12 Mar 2025

Old River Control Low Sill Structure: Monitoring and Performance

Abstract: The Old River Low Sill Structure (ORLSS) is located approximately 25 mi south of Vidalia, LA, and is part of the Old River Control Complex. The structure is founded on steel piles and is a 566-foot-long concrete structure constructed in 1959. The structure resembles a dam with 11, 44-foot-wide gates to prevent migration of the Mississippi River’s current course to a hydraulically shorter course down the Atchafalaya River. A re-analysis was undertaken by the US Army Engineer Research and Development Center to investigate the current level of stability and the potential for adjusting the operating limitations placed on the structure because of damage during the 1973 flood. The investigation was performed by reviewing the design and post-design stability analyses, analyzing performance data, and performing an updated stability analysis. The stability analysis was performed with monitoring data that spanned several decades. Using historic monitoring data in the stability analysis, with a wide range of loading conditions, it was shown that uplift conditions were not as severe as previously considered. Performance data coupled with the stability analysis show that the structural performance supports the current operating conditions.

3 Mar 2025

Low-Sill Control Structure: Physical Modeling Investigation—Potential Upstream Dike Fields

Abstract: The model investigation reported herein describes the process to analyze the effects of proposed dikes in various locations upstream of the Low-Sill Control Structure (LSCS) using an existing 1:55 Froude-scaled physical model. The purpose of this effort was to utilize the physical model to explore potential configurations of river-training structures in the approach channel that would result in more uniform flow conditions at the structure. This analysis was conducted by constructing dikes out of both sandbags and rock. Each dike configuration was surveyed using lidar and then tested by collecting particle-tracking velocimetry data. A total of nine dike configurations were tested in the physical model, and the resulting flow fields in the approach channel were provided to the US Army Corps of Engineers, Mississippi Valley Division. Most configurations resulted in data that showed improved, straighter flow paths in the approach channel. The results of these tests indicated that an L-head dike configured as the 50 ft stone dike 1-23A provided relatively straight flow conditions approaching the LSCS with relative uniform velocities across the channel.

21 May 2024

Low Sill Control Structure: Physical Modeling Investigation of Riprap Stability Downstream of End Sill

The model investigation reported herein describes the process to model and analyze the stability of scaled riprap in the existing 1:55 Froude-scaled Low Sill Control Structure physical model. The existing model is a fixed-bed model, so modifications were made to create a testing section for the scaled stone. Three separate gradations of scaled riprap were tested at varying boundary conditions (discharge, head and tailwater elevations, and gate openings). Each test was surveyed using lidar for pre to posttest comparisons. It was found that Gradation B remained stable throughout the tests in the physical model.

14 May 2024

Low Sill Control Structure: Physical Modeling Investigation of Velocities Downstream of the End Sill

Abstract: The model investigation reported herein describes the process to measure velocities at various locations downstream of the Low Sill Control Structure using an existing 1:55 Froude-scaled physical model. To collect these measurements, an acoustic-Doppler velocimeter was deployed downstream of the structure at varying locations and depths. A total of 79 velocity measurements were taken across nine flow conditions (discharge, head and tailwater elevations, and gate openings) provided by the US Army Corps of Engineers, New Orleans District.

20 Mar 2023

Old River Control Complex (ORCC) Low Sill: A Literature Synthesis

Abstract: The US Army Corps of Engineers (USACE), New Orleans District (MVN), tasked the US Army Engineer and Research Development Center (ERDC) with assessing the condition of a grouted scour hole located at the southeast wall of the Old River Low Sill Structure (ORLSS) at the Old River Control Complex (ORCC) using noninvasive techniques, such as geophysical surveys and physical models. This special report (SR) combines a scientific literature synthesis of previous research with further geologic interpretation as a first step in the overall task assigned by MVN. The results discussed in this SR will be used to inform the interpretation of geophysical surveys, construction of physical models, and input for the slope stability analyses.

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).