The purpose of this report is to document the results of bathymetric and velocimetric surveys completed August 13–14, 2019, of the Missouri River channel near 9 highway bridges at 8 crossings in the Kansas City, Mo., area (fig. 1; table 1) using an MBMS and an acoustic Doppler current profiler (ADCP). Special bathymetric surveys before and after installation of scour countermeasures near the main channel pier of two of the sites in August and October 2020 also are documented. Equipment and methods used and results obtained are described. The results obtained from the bathymetric and velocimetric surveys of the channel document the channel-bed conditions and velocity distribution at the time of the surveys and provide characteristics of scour holes that may be useful in developing predictive guidelines or equations for scour holes. These data also may be used by MoDOT as a low to moderate flood-flow comparison to help assess the bridges for stability and integrity issues with respect to bridge scour. Comparison of results to previous surveys at the sites (Huizinga, 2010, 2012, 2016, 2020a) also are provided.

The study area for this report is the Missouri River in and near Kansas City, Mo. (fig. 1). The Missouri River flows through the Kansas City area from west to east, meandering across the floodplain. The river is highly channelized in the Kansas City area; rock revetment and spur dikes are along the banks to maintain the channel alignment, and levees and floodwalls are on the upper banks to limit flooding in the industrial, commercial, and agricultural areas on the floodplains. The site numbering sequence used in Huizinga (2012) is used in this report for consistency and comparability.

Data from the streamflow-gaging station (hereinafter referred to as “streamgage”) on the Missouri River at Kansas City, Mo. (station 06893000; U.S. Geological Survey, 2020; fig. 1), indicated the Missouri River was in a trough between minor flood rises when the sites were surveyed August 13–14, 2019 (fig. 2A); however, the trough happened during generally higher summer streamflows that lasted from mid-March to past the end of the water year in September (fig. 2B). Moderate streamflows of more than 110,000 cubic feet per second (ft³/s) were observed throughout the spring and summer, compared to 45,000–50,000 ft³/s observed during the late winter trough in early March. The streamflow on the Missouri River as measured at the Kansas City streamgage ranged from about 122,000 to 137,000 ft³/s during the surveys. This streamflow range has a daily exceedance range of about 5 to 6 percent (U.S. Geological Survey, 2021) and is slightly less than the 50-percent annual exceedance probability (2-year recurrence interval) flood of 142,000 ft³/s (U.S. Army Corps of Engineers, 2004, plate E–20). Daily exceedance probabilities were computed using daily streamflow from 1957 to 2020 (U.S. Geological Survey, 2021).

Streamflow conditions in these daily and annual exceedance ranges are in the low to moderate flood-flow regime. In an analysis of real-time scour monitoring data at Jefferson City, Mo., Huizinga (2014) noted that substantial pier scour begins soon after the onset of hydrograph rise (substantial rise of 8 feet [ft] or more), although the scour often does not reach maximum depth until the peak stage is reached or sometime thereafter (see fig. 35 in Huizinga, 2014). Although the streamflow conditions during these surveys was not at the peak streamflow for the summer season, several peaks had occurred earlier in the year (fig. 2), and streamflow was substantially higher than base flow based on the daily exceedance values. Furthermore, the peak streamflow of 308,000 ft³/s on June 2, 2019, a streamflow that is in the 2- to 5-percent annual exceedance probability (20- to 50-year recurrence interval) range (U.S. Army Corps of Engineers, 2004, plate E–20), was the highest streamflow since 1993 and is higher than flows observed in 2011 (U.S. Geological Survey, 2020). Although the scour scenario captured at the sites in this study likely does not represent the maximum scour potential that might have been observed immediately after the peak streamflow in early June, the cumulative information gathered at the sites during the course of multiple surveys in 2010, 2011, 2016, and 2019 remains useful for determining scour for a variety of streamflow conditions and flood durations.

Special surveys were conducted at two of the sites in August and October 2020. The streamflow on the Missouri River as measured at the Kansas City streamgage was about 61,000 ft³/s during the survey on August 17, 2020, and was about 46,200 ft³/s during the survey on October 23, 2020. These streamflows have a daily exceedance of about 35 and 55 percent, respectively (daily exceedance probabilities were computed using daily streamflow from 1957 to 2020; U.S. Geological Survey, 2021), and are substantially less than the 50-percent annual exceedance probability (2-year recurrence interval) flood of 142,000 ft³/s (U.S. Army Corps of Engineers, 2004, plate E–20). Streamflow conditions in these daily and annual exceedance ranges are in the nonflood regime.

The bathymetry of the Missouri or Mississippi River at each of the bridges was determined using a high-resolution MBMS. The various components of the MBMS used for this study are as described in reports about studies on the Missouri and Mississippi Rivers in Missouri (Huizinga, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017a; 2020a, e; Huizinga and others, 2010) and on the Missouri and Yellowstone Rivers in North Dakota (Densmore and others, 2013). The survey methods used to obtain the data were similar to these previous studies, as were the measures used to ensure data quality. A brief description of the equipment follows; a more-complete description of the various system components and methods used in this study are available in the previous reports by Huizinga (2010), Huizinga and others (2010), and Densmore and others (2013).

An MBMS is an integration of several individual components: the multibeam echosounder (MBES), an inertial navigation system (INS), and a data-collection and data-processing computer. The MBES that was used for the 2019 surveys is the Norbit iWBMSh (fig. 3), which operated at a frequency of 400 kilohertz (kHz). The iWBMSh is similar in operation to the MBES systems used in other previous studies in the Kansas City area, except that it has a curved receiver array, which enables bathymetric data to be collected throughout a sound navigation and ranging (sonar) swath range of 210 degrees. Optimum data usually are collected in a swath of less than 160 degrees (80 degrees on each side of nadir, or straight down below the MBES); nevertheless, the swath can be electronically rotated to either side of nadir, enabling data along sloping banks to be captured up to a depth just below the water surface. The Norbit iWBMSh has a tightly coupled INS, the Applanix Position Orientation Solution for Marine Vessels (POS MV) OceanMaster system, consisting of an inertial motion unit on the sonar head (fig. 3A) and two Global Navigation Satellite System (GNSS) antennae. The INS provides position in three-dimensional space and measures the pitch, roll, yaw, and heading of the vessel (and, thereby, the MBES) to accurately position the data received by the MBES. Real-time kinematic (RTK) differential corrections for the INS came from cellular communication with the MoDOT GNSS real-time network for the navigation and tide solution during the 2019 surveys.

As in previous surveys (Huizinga, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017a, b, 2020a, b, c, d, e), the navigation information from the 2019 surveys was postprocessed using the POSPac Mobile Mapping Suite (MMS) software (Applanix Corporation, 2017) to mitigate the effects of degraded positional accuracy of the vessel while near or under a bridge. The POSPac MMS provides tools to identify and compensate for sensor and environmental errors and computes an optimally blended navigation solution from the GNSS and inertial measurement unit (IMU) raw data. The blended navigation solution (called a “smoothed best estimate of trajectory” or “SBET” file) generated by postprocessing the navigation data was applied to the survey at a given bridge to minimize the effects of the GNSS outages while surveying under the bridges.

The data from the MBES and INS components were processed and integrated into a cohesive dataset for cleanup and visualization. A computer onboard the survey vessel ran the HYPACK/HYSWEEP data acquisition software (HYPACK, Inc., 2018) that was used to prepare for the bathymetric surveys and collect the survey data. After completing the surveys, the acquired depth data were further processed to remove data spikes and other spurious points in the multibeam swath trace, georeferenced using the navigation and position solution data from the SBET file from the POSPac MMS, and visualized in HYPACK/HYSWEEP as a gridded bathymetric surface or a point cloud.

Information about the velocity of the river at various points throughout each study reach were collected using an ADCP, similar to recent previous studies by Huizinga (2012, 2013, 2014, 2015, 2016, 2017a, b, 2020a, b, c, d, e). A Teledyne RD Instruments Rio Grande ADCP operating at 600 kHz was used to obtain velocities at 1.64-ft increments, or “bins,” throughout the water column. The Rio Grande 600-kHz ADCP operates in depths from 2.3 to 230 ft and determines the velocity of the water by measuring the Doppler shift of an acoustic signal reflected from various particles suspended in the water (Mueller and others, 2013). By measuring the Doppler shift in four different beam directions, the velocity of the water in each bin can be determined in three dimensions.

The methods used to acquire and ensure the collection of quality data were the same as those used in previous studies using the MBES (methods are detailed in Huizinga and others, 2010; Huizinga, 2010, 2012). A brief summary of—and differences from—these methods are highlighted below.

Structure A1800 (site 6; table 1) on Interstate 635 crosses the Missouri River at river mile (RM) 374.1, on the northwestern side of Kansas City (fig. 1). The site was surveyed on August 13, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GNSS tide solution, was 731.9 ft (table 5; fig. 6). Streamflow on the Missouri River was about 112,000 ft³/s during the survey (table 5).

The survey area was about 1,640 ft long and averaged about 755 ft wide, extending across the active channel from bank to bank (fig. 6). The upstream end of the survey area was about 770 ft upstream from the centerline of structure A1800 (fig. 6). The channel-bed elevations ranged from about 698 to 719 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 7). A thalweg along the outside of the channel bend on the right (south) bank was about 15 ft deeper than the channel bed on the inside of the bend on the left (north) bank (fig. 6). Several medium to large dune features were detected in the middle of the channel along the left side of the thalweg, and the left (north) side and thalweg on the right (south) side were covered with numerous small dunes and ripples (fig. 6). As in previous surveys (Huizinga, 2010, 2012, 2016), a rock outcrop and stone revetment were present on the right (south) bank throughout the reach (fig. 6).

The scour hole near main channel pier 3 had a minimum channel-bed elevation of about 692 ft (table 6), about 18 ft below the average channel bed immediately upstream from the pier (the value of the “depth of scour hole from upstream channel bed” in table 6; fig. 6), and about 10 ft below the elevation of the bottom of the pier seal course of 702.28 ft (fig. 8; table 6). Information from bridge plans indicates that pier 3 is founded on shafts drilled 20 ft into bedrock, and about 40 ft of bed material are between the bottom of the scour hole and bedrock at the upstream face of pier 3 (fig. 8; table 6).

The difference between the survey on August 13, 2019, and the previous nonflood survey on June 2, 2015 (fig. 9), indicates about 73 percent of the joint area of interest had detectable change, which means about 27 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation seemed about equal between scour and deposition in the middle part of the channel from 2015 to 2019 in the DoD map; however, in the thalweg downstream from the bridge and along the left (north) bank throughout the reach, scour is dominant (fig. 9). The average difference between the bathymetric surfaces (the statistical mean value of the gridded raster surface [fig. 9] created from the difference between the 2019 and 2015 gridded raster bathymetric surfaces) was –1.59 ft (table 7), indicating moderate channel degradation between the 2015 and 2019 surveys. The net volume of cut in the reach from 2015 to 2019 was about 72,900 cubic yards (yd³), and the net volume of fill was about 20,900 yd³, resulting in a net loss of about 52,000 yd³ of sediment between 2015 and 2019. The cross sections from the two surveys along the upstream face of the bridge are not substantially different from one another for most of the cross section, except near the left bank where the 2019 section is substantially lower than all the previous sections (fig. 8). The frequency distribution of bed elevations in 2019 also was similar to 2015 but with a higher percentage of cells at lower channel-bed elevations (fig. 7). The scour hole near pier 3 was of a very similar shape in 2019 and 2015 (fig. 8), as evidenced by the overall area of “no data” or minimal change around the pier (fig. 9). The rock outcrop on the right (south) bank showed signs of minor scour upstream from the bridge (fig. 9). Although rock ultimately is an erodible material, its rate of erosion is substantially slower than that of sand and silt (Arneson and others, 2012). The stone revetment on the downstream right (south) bank showed no signs of substantial change (fig. 9). Substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 13, 2019, and the previous flood survey on July 16, 2011 (fig. 10), indicates about 85 percent of the joint area of interest had detectable change, which means about 15 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial bed variation is apparent from 2011 to 2019 in the DoD map, particularly near the thalweg where large dune features were present in the 2011 survey (Huizinga, 2012). Whereas scour of as much as 15 ft seems dominant on the left (north) side of the channel in the DoD map, deposition of as much as 10 ft seems dominant in the thalweg (fig. 10). The average difference between the bathymetric surfaces was –1.77 ft (table 7), indicating moderate net channel degradation between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 110,500 yd³, and the net volume of fill was about 43,500 yd³, resulting in a net loss of about 67,000 yd³ of sediment between 2011 and 2019. As with the 2015 survey, the cross sections from the two surveys along the upstream face of the bridge are not substantially different from one another for most of the cross section, except near the left bank where the 2019 section is substantially lower than all the previous sections (fig. 8). The frequency distribution of bed elevations in 2019 also was similar in shape but narrower to 2011, and had a higher percentage of cells at the middle channel-bed elevations (fig. 7). As with the 2015 survey, the scour hole near pier 3 was of a very similar shape in 2019 and 2011 (fig. 8), again as evidenced by the overall area of “no data” or minimal change around the pier in the DoD map (fig. 10). The rock outcrop on the right (south) bank showed signs of more substantial scour upstream from the bridge, and the stone revetment on the downstream right (south) bank showed signs of minor scour (fig. 10). As with the previous DoD map, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 13, 2019, and the earliest nonflood survey on March 15, 2010 (fig. 11), indicates about 87 percent of the joint area of interest had detectable change, which means about 13 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Scour is dominant throughout most of the reach between 2010 and 2019 in the DoD map, except near some dune features present in the middle of the channel in 2010 and near pier 3 (Huizinga, 2010; fig. 11). The average difference between the bathymetric surfaces was –2.93 ft (table 7), indicating substantial channel degradation between the 2010 and 2019 surveys. The net volume of cut in the reach from 2010 to 2019 was about 122,700 yd³, and the net volume of fill was about 20,500 yd³, resulting in a net loss of about 102,200 yd³ of sediment between 2010 and 2019. Whereas the cross sections from the two surveys along the upstream face of the bridge are not substantially different from one another for most of the cross section, as with all the surveys the 2019 section is substantially lower than all the previous sections near the left bank (fig. 8). The frequency distribution of bed elevations in 2019 was very similar to 2010 for elevations below about 708 ft; however, above the 2019 distribution has a higher percentage of cells at a lower channel-bed elevation than 2010 (fig. 7). The scour hole near pier 3 was deeper and wider in 2010 than in 2019 (fig. 8), as evidenced by large horseshoe-shaped area of deposition around the pier in the DoD map (fig. 11). The rock outcrop on the right (south) bank showed signs of moderate scour upstream from the bridge, and the stone revetment on the downstream right (south) bank showed signs of minor scour (fig. 11). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The vertically averaged velocity vectors indicate mostly uniform flow throughout the reach (fig. 12). A maximum velocity of about 11 feet per second (ft/s) was present in the thalweg immediately upstream from the bridge, and a minimum of 3 ft/s was present along the inside of the bend on the left (north) bank (fig. 12). The wake vortices downstream from pier 3 were not pronounced and seemed to be no greater than the general nonuniformity of flow observed in the channel (fig. 12). Minor turbulence was present in all the sections (fig. 12).

Structure A8340 (site 7; table 1) on U.S. Highway 69 crosses the Missouri River at RM 372.6, on the northwestern side of Kansas City (fig. 1). The site was surveyed on August 13, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GNSS tide solution, was 730.6 ft (table 5; fig. 13). Streamflow on the Missouri River was about 114,000 ft³/s during the survey (table 5).

The survey area was about 1,550 ft long and averaged about 875 ft wide, extending across the active channel from bank to bank (fig. 13). The upstream end of the survey area was about 680 ft upstream from the centerline of structure A8340 (fig. 13). The channel-bed elevations ranged from about 698 to 717 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 14), except near the central main channel bent 4 of structure A8340 (fig. 13). There was a defined thalweg along the toe of the right (south) bank, which was about 12 ft deeper than the channel bed in the middle of the channel (fig. 13). A series of medium dunes was present in the middle of the channel, and numerous other small dunes and ripples were present throughout the rest of the channel (fig. 13). As in previous surveys (Huizinga, 2010, 2012, 2020a), stone revetment was present on the right (south) bank throughout the reach, and two spur dikes were present on the left (north) bank (fig. 13). Partial remnants of the pier from old structure A0450 were evident to the right and downstream from bent 4 of structure A8340 (fig. 13).

A local scour hole near bent 4 had an approximate minimum channel-bed elevation of about 688 ft (table 6), the minimum elevation for the surveyed area (table 5), and about 17 ft below the average channel bed immediately upstream from the bent (table 6; fig. 13). A local scour hole near bent 5 had a minimum elevation of 707 ft, about 5 ft below the average channel bed immediately upstream from the pier (fig. 13; table 6). Bent 3 is surrounded by the rock revetment on the right (south) bank, but a very small depression of about 3 ft was present in the revetment near the upstream face of the upstream column (fig. 13; table 6). Information from bridge plans indicates that all the main channel bents of structure A8340 are shafts drilled about 23 to 28 ft into bedrock and have about 50 ft of bed material between the bottom of the scour hole and bedrock at bent 4 (fig. 15; table 6); bents 5 and 3 have about 69 and 82 ft of bed material between the bottom of the scour hole and bedrock, respectively (fig. 15; table 6).

The difference between the survey on August 13, 2019, and the previous nonflood survey on May 22, 2017 (fig. 16), indicates about 93 percent of the joint area of interest had detectable change, which means only 7 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation appears to be predominately scour from 2017 to 2019 in the DoD map, except downstream from the spur dikes and in the troughs of dunes present in the 2017 survey (Huizinga, 2020a; fig. 16). The average difference between the bathymetric surfaces was –1.90 ft (table 7), indicating moderate channel degradation between the 2017 and 2019 surveys. The net volume of cut in the reach from 2017 to 2019 was about 119,600 yd³, and the net volume of fill was about 33,900 yd³, resulting in a net loss of about 85,700 yd³ of sediment between 2017 and 2019. The cross sections from the two surveys along the upstream face of the bridge indicate a nearly uniform lowering of about 5 ft for most of the cross section (fig. 15). The frequency distribution of bed elevations in 2019 was similar in shape to 2017 but with a higher percentage of cells at lower channel-bed elevations (fig. 14). The scour holes near main channel bents 4 and 5 were of a very similar shape in 2019 and 2017 (fig. 15), as evidenced by the overall area of similar change around the bents in the DoD map (fig. 16). The stone revetment on the right (south) bank also showed signs of nearly uniform minor scour (fig. 16).

The difference between the survey on August 13, 2019, and the previous flood survey on July 16, 2011 (fig. 17), indicates about 88 percent of the joint area of interest had detectable change, which means about 12 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial bed variation is again apparent from 2011 to 2019 in the DoD map, with scour predominant throughout the reach except for substantial deposition at the former location of the old bridge piers near bent 4 and in the downstream thalweg and the troughs of dunes present in the 2011 survey (Huizinga, 2012). Whereas scour of greater than 10 ft appears dominant on the left (north) side of the channel in the DoD map, deposition of as much as 10 ft occurred in the thalweg, and deposition of more than 20 ft occurred downstream from the downstream spur dike (fig. 17). The average difference between the bathymetric surfaces was –2.27 ft (table 7), indicating substantial net channel degradation between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 137,700 yd³, and the net volume of fill was about 45,600 yd³, resulting in a net loss of about 92,100 yd³ of sediment between 2011 and 2019. As with the 2017 survey, the cross sections from the two surveys along the upstream face of the bridge indicate a nearly uniform lowering of 5 to 10 ft for most of the cross section except the location of the former pier (fig. 15). The frequency distribution of bed elevations in 2019 also was similar in shape but slightly narrower to 2011, with a higher percentage of cells at the middle channel-bed elevations (fig. 14). The differences in the frequency distribution of bed elevations in 2017 and 2019 from 2011 (fig. 14) likely are a direct result of the new bridge bents, which are designed to be more hydrodynamic and less scour-inducing than the old bridge piers. The stone revetment on the right (south) bank also showed signs of nearly uniform minor scour in the DoD map (fig. 17).

The difference between the survey on August 13, 2019, and the earliest nonflood survey on March 15, 2010 (fig. 18), indicates about 84 percent of the joint area of interest had detectable change, which means about 16 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation appeared about equal between scour and deposition from 2010 to 2019 in the DoD map, with scour predominant along the left (north) side of the channel and on the right (south) bank, and deposition predominant in the middle of the channel, particularly at the former location of the old bridge piers near bent 4, in the thalweg along the right (south) bank, and in the troughs of dunes present in the 2010 survey (Huizinga, 2010; fig. 18). The average difference between the bathymetric surfaces was +1.33 ft (table 7), indicating moderate channel aggradation between the 2010 and 2019 surveys. The net volume of cut in the reach from 2010 to 2019 was about 57,100 yd³, and the net volume of fill was about 100,900 yd³, resulting in a net gain of about 43,800 yd³ of sediment between 2010 and 2019. The cross sections from the two surveys along the upstream face of the bridge are substantially different from one another for most of the left side and become more similar to one another about midway between bents 3 and 4 (fig. 15). The frequency distribution of bed elevations in 2010 was somewhat unique compared to the other surveys, but the 2019 distribution was similar to 2010, except with a lower percentage of cells at a lower channel-bed elevation than 2010 (fig. 14). As noted in the previous paragraph, the differences in the frequency distribution of bed elevations in 2017 and 2019 from 2011 and 2010 (fig. 14) likely are a direct result of the new bridge bents, which are designed to be more hydrodynamic and less scour-inducing than the old bridge piers. As with all the DoD maps for this site, stone revetment on the right (south) bank also showed signs of nearly uniform minor scour (fig. 18).

The vertically averaged velocity vectors indicate mostly uniform flow throughout the reach (fig. 19). A maximum velocity of about 10 ft/s was present in the upstream middle of the channel, and a minimum velocity of about 1 ft/s was present with flow reversal downstream from the various spur dikes in the reach (fig. 19). Minimal effect on the velocity was observed downstream from bent 4 (fig. 19), indicating the new pier design is appropriately hydrodynamic. Minor turbulence was present in all the sections (fig. 19).

Structure A4649 (site 8; table 1) on U.S. Highway 169 crosses the Missouri River at RM 366.2, immediately north of downtown Kansas City, Mo. (fig. 1). The site was surveyed on August 13, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GNSS tide solution, was 729.0 ft (table 5; fig. 20). Streamflow on the Missouri River was about 126,000 ft³/s during the survey (table 5).

The survey area was about 1,660 ft long and averaged about 910 ft wide, extending from bank to bank in the main channel (fig. 20). The upstream end of the survey area was about 720 ft upstream from the centerline of structure A4649 at pier 2 (fig. 20). The channel-bed elevations ranged from about 689 to 719 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 21), except near pier 2 of structure A4649, the various railroad bridge piers, and the concrete nose upstream from the railroad bridge turntable pier (fig. 20). A deep thalweg on the right (south) bank on the upstream end of the surveyed area was about 20 ft deeper than the channel bed in the middle of the channel (fig. 20). The thalweg became shallower and shifted to the left at the bridges and downstream (fig. 20). As in previous surveys at this site (Huizinga, 2010, 2012, 2016), remnants of piers from an old bridge were evident downstream from the existing railroad bridge (fig. 20). Numerous medium and small dunes and ripples were detected throughout the channel, with slightly larger features in the channel thalweg upstream from structure A4649 and on the left side of the channel downstream from the railroad bridge (fig. 20). Also as in previous surveys, stone revetment was present on the right (south) bank throughout the reach (fig. 20).

A scour hole near main channel pier 2 (fig. 20) had a minimum channel-bed elevation of about 678 ft (table 6), about 24 ft below the average channel bed immediately upstream from the pier (table 6). As in previous surveys at this site (Huizinga, 2010, 2012, 2016), the scour hole was more extensive around the right (south) side of the pier, with a submerged remnant of a structure near the left (north) downstream side of the pier (figs. 20 and 1.3A), presumably a nose for the railroad bridge downstream similar to the concrete nose upstream from the railroad bridge turntable pier. Also, as in the previous surveys at this site, the remnants of the old railroad bridge piers were clearly defined, as were the piles of particulate rock debris around them. The remnant bridge pier downstream from the existing railroad bridge turntable pier had a maximum elevation of about 710 ft, which is about 13 ft above the channel bed immediately upstream from it and about 19 ft below the water surface at the time of the 2019 survey. Avoidance of this pier remnant might be difficult for large vessels in flow conditions lower than those on the day of the survey. The overall minimum channel-bed elevation was 676 ft (table 5) and was observed upstream from the left railroad bridge pier downstream from pier 2 of structure A4649. Information from bridge plans indicate that the main channel pier 2 of structure A4649 is a caisson on bedrock, and has about 8 ft of bed material between the bottom of the scour hole and the bottom of the caisson (fig. 22; table 6).

The difference between the survey on August 13, 2019, and the previous nonflood survey on June 2, 2015 (fig. 23), indicates about 99 percent of the joint area of interest had detectable change, which means only 1 percent of the differences in the joint area of interest are equivocal and within the uncertainty. However, bed variation seems about equal between scour and deposition throughout the channel from 2015 to 2019 in the DoD map because deposition on the upstream left (north) side is balanced with scour in the middle (fig. 23). The average difference between the bathymetric surfaces was –0.13 ft (table 7), indicating minimal channel degradation between the 2015 and 2019 surveys. The net volume of cut in the reach from 2015 to 2019 was about 74,200 yd³, and the net volume of fill was about 67,000 yd³, resulting in a net loss of about 7,200 yd³ of sediment between 2015 and 2019. The cross sections from the two surveys along the upstream face of the bridge are similar (fig. 22); there is deposition on the left end of the section and there is nearly uniform lowering of about 5 ft for most of the rest of the cross section. The frequency distribution of bed elevations in 2019 was wider than 2015 because a higher percentage of cells are at lower and higher channel-bed elevations (fig. 21). The scour hole near main channel pier 2 was of a similar shape in 2019 and 2015 (fig. 22) but slightly deeper on the right (south) side as evidenced by the area of scour around that side of the pier in the DoD map (fig. 23). The stone revetment and bedrock outcrops on the right (south) bank showed signs of nearly uniform minor deposition throughout the surveyed reach (fig. 23). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 13, 2019, and the previous flood survey on July 17, 2011 (fig. 24), indicates about 83 percent of the joint area of interest had detectable change, which means about 17 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial bed variation is apparent from 2011 to 2019 in the DoD map, and scour was predominant throughout the reach except for moderate deposition in some localized scoured areas near the piers and the trough of a large dune present in the 2011 survey (Huizinga, 2012; fig. 24). The average difference between the bathymetric surfaces was –4.91 ft (table 7), indicating substantial net channel degradation between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 216,700 yd³, and the net volume of fill was about 6,000 yd³, resulting in a net loss of about 210,700 yd³ of sediment between 2011 and 2019. The cross sections from the two surveys along the upstream face of the bridge are substantially different except along the left side of the scour hole near pier 2 and on the right bank (fig. 22). The frequency distribution of bed elevations in 2019 was similar in shape to 2011 but with a higher percentage of cells at lower elevations than in 2011 (fig. 21). The stone revetment and bedrock outcrops on the right (south) bank showed signs of localized scour in the DoD map, but much of the difference on the tops of the bedrock outcrop was within the uncertainties of the data (fig. 24). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 13, 2019, and the earliest nonflood survey on March 16, 2010 (fig. 25), indicates about 74 percent of the joint area of interest had detectable change, which means about 26 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation seemed about equal between scour and deposition from 2010 to 2019 in the DoD map, deposition was predominant along the left (north) side of the channel, and scour was predominant along the right (south) side (fig. 25). The average difference between the bathymetric surfaces was +0.75 ft (table 7), indicating minor channel aggradation between the 2010 and 2019 surveys. The net volume of cut in the reach from 2010 to 2019 was about 45,200 yd³, and the net volume of fill was about 72,800 yd³, resulting in a net gain of about 27,600 yd³ of sediment between 2010 and 2019. The cross sections from the two surveys along the upstream face of the bridge are substantially different from one another for most of the section to the left of pier 2 and are more similar to one another to the right of pier 2 (fig. 22). The frequency distribution of bed elevations in 2019 was similar in shape but narrower than 2010 (fig. 21); however, the surveyed area was substantially wider in 2019 than in 2010 and extended higher on the channel banks. The stone revetment and bedrock outcrops on the right (south) bank showed signs of more substantial localized scour in the upstream reach in the DoD map, but much of the difference on the tops of the downstream bedrock outcrop was within the uncertainties of the data (fig. 25). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The vertically averaged velocity vectors indicate mostly uniform flow upstream from the structure A4649 ranging from a minimum of 2 ft/s along the inside of the bend on the upstream left (north) bank to a maximum velocity of about 10 ft/s in the channel thalweg along the outside of the bend on the right (south) bank, particularly near the bridges (fig. 26). Exceptions to uniform conditions include diagonal flows across the channel near structure A4649 (fig. 26), which may help explain the shift in the channel thalweg towards the left (north) bank through the reach. Substantial turbulence also was observed between structure A4649 and the railroad bridge and downstream from the railroad bridge piers (fig. 26). The rock piles near the right bank also appear to create turbulence (fig. 26).

The history of scour observed near pier 2 (Huizinga, 2010, 2012, 2016), and the nature of caisson foundations generally not being embedded in bedrock led MoDOT to install scour countermeasures around pier 2 during August–October 2020. Partial surveys of the channel bed near pier 2 of structure A4649 were done before and after installation of these scour countermeasures to document and verify installation. The historical scour hole near pier 2 was clearly evident in the pre-installation survey on August 17, 2020 (fig. 27), but the difference between the survey on August 13, 2019, and the partial survey on August 17, 2020, indicates moderate deposition of 5 to 10 ft had occurred from 2019 to 2020 (fig. 28). The cross sections from the two surveys along the upstream face of the bridge also indicates this deposition from 2019 to 2020 (fig. 22). The downstream edge of riprap blanket countermeasures installed around pier 2 was clearly evident in the post-installation survey on October 23, 2020 (figs. 29, 1.4B), and the difference between the pre- and post-installation surveys indicate the changes resulting from the installation (fig. 30). The net volume of cut in the partial reach from August 2019 to August 2020 was about 750 yd³, and the net volume of fill was about 18,660 yd³, resulting in a net gain of about 17,910 yd³ of sediment between August 2019 and August 2020 (fig. 28). However, the net volume of cut in the partial reach from August to October 2020 was about 6,300 yd³, and the net volume of fill was about 5,000 yd³, resulting in a net loss of about 1,300 yd³ of sediment between August and October 2020 (fig. 30), despite installation of the countermeasures. The scour hole was effectively mitigated, with as much as 20 ft of deposition near the pier (fig. 30), including some deposition of material on top of the blanket upstream from the bridge (fig. 29); nevertheless, moderate scour occurred in much of the partial reach around the riprap blanket between August and October (fig. 30).

Structure A4060 (site 9; table 1) on State Highway 9 crosses the Missouri River at RM 365.5, immediately north of downtown Kansas City, Mo. (fig. 1), and is about 3,400 ft downstream from structure A4649 (site 8) on U.S. Highway 169. The site was surveyed on August 13, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GPS tide solution, was 728.2 ft (table 5; fig. 31). Streamflow on the Missouri River was about 126,000 ft³/s during the survey (table 5).

The survey area was about 1,640 ft long and averaged about 900 ft wide, extending from bank to bank in the main channel (fig. 31). Piers 5 and 6 were in the water and away from the banks, and the upstream end of the survey area was about 665 ft upstream from the centerline of structure A4060 at pier 6 (fig. 31). The channel-bed elevations ranged from about 690 to 715 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 32), except near the railroad bridge pier upstream from pier 6 of structure A4060 (fig. 31). A shallow but wide thalweg along the right (south) side of the surveyed area was about 10 to 15 ft deeper than the channel bed in the middle of the channel (fig. 31). A few medium dune features were detected in the middle of the channel upstream from the bridges, and numerous smaller dunes and ripples were present throughout the channel reach (fig. 31). As in previous surveys (Huizinga, 2010, 2012, 2016), a stone revetment was present on the right (south) bank throughout the reach (fig. 31).

Erosion near the left (north) bank resulted in a scour hole near main channel pier 4 on that bank (figs. 31, 33) with a minimum channel-bed elevation of 699 ft (table 6). A scour hole near main channel pier 5 (fig. 31) had a minimum channel-bed elevation of about 692 ft (table 6), about 4 ft below the elevation of the bottom of the pier seal course of 696.26 ft (fig. 33; table 6). Near the right (south) main channel pier 6 (fig. 31), a scour hole had a minimum channel-bed elevation of about 687 ft (table 6), about 9 ft below the elevation of the bottom of the pier seal course of 696.26 ft (fig. 33; table 6). A substantially deeper scour hole was observed near the upstream railroad bridge pier (fig. 31), with a minimum elevation of about 678 ft, which is the overall minimum channel-bed elevation observed in this reach (table 5). This deeper hole likely was the result of flow around the upstream railroad pier combine with flow over large sheet piling panels that were lying on the channel bottom on the right (south) side of pier first observed in the 2010 survey (Huizinga, 2010), and seen in all subsequent surveys (Huizinga 2012, 2016). Information from bridge plans indicates that piers 4 through 6 are founded on shafts drilled 20 ft into bedrock, about 34 ft of bed material were between the bottom of the scour hole and bedrock at pier 4, about 25 ft of material were between the bottom of the scour hole and bedrock at pier 5, and about 17 ft of material were between the bottom of the scour hole and bedrock at pier 6 (fig. 33; table 6).

The difference between the survey on August 13, 2019, and the previous nonflood survey on June 3, 2015 (fig. 34), indicates about 81 percent of the joint area of interest had detectable change, which means about 19 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial bed variation is apparent from 2015 to 2019 in the DoD map, with scour predominant throughout the reach except along the left (north) side of the channel (fig. 34). The average difference between the bathymetric surfaces was –2.56 ft (table 7), indicating moderate to substantial degradation between the 2015 and 2019 surveys. The net volume of cut in the reach from 2015 to 2019 was about 143,100 yd³, and the net volume of fill was about 37,300 yd³, resulting in a net loss of about 105,800 yd³ of sediment between 2015 and 2019. The cross sections from the two surveys along the upstream face of the bridge also indicate these differences (fig. 33); there is localized scour near the left (north) bank, and there is nearly uniform lowering of about 10 ft between pier 6 and the right (south) bank. The frequency distribution of bed elevations in 2019 was wider than 2015, with a higher percentage of cells at lower and higher channel-bed elevations (fig. 32). The scour holes near main channel piers 5 and 6 were shallower on the left (north) side and deeper on the right (south) side of the pier as evidenced by the areas of deposition and scour near the piers in the DoD map (fig. 34). The scour of the left (north) bank near pier 4 also is clearly evident in the cross-section and DoD map (figs. 33, 34). The stone revetment on the right (south) bank showed signs of very minor localized deposition and scour throughout the surveyed reach (fig. 34); most of the differences on the right (south) bank were within the uncertainties of the data. As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 13, 2019, and the previous flood survey on July 17, 2011 (fig. 35), indicates about 90 percent of the joint area of interest had detectable change, which means about 10 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial bed variation is apparent from 2011 to 2019 in the DoD map, and scour is predominant throughout the reach except for moderate deposition in some localized scoured areas near the piers and in the channel downstream from the bridges in the 2011 survey (Huizinga, 2012; fig. 35). The average difference between the bathymetric surfaces was –3.64 ft (table 7), indicating substantial net channel degradation between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 186,100 yd³, and the net volume of fill was about 14,600 yd³, resulting in a net loss of about 171,500 yd³ of sediment between 2011 and 2019. The cross sections from the two surveys along the upstream face of the bridge show some similarities near and between piers 5 and 6 and on the right (south) bank, and are substantially different elsewhere (fig. 33). The frequency distribution of bed elevations in 2019 was similar in shape to 2011, but with a higher percentage of cells at lower elevations than in 2011 (fig. 32). The stone revetment on the right (south) bank showed signs of nearly uniform minor scour in the DoD map (fig. 35). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 13, 2019, and the earliest nonflood survey on March 16, 2010 (fig. 36), indicates about 85 percent of the joint area of interest had detectable change, which means about 15 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation seemed more equal between scour and deposition from 2010 to 2019 in the DoD map than in the other DoD maps, deposition was predominant along the left (north) side of the channel, and scour was predominant along the right (south) side (fig. 36). However, the average difference between the bathymetric surfaces was –1.58 ft (table 7), indicating minor to moderate channel degradation between the 2010 and 2019 surveys. The net volume of cut in the reach from 2010 to 2019 was about 109,900 yd³, and the net volume of fill was about 44,200 yd³, resulting in a net loss of about 65,700 yd³ of sediment between 2010 and 2019. The cross sections from the two surveys along the upstream face of the bridge are substantially different from one another for most of the section, except near pier 5 and the right (south) bank (fig. 33). The frequency distribution of bed elevations in 2019 was similar in shape but slightly wider than 2010 (fig. 32); however, the surveyed area was substantially wider in 2019 than in 2010 and extended higher on the channel banks. The stone revetment on the right (south) bank showed signs of more substantial localized scour in the upstream reach in the DoD map (fig. 36). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The vertically averaged velocity vectors indicate mostly uniform flow throughout the channel, ranging from about 1 to 9 ft/s (fig. 37). Exceptions to uniform conditions include substantial turbulence observed downstream from the railroad and highway bridge piers, and near the upstream left (north) bank (fig. 37).

Structure A7650 (site 10; table 1) on Interstate 35 crosses the Missouri River at RM 364.7, immediately north of downtown Kansas City, Mo. (fig. 1), and is about 4,300 ft downstream from structure A4060 on State Highway 9 (site 9). The site was surveyed on August 14, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GPS tide solution, was 728.2 ft (table 5; fig. 38). Streamflow on the Missouri River was about 142,000 ft³/s during the survey (table 5).

The survey area was about 1,640 ft long and averaged about 875 ft wide, extending from bank to bank in the main channel (fig. 38). The upstream end of the survey area was about 700 ft upstream from the centerline of structure A7650 at the main channel pylon (fig. 38). The channel-bed elevations ranged from about 690 to 714 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 39), except near the pylon and downstream from the spur dike on the downstream left (north) bank (fig. 38). The shallow thalweg in the channel at upstream structure A4060 diminished, such that there was no definitive thalweg along either side of the channel upstream from structure A7650 (fig. 38). Numerous small to medium dunes and ripples were present throughout the channel, and downstream translation of the smaller dunes and ripples between survey passes were more pronounced at this site than at the upstream sites (fig. 38). Downstream from the spur dike on the left (north) side of the downstream reach, the minimum channel-bed elevations of 671 ft was observed (fig. 38; table 5). As in previous surveys at this site (Huizinga, 2012, 2016), stone revetment was present on the right (south) bank throughout the reach, including the apparent slumped area near the downstream end of the reach observed in the previous survey (fig. 38).

As in previous surveys at this site (Huizinga, 2012, 2016), the main channel pylon seemed to be surrounded by a mound of rock riprap as a scour countermeasure, with a local minimum channel-bed elevation of about 677 ft near the downstream left (north) corner (fig. 38; table 6). The top of the riprap around the upstream face of the pylon was at an elevation of about 697 ft, which is slightly below the elevation of the bottom of the pylon seal course of 699.50 ft (table 6); the top of the riprap along the sides of the pylon is lower than at the upstream face (figs. 38 and 40). The minimum channel-bed elevation near the pylon was about 22 ft below the elevation of the bottom of the pylon seal course (fig. 38; table 6). Information from bridge plans indicates that the pylon is founded on shafts drilled 32 ft into bedrock, with about 30 ft of bed material between the bottom of the scour hole and bedrock (fig. 40; table 6).

The difference between the survey on August 14, 2019, and the previous nonflood survey on June 3, 2015 (fig. 41), indicates about 79 percent of the joint area of interest had detectable change, which means about 21 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation from 2015 to 2019 is moderate to substantial in the DoD map, and scour is predominant throughout the reach except small areas along the left (north) side of the channel and in the upstream right (south) part (fig. 41). The average difference between the bathymetric surfaces was –3.48 ft (table 7), indicating moderate to substantial degradation between the 2015 and 2019 surveys. The net volume of cut in the reach from 2015 to 2019 was about 141,200 yd³, and the net volume of fill was about 8,500 yd³, resulting in a net loss of about 132,700 yd³ of sediment between 2015 and 2019. The cross sections from the two surveys along the upstream face of the bridge are similar to each other but have uniform scour of about 5 ft between the pylon and the right (south) bank (fig. 40). The frequency distribution of bed elevations in 2019 was wider than 2015 because of a higher percentage of cells at lower channel-bed elevations (fig. 39). The scour hole near the main channel pylon was smaller and shallower upstream from the pylon but deeper downstream as evidenced by the areas of deposition and scour near the pylon in the DoD map (fig. 41). The rock riprap around the pylon base also indicated only minor differences, or differences within the uncertainty (fig. 41). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pylon footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section). The stone revetment on the right (south) bank showed signs of very minor localized deposition and scour, primarily downstream from the bridge (fig. 41); most of the differences on the right (south) bank were within the uncertainties of the data.

The difference between the survey on August 14, 2019, and the previous flood survey on July 17, 2011 (fig. 42), indicates about 74 percent of the joint area of interest had detectable change, which means about 26 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation appeared about equal between scour and deposition from 2011 to 2019 in the DoD map, with substantial scour downstream from the spur dike on the downstream left (north) side and in the upstream left (north) and downstream right (south) parts of the reach, and moderate to substantial deposition near the pylon and location of the old pier of structure L0734 (fig. 42). The average difference between the bathymetric surfaces was –1.29 ft (table 7), indicating minor to moderate degradation between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 86,900 yd³, and the net volume of fill was about 39,600 yd³, resulting in a net loss of about 47,300 yd³ of sediment between 2011 and 2019. The cross sections from the two surveys along the upstream face of the bridge show the substantial variation in the surveyed sections (fig. 40). However, the frequency distribution of bed elevations in 2019 was remarkably similar in shape to 2011 (fig. 39). The scour hole near the main channel pylon was smaller and shallower upstream from the pylon, as evidenced by the area of deposition near the pylon in the DoD map (fig. 42). The rock riprap around the pylon base indicated moderate differences (fig. 42), and the cross-section along the upstream bridge face shows the riprap has lowered by as much as 7 ft since 2011 (fig. 40). As with previous DoD maps, substantial deposition or scour apparent at the faces of the pylon footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section). The stone revetment on the right (south) bank showed signs of nearly uniform minor scour in the DoD map (fig. 42).

The vertically averaged velocity vectors indicate mostly uniform flow throughout most of the reach, with velocities ranging from about 2 to 8 ft/s (fig. 43). Exceptions to uniform conditions include flow reversal along the left (north) bank near the upstream tributary and in the pool downstream from the spur dike (fig. 43). Substantial turbulence also was observed downstream from the main channel pylon (fig. 43), likely as a result of the pylon being skewed to flow. The velocities do not seem to be higher near the bulge in the left bank at the bridge.

Structure A5817 (site 11; table 1) on State Highway 269 crosses the Missouri River at RM 362.3, northeast of downtown Kansas City, Mo. (fig. 1). The site was surveyed on August 14, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GPS tide solution, was 726.5 ft (table 5; fig. 44). Streamflow on the Missouri River was about 142,000 ft³/s during the survey (table 5).

The survey area was about 1,640 ft long and averaged about 995 ft wide, extending from bank to bank in the main channel (fig. 44). Piers 2 and 3 were in the water and away from the banks, and the upstream end of the survey area was about 670 ft upstream from the centerline of structure A5817 at pier 2 (fig. 44). The channel-bed elevations ranged from about 691 to 712 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 45). A moderately deep thalweg along the left (north) bank throughout the surveyed area contained evidence of bedrock exposure and was about 12 to 14 ft deeper than the channel bed in the middle of the channel (fig. 44). Numerous medium dune features were observed in the channel thalweg, and numerous medium to small dunes and ripples were present throughout the rest of the channel, decreasing in size towards the right (south) bank (fig. 44). As in previous surveys at this site (Huizinga, 2010, 2012, 2016), stone revetment and bedrock outcrops were present on the left (north) bank throughout the reach (fig. 44).

A scour hole near main channel pier 2 (fig. 44) had a minimum channel-bed elevation of about 687 ft (table 6), which was about level with the elevation of the bottom of the pier seal course of 687.26 ft (fig. 46; table 6). The top of the pier footing was evident during the survey (fig. 44). The minor scour hole near pier 3 was difficult to discern from nearby small dunes and ripples (fig. 44). Information from bridge plans indicates that piers 2 and 3 of structure A5817 are founded on shafts drilled 20 ft into bedrock, with about 10 ft of bed material between the bottom of the scour hole and bedrock at pier 2 and about 45 ft of material at pier 3 (fig. 46; table 6).

The difference between the survey on August 14, 2019, and the previous nonflood survey on June 3, 2015 (fig. 47), indicates about 89 percent of the joint area of interest had detectable change, which means about 11 percent of the differences in the joint area of interest are equivocal and within the uncertainty. There is moderate to substantial bed variation from 2015 to 2019 in the DoD map, with scour predominant throughout the middle of the reach, and deposition on both banks (fig. 47). The average difference between the bathymetric surfaces was –1.44 ft (table 7), indicating minor to moderate degradation between the 2015 and 2019 surveys. The net volume of cut in the reach from 2015 to 2019 was about 114,200 yd³, and the net volume of fill was about 40,800 yd³, resulting in a net loss of about 73, 400 yd³ of sediment between 2015 and 2019. The cross sections from the two surveys along the upstream face of the bridge are similar to each other but with uniform scour of 5 to 10 ft between the left (north) bank and pier 3 (fig. 46). The frequency distribution of bed elevations in 2019 was wider than 2015 because a higher percentage of cells were at lower and higher channel-bed elevations (fig. 45). The scour hole near the main channel pier 2 was deeper and wider than in 2015, as evidenced by the area of scour near that pier in the DoD map (fig. 47). Alternatively, the change from 2015 to 2019 near main channel pier 3 was equivocal to the uncertainty on the left side of the footing, and there was deposition along the right side (fig. 47). The bedrock outcrops and stone revetment on the left (north) bank showed signs of localized deposition throughout the reach between 2015 and 2019, which is somewhat unexpected (fig. 47); however, the differences on the tops of some of the outcrops were within the uncertainties of the data, which implies there may be a horizontal offset to the 2019 data on the bank that is creating the appearance of deposition.

The difference between the survey on August 14, 2019, and the previous flood survey on July 18, 2011 (fig. 48), indicates about 89 percent of the joint area of interest had detectable change, which means about 11 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial bed variation was apparent from 2011 to 2019 in the DoD map, with substantial scour throughout the reach except along the left (north) bank and in the troughs of substantial dunes present in the 2011 survey (Huizinga, 2012, fig. 48). The average difference between the bathymetric surfaces was –4.76 ft (table 7), indicating substantial degradation between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 268,900 yd³, and the net volume of fill was about 20,000 yd³, resulting in a net loss of about 248,900 yd³ of sediment in the reach between 2011 and 2019. The cross sections from the two surveys along the upstream face of the bridge show the substantial difference in the surveyed sections (fig. 46). The frequency distribution of bed elevations in 2019 also was substantially different from 2011 (fig. 45). The DoD map shows the substantial scour throughout the reach, so the scour hole near main channel pier 2 is indistinguishable from the overall change between 2011 and 2019 (fig. 48). As with the DoD map for 2015 to 2019 (fig. 47), the bedrock outcrops and stone revetment on the left (north) bank showed signs of localized deposition throughout the reach between 2011 and 2019, which is somewhat unexpected (fig. 48); however, the differences on the tops of the outcrops were again within the uncertainties of the data, which implies there may be a horizontal offset to the 2019 data on the bank that is creating the appearance of deposition.

The difference between the survey on August 14, 2019, and the earliest nonflood survey on March 17, 2010 (fig. 49), indicates about 80 percent of the joint area of interest had detectable change, which means about 20 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation seemed nearly equal between scour and deposition from 2010 to 2019 in the DoD map, deposition was predominant along the thalweg on the left (north) side of the channel, and scour was predominant along the middle and right (south) side (fig. 49). However, the average difference between the bathymetric surfaces was –1.38 ft (table 7), indicating minor to moderate channel degradation between the 2010 and 2019 surveys. The net volume of cut in the reach from 2010 to 2019 was about 111,500 yd³, and the net volume of fill was about 50,100 yd³, resulting in a net loss of about 61,400 yd³ of sediment between 2010 and 2019. The cross sections from the two surveys along the upstream face of the bridge are similar to each other but had deposition of 5 to 10 ft between the left (north) bank and pier 2 and scour of 5 to 10 ft between piers 2 and 3 (fig. 46). The frequency distribution of bed elevations in 2019 was different from 2010 because a higher percentage of cells was at lower channel-bed elevations (fig. 45); however, the surveyed area was substantially wider in 2019 than in 2010 and extended higher on the channel banks, particularly on the right (south) side (fig. 49). The bedrock outcrops and stone revetment on the left (north) bank showed signs of minor, localized deposition, particularly in the upstream reach in the DoD map (fig. 49); however, much of the differences on the left (north) side of the channel—and particularly the tops of the outcrops—were again within the uncertainties of the data, as would be expected. As with previous DoD maps, substantial deposition or scour is apparent at the faces of the pier footings resulting from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The vertically averaged velocity vectors indicate mostly uniform flow throughout the reach, ranging from about 3 ft/s along the inside of the bend on the right (south) bank to 9 ft/s in the thalweg along the left (north) bank (fig. 50). Exceptions to uniform flow include flows angled to the left (north) in the upstream part of the reach because of the bend in the channel (fig. 50). Moderate turbulence also was observed along the thalweg near the bedrock outcrops, along the inside of the bend along the right (south) bank, and downstream from pier 3 (fig. 50).

Structure A0767 (site 12; table 1) on Interstate 435 crosses the Missouri River at RM 360.3, on the northeastern side Kansas City, Mo. (fig. 1). The site was surveyed on August 14, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GPS tide solution, was 725.1 ft (table 5; fig. 51). Streamflow on the Missouri River was about 139,000 ft³/s during the survey (table 5).

The survey area was about 1,640 ft long and averaged about 930 ft wide, extending from bank to bank in the main channel (fig. 51). Piers 7 and 8 were in the water and away from the banks at structure A0767; however, as in previous surveys (Huizinga, 2010, 2012, 2016), pier 8 was immediately downstream from a spur dike and the upstream end of the pier was surrounded by a persistent substantial debris raft; however, bathymetric data could be obtained around the downstream end (fig. 51). A substantial and persistent sand bar also was present downstream from pier 8, as in previous surveys (Huizinga, 2010, 2012, 2016; fig. 51). The upstream end of the survey area was about 660 ft upstream from the centerline of structure A0767 at pier 7 (fig. 51). The channel-bed elevations ranged from about 682 to 711 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 52), except downstream from the tip of the spur dike and in the downstream reach near the rock outcrop on the left (north) bank (fig. 51). A shallow but wide thalweg was along the left (north) bank throughout the surveyed area, and became deeper in the downstream direction. The channel was filled with numerous medium dune features along the thalweg along the left (north) side of the channel and numerous small dunes and ripples throughout the rest of the channel, decreasing in size towards the banks (fig. 51). As in previous surveys at this site (Huizinga, 2010, 2012, 2016), stone revetment and bedrock outcrops were present on the left (north) bank throughout the reach (fig. 51).

The scour hole near main channel pier 7 (fig. 51) had a minimum channel-bed elevation of about 678 ft (table 6), which was about 11 ft below the elevation of the bottom of the pier seal course of 689.26 ft (fig. 53; table 6). The undermined seal course are evident in a shaded triangulated irregular network (TIN) image of the right (south) side of pier 7 (fig. 1.8). The upstream end of pier 8 was embedded in the rock spur dike and could not be surveyed because of the persistent substantial debris raft (fig. 51). The top of the footing on the downstream end of the pier was visible (fig. 51), but the minimum channel elevation adjacent to the pier footing was about 694 ft, which was about 5 ft higher than the bottom of the seal course elevation of 689.26 ft (table 6). Information from bridge plans indicates that piers 7 and 8 are founded on shafts drilled 20 ft into bedrock, with about 18 ft of bed material between the bottom of the scour hole and bedrock at pier 7 and about 46 ft of material at pier 8 (fig. 53; table 6). A substantial hole was present downstream from the tip of the spur dike, which contained the minimum channel elevation in the surveyed area of 668 ft (fig. 51; table 5); however, this hole was more than 50 ft away from pier 8, and substantial alluvial material was present between the hole and the pier.

The difference between the survey on August 14, 2019, and the previous nonflood survey on June 4, 2015 (fig. 54), indicates about 80 percent of the joint area of interest had detectable change, which means about 20 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation from 2015 to 2019 was moderate to substantial in the DoD map, deposition was predominant in the thalweg on the left (north) side, and scour was predominant throughout the middle and right (south) side of the reach (fig. 54). The average difference between the bathymetric surfaces was –4.17 ft (table 7), indicating substantial degradation between the 2015 and 2019 surveys. The net volume of cut in the reach from 2015 to 2019 was about 187,700 yd³, and the net volume of fill was only about 11,200 yd³, resulting in a net loss of about 176,500 yd³ of sediment between 2015 and 2019. The cross sections from the two surveys along the upstream face of the bridge indicate the trends from the DoD map, and deposition in the thalweg and scour was as much as 20 ft between pier 7 and the spur dike (fig. 53). The frequency distribution of bed elevations in 2019 appeared similar to 2015 but had a higher percentage of cells at lower channel-bed elevations than 2015 (fig. 52). The scour hole near main channel pier 7 was similar to that in 2015, as evidenced by the area of equivocal data in a horseshoe shape around the upstream end of that pier in the DoD map (fig. 54). However, on the downstream side of piers 7 and 8, substantial scour had occurred between 2015 and 2019 (fig. 54). The bedrock outcrops and stone revetment on the left (north) bank showed signs of localized scour and deposition throughout the reach between 2015 and 2019 (fig. 54), which was expected because of erroneous positioning during data collection in the 2015 survey (Huizinga, 2016) that created an offset of the data along the upstream left (north) bank between surveys.

The difference between the survey on August 14, 2019, and the previous flood survey on July 18, 2011 (fig. 55), indicates about 82 percent of the joint area of interest had detectable change, which means about 18 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation from 2015 to 2019 was moderate to substantial in the DoD map, deposition was predominant in the thalweg on the left (north) side and in the troughs of substantial dunes present in the 2011 survey (Huizinga, 2012), and scour was predominant throughout the middle and right (south) side of the reach (fig. 55). The average difference between the bathymetric surfaces was –2.28 ft (table 7), indicating moderate degradation between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 147,800 yd³, and the net volume of fill was about 49,900 yd³, resulting in a net loss of about 97,900 yd³ of sediment in the reach between 2011 and 2019. The cross sections from the two surveys along the upstream face of the bridge show the substantial difference in the surveyed sections (fig. 53). The frequency distribution of bed elevations in 2019 was remarkably similar to 2011 (fig. 52), but a slightly higher percentage of cells was at a lower channel-bed elevation than 2011 in the middle of the range (fig. 52). The scour hole near main channel pier 7 is shallower and narrower than in 2015, as indicated by the area of deposition in a horseshoe shape around that pier (fig. 55). The bedrock outcrops and stone revetment on the left (north) bank showed signs of localized deposition throughout the reach between 2011 and 2019 (fig. 55); however, the differences on the tops of the outcrops were within the uncertainties of the data, which implies there may be a slight horizontal offset to the 2019 data on the bank that is creating the appearance of deposition on the bank.

The difference between the survey on August 14, 2019, and the earliest nonflood survey on March 17, 2010 (fig. 56), indicates about 80 percent of the joint area of interest had detectable change, which means about 20 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation seemed nearly equal between scour and deposition from 2010 to 2019 in the DoD map, deposition was predominant along the thalweg on the left (north) side of the channel, and scour was predominant along the middle and right (south) side (fig. 56). However, the average difference between the bathymetric surfaces was –4.47 ft (table 7), indicating substantial channel degradation between the 2010 and 2019 surveys. The net volume of cut in the reach from 2010 to 2019 was about 192,700 yd³, and the net volume of fill was only about 13,700 yd³, resulting in a net loss of about 179,000 yd³ of sediment between 2010 and 2019. The cross sections from the two surveys along the upstream face of the bridge are similar to each other between the left (north) bank and pier 7 but are substantially different between pier 7 and the spur dike (fig. 53). The frequency distribution of bed elevations in 2019 seemed similar to 2010 but had a higher percentage of cells at lower channel-bed elevations than 2010 (fig. 52); however, the surveyed area was substantially wider in 2019 than in 2010 and extended higher on the channel banks, particularly on the right (south) side (fig. 56). The bedrock outcrops and stone revetment on the left (north) bank showed signs of minor, localized deposition and scour (fig. 56); however, much of the differences on the left (north) side of the channel—and particularly the tops of the outcrops—were again within the uncertainties of the data, as would be expected. As with previous DoD maps, substantial deposition or scour apparent at the faces of the pier footings results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The vertically averaged velocity vectors indicate mostly uniform flow throughout the reach, ranging from about 2 ft/s along the inside of the bend on the right (south) bank to 9 ft/s in the thalweg (fig. 57); however, turbulence and velocity reduction were observed downstream from the spur dike, debris raft, and pier 8, and moderate turbulence was observed in several transects (fig. 57).

The history of scour observed near pier 7 (Huizinga, 2010, 2012, 2016) led MoDOT to install scour countermeasures around pier 7 during August–October 2020. Partial surveys of the channel bed near pier 7 of structure A0767 were surveyed before and after installation of these scour countermeasures to document and verify installation. The historical scour hole near pier 7 was clearly evident in the pre-installation survey on August 17, 2020 (fig. 58), but the cofferdam for an expanded seal course had been partially installed, creating a partially widened footprint to the pier (fig. 58). The difference between the survey on August 13, 2019, and the partial survey on August 17, 2020, indicates moderate deposition of 3 to 7 ft had occurred in much of the partial reach from 2019 to 2020, but that scour of 15 to 20 ft had occurred near the pier (fig. 59). The cross sections from the two surveys along the upstream face of the bridge also indicates this deeper and wider scour hole at the pier in 2020 (fig. 53). The downstream and right (south) edges of the riprap blanket countermeasure installed around pier 7 was clearly evident in the post-installation survey on October 23, 2020 (figs. 60, 1.9B), and the difference between the pre- and post-installation surveys indicate the changes resulting from the installation (fig. 61). The net volume of cut in the partial reach from August 2019 to August 2020 was about 3,100 yd³, and the net volume of fill was about 14,300 yd³, resulting in a net gain of about 11,200 yd³ of sediment between August 2019 and August 2020 (fig. 59). The net volume of cut in the partial reach from August to October 2020 was about 5,300 yd³, and the net volume of fill was about 8,400 yd³, resulting in an additional net gain of about 3,100 yd³ of sediment between August and October 2020 (fig. 61). The scour hole was effectively mitigated because as much as 27 ft of deposition was near the pier (fig. 61), including some deposition of alluvial material on top of the blanket upstream from the bridge (fig. 60); nevertheless, moderate scour occurred in much of the partial reach around the riprap blanket between August and October (fig. 61).

Structures A4757 and L0568 (site 13; table 1) are dual bridges on State Highway 291, crossing the Missouri River at RM 352.7 on the northeastern side of the Kansas City, Mo., metropolitan area (fig. 1). The site was surveyed on August 14, 2019, and the average water-surface elevation of the river in the survey area, determined by the RTK GPS tide solution, was 720.1 ft (table 5; fig. 62). Streamflow on the Missouri River was about 141,000 ft³/s during the survey (table 5).

The survey area was about 1,640 ft long and averaged about 890 ft wide, extending from bank to bank in the main channel (fig. 62). The upstream end of the survey area was about 720 ft upstream from the centerline between structures A4757 and L0568 (fig. 42). The channel-bed elevations ranged from about 679 to 706 ft for most of the surveyed area (5th to 95th percentile range of the bathymetric data; table 5; fig. 63), except near the main channel piers of structures A4757 and L0568 (fig. 62). A channel thalweg was along the left (north) bank throughout the channel and was about 10 ft deeper than the middle of the channel (fig. 62). A row of medium dune features were observed in the thalweg on the left side of the channel, as well as numerous small dunes and ripples throughout the rest of the channel (fig. 62). As in previous surveys at this site (Huizinga, 2010, 2012, 2016), a noticeable channel constriction was at and immediately downstream from the bridges, and the left (north) bank was covered with stone revetment (fig. 62).

A large scour hole near the main channel piers (fig. 62) that essentially encompasses both piers had a minimum channel-bed elevation of about 664 ft (table 6), which also was the minimum channel-bed elevation for the entire reach (table 5). The main channel piers were skewed to the approaching flow, which caused a wide scour hole with somewhat unique characteristics as compared to scour holes at the other surveyed bridges. Pier 5 of structure L0568 was in the wake of pier 2C of structure A4757 and, therefore, had a poorly defined scour hole near it (fig. 62). At the upstream end of pier 2C of structure A4757, the minimum channel-bed elevation was about 664 ft, and at the upstream end of pier 5 of structure L0568, the minimum channel-bed elevation was about 672 ft (fig. 62; table 6). Information from bridge plans indicates that the main channel pier 2C of structure A4757 is founded on shafts drilled 20 ft into bedrock (fig. 64), and about 45 ft of bed material are between the bottom of the scour hole and bedrock at the point of minimum elevation of the scour hole near the upstream pier face (fig. 64; table 6). At the point of minimum elevation, the surveyed channel bed was about 2 ft below the bottom of the seal course elevation of 666.26 ft (table 6). Information from bridge plans indicate that the main channel pier 5 of structure L0568 is a caisson on bedrock (fig. 65), and about 47 ft of bed material are between the bottom of the scour hole and bedrock at the point of minimum elevation of the scour hole near the downstream right (south) corner (fig. 65; table 6).

The difference between the survey on August 14, 2019, and the previous nonflood survey on June 4, 2015 (fig. 66), indicates about 74 percent of the joint area of interest had detectable change, which means about 26 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Bed variation seemed nearly equal between scour and deposition from 2015 to 2019 in the DoD map, deposition was predominant from the upstream left through the downstream right of the reach, and scour was predominant from the upstream right to the downstream left (fig. 66). The average difference between the bathymetric surfaces was –1.51 ft (table 7), indicating minor to moderate degradation between the 2015 and 2019 surveys. The net volume of cut in the reach from 2015 to 2019 was about 82,100 yd³, and the net volume of fill was about 25,100 yd³, resulting in a net loss of about 57,000 yd³ of sediment between 2015 and 2019. The cross sections from the two surveys along the upstream face of the upstream bridge are similar to each other but generally with uniform scour of 5 to 10 ft across the section (fig. 64). The cross sections from the two surveys along the upstream face of the downstream bridge also are similar to each other but generally with uniform scour of 10 ft across the section (fig. 65). The frequency distribution of bed elevations in 2019 was very similar to 2015, but a higher percentage of cells were at slightly lower channel-bed elevations in 2019 (fig. 63). The scour hole near upstream pier 2C was similar to 2015, as evidenced by the area of equivocal data in a horseshoe shape around the upstream end of that pier in the DoD map (fig. 66). However, the scour hole was slightly deeper near downstream pier 5 than in 2015, as evidenced by the area of scour starting at the downstream side of upstream pier 2C and extending downstream around pier 5 in the DoD map (fig. 66). The stone revetment on the left (north) bank showed signs of nearly uniform deposition throughout the reach between 2015 and 2019, which is somewhat unexpected (fig. 66); as indicated with others surveys in the current study, there may be a horizontal offset to the 2019 data on the bank that is creating the appearance of deposition. The potential for a horizontal offset is substantiated by the appearance of substantial scour on the left (north) faces and deposition on the right (south) faces of the footing and caisson that likely results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 14, 2019, and the previous flood survey on July 19, 2011 (fig. 67), indicates about 85 percent of the joint area of interest had detectable change, which means about 15 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial but approximately balanced bed variation was apparent from 2011 to 2019 in the DoD map, substantial scour was throughout the upstream part and along the right side of the reach, and substantial deposition was along the thalweg along the left (north) side and in the troughs of substantial dunes present in the 2011 survey (Huizinga, 2012, fig. 67). The average difference between the bathymetric surfaces was +0.22 ft (table 7), indicating little net different between the 2011 and 2019 surveys. The net volume of cut in the reach from 2011 to 2019 was about 77,900 yd³, and the net volume of fill was about 87,400 yd³, resulting in a net gain of about 9,500 yd³ of sediment in the reach between 2011 and 2019. However, the cross sections from the two surveys along the upstream faces of the bridges show the substantial difference in the surveyed sections (figs. 64, 65). The frequency distribution of bed elevations in 2019 also was substantially narrower than 2011 because a higher percentage of cells was at the middle range of elevations (fig. 63). The DoD map shows that the substantial scour hole at upstream pier 2C was smaller and shallower in 2019, as evidenced by the horseshoe-shaped deposition around the nose of the pier (fig. 67). As with the DoD map for 2015 to 2019 (fig. 66), the stone revetment on the left (north) bank showed signs of localized deposition throughout the reach between 2011 and 2019, which is somewhat unexpected (fig. 67); however, the differences on the tops of steps in the bank were within the uncertainties of the data, which implies there may be a horizontal offset to the 2019 data on the bank that is creating the appearance of deposition. The appearance of substantial scour on the left (north) faces and deposition on the right (south) faces of the footing and caisson also likely results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The difference between the survey on August 14, 2019, and the earliest nonflood survey on March 18, 2010 (fig. 68), indicates about 75 percent of the joint area of interest had detectable change, which means about 25 percent of the differences in the joint area of interest are equivocal and within the uncertainty. Substantial but approximately balanced bed variation was apparent from 2010 to 2019 in the DoD map, scour was predominant in the upstream area and along the right (south) bank downstream, and deposition was in the substantial scour hole near the piers and troughs of large dunes in the downstream channel present in the 2010 survey (Huizinga, 2010; fig. 68). The average difference between the bathymetric surfaces was –2.82 ft (table 7), indicating moderate channel degradation between the 2010 and 2019 surveys. The net volume of cut in the reach from 2010 to 2019 was about 127,200 yd³, and the net volume of fill was about 24,600 yd³, resulting in a net loss of about 102,600 yd³ of sediment between 2010 and 2019. The cross sections from the two surveys along the upstream face of the bridge are similar to each other, except near the piers and between the piers and the right (south) banks (figs. 64, 65). The frequency distribution of bed elevations in 2019 was similar to 2010 at lower elevations but became different with increasing elevation, and a lower percentage of cells was at higher channel-bed elevations (fig. 63); however, the surveyed area was substantially wider in 2019 than in 2010 and extended higher on the channel banks, particularly on the right (south) side (fig. 68). The stone revetment on the left (north) bank showed signs of minor, localized scour and deposition, and much of the difference was within the uncertainties of the data, as would be expected. As with previous DoD maps, and substantial deposition or scour apparent at the faces of the pier footing results from minor horizontal positional variances between the surveys (see “Uncertainty Estimation” section).

The vertically averaged velocity vectors indicate mostly uniform flow throughout the reach, ranging from about 2 ft/s along the inside of the bend on the right (south) bank to about 9 ft/s in the thalweg (fig. 69). Exceptions to uniform flow include flows angled to the left (north) near the upstream and downstream faces of the bridges (fig. 69). Moderate turbulence also was observed in several transects, particularly near the bank protrusions near the bridges and downstream from the main channel piers (fig. 69). Velocities were slightly lower downstream from the bridges, likely caused by the flow expansion downstream from the constriction at the bridges (fig. 69).

Several of the findings at each surveyed bridge were common to all the bridges, and some findings were evident only when results of the surveys were examined as a set. These general findings are of benefit in the assessment of scour at the surveyed bridges, as well as other bridges close by or in similar settings.