Research about Missouri;Nebraska

USGS2014

A velocimetric survey of the Lower Missouri River from river mile 492.38 to 290.20, July-October 2011 and July 2012

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.

Missouri;Nebraska↗

USGS2012

Bathymetric and velocimetric surveys at highway bridges crossing the Missouri River in and into Missouri during summer flooding, July-August 2011

Bathymetric and velocimetric surveys were conducted by the U.S. Geological Survey, in cooperation with the Kansas and Missouri Departments of Transportation, in the vicinity of 36 bridges at 27 highway crossings of the Missouri River between Brownville, Nebraska and St. Louis, Missouri, from July 13 through August 3, 2011, during a summer flood. A multibeam echo sounder mapping system was used to obtain channel-bed elevations for river reaches ranging from 1,350 to 1,860 feet and extending across the active channel of the Missouri River. These bathymetric scans provide a "snapshot" of the channel conditions at the time of the surveys and provide characteristics of scour holes that may be useful in the development of predictive guidelines or equations for scour holes. These data also may be used by the Kansas and Missouri Departments of Transportation to assess the bridges for stability and integrity issues with respect to bridge scour during floods. Bathymetric data were collected around every pier that was in water, except those at the edge of water, in extremely shallow water, or surrounded by debris rafts. Scour holes were present at most piers for which bathymetry could be obtained, except at piers on channel banks, those near or embedded in lateral or longitudinal spur dikes, and those on exposed bedrock outcrops. Scour holes observed at the surveyed bridges were examined with respect to depth and shape. Although exposure of parts of foundational support elements was observed at several piers, at most sites the exposure likely can be considered minimal compared to the overall substructure that remains buried in bed material; however, there were several notable exceptions where the bed material thickness between the bottom of the scour hole and bedrock was less than 6 feet. Such substantial exposure of usually buried substructural elements may warrant special observation in future flood events. Previous bathymetric surveys had been done at several of the sites, and comparisons between bathymetric surfaces from the previous surveys and those of this study indicate substantial variability in the response of the channel bed to the 2011 summer flood conditions. At sites in Kansas City, there was no consistent deepening of the channel or increase in the size of scour holes, despite substantially more discharge and a higher water-surface elevation in the 2011 surveys, which implies the high-flow conditions during the 2011 surveys created a similar scour scenario to the previous surveys. At Jefferson City and the St. Louis sites, there was a consistent deepening of the channel, and a slight to substantial increase in the depth of scour holes in the 2011 surveys compared to previous surveys, although the effects of the higher flow appeared to be mitigated by the shape and alignment of the piers at most sites in St. Louis. Construction activities related to a new bridge at the Atchison, Kansas, site likely have contributed to the substantial additional scour observed there in a previous survey during the 2010 flooding, and the subsequent aggradation of the channel bed observed in the 2011 survey. Pier size, nose shape, and alignment to flow also had a profound effect on the size of the scour hole observed for a given pier.

Missouri;Nebraska↗