Bed topography for the Mississippi River at Vicksburg, Mississippi, for selected flows 2011-2016

Authors: Wren, Daniel; MCALPIN, TATE - Us Army Corp Of Engineers (USACE); Smith Iv, James; JONES, KEATON - Us Army Corp Of Engineers (USACE); Kuhnle, Roger; ABRAHAM, DAVID - Us Army Corp Of Engineers (USACE)

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2022
Publication Date: 11/24/2022
Citation: Wren, D.G., Mcalpin, T.O., Smith Iv, J.E., Jones, K.E., Kuhnle, R.A., Abraham, D.A. 2022. Bed topography for the Mississippi River at Vicksburg, Mississippi, for selected flows 2011-2016. Journal of Hydraulic Engineering. 149(2):04022039-1:04022039-12 https://ascelibrary.org/doi/10.1061/JHEND8.HYENG-13295.

Interpretive Summary: The bottom of large rivers like the Mississippi are often made of sand that, under the influence of flowing water, becomes organized in to shapes called bedforms. The size and shape of the bedforms affect the the depth of flood flows, which is important information for forecasting the impact and extent of flooding. In addition, measurements of the bedforms can yield estimates of the amount of sand moving down rivers. This information is needed for assessing the impact of engineering measures and for other river management decisions such as ecological habitat maintenance in coastal marsh areas. In this study, acoustic measurements of the bottom topography of the Mississippi River during several periods, including the flood of 2011, are analyzed to see how the sand bedforms changed in response to the flows. The data were collected near Vicksburg, Mississippi over a river section that approximately one kilometer long. We found that existing relationships for predicting bedform size could be used if they were altered slightly to find the conditions in the Mississippi River. The size and shape of the bedforms depended on how close the measurement was to peak flow rates during flood events. The size and shape of bedforms also depended on how far from the river bank the measurement was taken. These results can be used by river engineers, particularly those responsible for decisions about the Mississippi River, to better understand how large flow rates influence the characteristics of sand bedforms at the bottom of the river.

Technical Abstract: Quantification of sediment transport rates and total mass flux over longer timescales is necessary for river management but remains difficult to measure in the field due to large volumes of sediment in motion, spatiotemporal heterogeneity in river conditions such as discharge, depth, and morphology, the need for expensive equipment, and personnel costs. Repeated surveys of bottom topography, collected at different times for the same reach, can be used to provide bedload transport measurements in rivers. The U.S. Army Corps of Engineers-Engineer Research and Development Center (USACE-ERDC) collected acoustic multi-beam topographic surveys in the Mississippi River near Vicksburg, MS, USA, to measure sediment bedload during the unusually high flows that occurred during May and June of 2011. In addition, topography data from three other dates are included for comparison. Here, the bottom topography data have been analyzed to quantify aspects of bed topography and trends caused by changing flows during this extreme event. Data from lower, more typical flows are also included to illustrate the differences caused by the flood flows. Bedform dimensions were strongly affected by position in the channel cross-section, with lower amplitude, shorter length bedforms near the east bank, larger bedforms near the west bank, and much higher and longer bedforms in the center section of the channel. Superimposed bedforms were found for flows on the falling limb of the 2011 flood hydrograph. Bedform amplitudes and lengths were positively correlated with flow depths, but the bedform amplitudes were typically higher and lengths were shorter than those predicted by Bradley and Venditti (2017), with the exception of bedforms near the east bank. Best fit power law relationships are given for bedform amplitude and length. In addition, topography data from lower, more typical flows are included for comparison, and to illustrate the morphometric variation induced by a wide range of discharges.