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).