity as instantaneous discharge increased downstream.
Main-channel velocity exceeded whole-river velocity by an
average of 22 percent during July 2011 and in some cases by
more than 40 percent (river miles 452.50 and 308.80). Evaluation
of 10 pairs of synoptic and synoptic-repeat velocimetric
surveys with multiple-repeat velocimetric surveys from July
to October 2011 indicated that all velocity types and channel
width decreased by about one-third. Channel area and instantaneous
discharge decreased by more than 50 percent from
July to October 2011 and the percent by which main-channel
velocity exceeded whole-river velocity decreased slightly
from 22 percent in July to 19 percent. Comparing high (July
2011) to low (October 2011) discharge, where the channel
width and area expanded by a factor of nearly 3.0 or more at
high discharge (river miles 492.38 to 452.50), main-channel,
near-bed, near-bank, and whole-river velocities increased by
factors in the range of 1.1 to 1.7 and Winriver II mean velocity
decreased. At the Kansas City river miles, all velocity
types and channel areas nearly doubled at high discharge and
channel widths remained similar to those at low discharge.
Multiple-repeat and synoptic velocimetric surveys evaluated
in October 2011 indicated that main-channel, near-bed, nearbank,
and whole-river velocities generally increased downstream
from river miles 424.20 to 404.70 and then decreased,
until river mile 290.20, where they increased slightly.
Of the July 2012 synoptic velocimetric surveys, velocities
near St. Joseph, Missouri, indicated no longitudinal trends
in the main-channel, near-bed, near-bank, and whole-river
velocities. The Kansas City and Waverly synoptic velocimetric
surveys indicated a general decrease in these velocities proceeding
downstream. For all 2012 surveys, near-bed velocity
was closest in magnitude to Winriver II mean velocity and
near-bed and whole-river velocities decreased with increasing
channel area. For the entire study, variations in near-bank
velocity may have been due to the influence of channel structures
and their diversion of higher velocities away from the
channel edges.