31 Aug 2022

Sediment Supply from Bank Caving on the Lower Mississippi River, 1765 to Present

Abstract: Bank caving rates and associated total sediment supply were calculated along the Lower Mississippi River from Cairo, IL, to Baton Rouge, LA, using historical maps between 1765 and 1992. Comparison of these maps reveals that the added sediment loads from bank erosion have greatly declined through time. In the pre-1960s period, erosion rates generally ranged from approximately 300 million cubic yards (MCY) to 400 MCY, with the 1880–1930s period having the highest erosion rates of approximately 600 MCY. By the 1990s, the sediment supply from bank erosion was essentially eliminated, with significant erosion being observed at only a few locations, totaling approximately 40 MCY/year. This equates to approximately a 90% reduction in the amount of total sediment being supplied to the channel system from bank erosion.

19 Aug 2022

The Old River, Mississippi River, Atchafalaya River, and Red River (OMAR) Technical Assessment

NOTE: The Old River, Mississippi River, Atchafalaya River, and Red River (OMAR) Technical Assessment is a 9-volume series of reports that was produced under the direction of the Mississippi River Geomorphology & Potamology Program. An abstract from the main report, Volume 1, is listed below, along with the individual volume titles and links to the relevant reports. ABSTRACT: This is the main report of Old River, Mississippi River, Atchafalaya River, and Red River (OMAR) Technical Assessment. The primary objective of the OMAR Technical Assessment was to conduct a comprehensive evaluation that aimed to understand the impacts of former and potential changes to the system in the vicinity of the Old River Control Complex (ORCC) over time, the water and sediment delivery regime at the ORCC, and the effects to the river system surrounding the ORCC. Scenarios evaluated in this technical assessment were designed to investigate potential system responses to a wide range of possible operational alternatives and identify knowledge gaps in current understanding of system behavior. This report summarizes and synthesizes the individual reports detailing the investigations into specific aspects of the ORCC and the surrounding region.

20 May 2022

Low-Sill Control Structure Gate Load Study

Abstract: The effort performed here describes the process to determine the gate lifting loads at the Low-Sill Control Structure. To measure the gate loads, a 1:55 Froude-scaled model of the Low-Sill Control Structure was tested. Load cells were placed on 3 of the 11 gates. Tests evaluated the gate loads for various hydraulic heads across the structure. A total of 109 tests were conducted for 14 flows with each flow having two gate settings provided by the United States Army Corps of Engineers, New Orleans District. The load data illustrated the potential for higher gate lifting loads (GLL) to occur at the mid-range gate opening (Go) for Gates 3 and 6. While for Gate 10, the highest GLL (452 kips, maximum load in testing) was at a Go = 4.2 ft. Conversely, for the low-flow bays, the highest load occurred at Go = 24.86 ft.

5 May 2022

Waterborne Geophysical Investigation to Assess Condition of Grouted Foundation: Old River Control Complex – Low Sill Structure, Concordia Parish, Louisiana

Abstract: The Old River Low Sill Structure (ORLSS) at the Old River Control Complex (ORCC) in Concordia Parish, LA, is a steel pile-founded, gated reinforced-concrete structure that regulates the flow of water into the Atchafalaya River to prevent an avulsion between the Mississippi River and the Atchafalaya River. A scour hole that formed on the southeast wall of ORLSS during the Mississippi River flood of 1973 was remediated with riprap placement and varied mixtures of self-leveling, highly pumpable grout. Non-invasive waterborne geophysical surveys were used to evaluate the distribution and condition of the grout within the remediated scour area. Highly conductive areas were identified from the surveys that were interpreted to consist mostly of grout. Resistive responses, likely representing mostly riprap and/or sediment, were encountered near the remediated scour area periphery. A complex mixture of materials in the remediated scour area is interpreted by the more gradual transitions in the geophysical response. Survey measurements immediately beneath ORLSS were impeded by the abundance of steel along with the structure itself. The survey results and interpretation provide a better understanding of the subsurface properties of ORLSS.

9 Sep 2021

Geophysical Investigation to Assess Condition of Grouted Scour Hole: Old River Control Complex—Low Sill Concordia Parish, Louisiana

Abstract: Geophysical surveys, both land-based and water-borne, were conducted at the Old River Control Complex‒Low Sill, Concordia Parish, LA. The purpose of the surveys was to assess the condition of the grout within the scour region resulting from the 1973 flood event, including identification of potential voids within the grout. Information from the ground studies will also be used for calibration of subsequent marine geophysical data and used in stability analysis studies. The water-borne survey consisted of towed low frequency (16-80 MHz) ground penetrating radar (GPR), whereas the land-based surveys used electrical resistivity and seismic refraction. The GPR survey was conducted in the Old River Channel on the upstream side of the Low Sill structure. The high electrical conductivity of the water (~50 mS/m) precluded penetration of the GPR signal; thus, no useful data were obtained. The land-based surveys were performed on both northeast and southeast sides of the Low Sill structure. Both resistivity and seismic surveys identify a layered subsurface stratigraphy that corresponds, in general, with available borehole data and constructed geologic profiles. In addition, an anomalous area on the southeast side was identified that warrants future investigation and monitoring.

7 Sep 2021

A Bathymetric Study of the Forebay at the Old River Low Sill Structure from 1963 to 2019

Purpose: The purpose of this study is to use historical hydrographic surveys to quantify bathymetric changes in the forebay channel area of ORLSS over the last 56 yr. The results from this comparison support an ongoing geotechnical study led by Mr. Lucas Walshire, U.S. Engineer Research and Development Center (ERDC), for the U.S. Army Corps of Engineers, New Orleans District (USACE MVN).

12 May 2021

Automated Characterization of Ridge-Swale Patterns Along the Mississippi River

Abstract: The orientation of constructed levee embankments relative to alluvial swales is a useful measure for identifying regions susceptible to backward erosion piping (BEP). This research was conducted to create an automated, efficient process to classify patterns and orientations of swales within the Lower Mississippi Valley (LMV) to support levee risk assessments. Two machine learning algorithms are used to train the classification models: a convolutional neural network and a U-net. The resulting workflow can identify linear topographic features but is unable to reliably differentiate swales from other features, such as the levee structure and riverbanks. Further tuning of training data or manual identification of regions of interest could yield significantly better results. The workflow also provides an orientation to each linear feature to support subsequent analyses of position relative to levee alignments. While the individual models fall short of immediate applicability, the procedure provides a feasible, automated scheme to assist in swale classification and characterization within mature alluvial valley systems similar to LMV.

30 Apr 2021

Empirical analysis of effects of dike systems on channel morphology of the Lower Mississippi River

NOTE: There was an title error in MRG&P Report No. 36, which was published 3/2/2021 . A new PDF has been attached to the record with the correct title. This email has the correct title as well. No other changes were made.

29 Jan 2021

Mississippi River Adaptive Hydraulics Model Development and Evaluation, Commerce to New Madrid, Missouri, Reach

Abstract: A numerical, two-dimensional hydrodynamic model of the Mississippi River, from Thebes, IL, to Tiptonville, TN (128 miles/206 km), was developed using the Adaptive Hydraulics model. The study objective assessed current patterns and flow distributions and their possible impacts on navigation due to Birds Point New Madrid Floodway (BPNMF) operations and the Len Small (LS) levee break. The model was calibrated to stage, discharge, and velocity data for the 2011, 2015–2016, and 2017 floods. The calibrated model was used to run four scenarios, with the BPNMF and the LS breach alternately active/open and inactive/closed. Effects from the LS breach being open are increased river velocities upstream of the breach, decreased velocities from the breach to Thompson Landing, no effects on velocity below the confluence, and cross-current velocities greater than 3.28 ft/s (1.0 m/s) within 1186.8 ft (60 m) of the bankline revetment. Effects from BPNMF operation are increased river velocities above the confluence, decreased velocities from the BPNMF upper inflow crevasse (Upper Fuseplug) to New Madrid, cross-current velocities greater than 1.5 ft/s (0.5 m/s) only near the right bank where flow re-enters the river from the BPNMF lower inflow/outflow crevasse Number 2 (Lower Fuseplug) and St. Johns Bayou.

1 Dec 2020

Seamless Digital Elevation Model (DEM) Creation for the Mississippi River in Louisiana to Support Hydrologic Modeling

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