What comes to mind when you hear the term physical model? Do you think of it as something you can touch and feel? Do you picture something from your childhood such as a model airplane or car? Or do you think of it as a miniature replica of a building or design project?

The U.S. Army Corps of Engineers (USACE) Vicksburg District, in coordination with the U.S. Army Engineer Research and Development Center (ERDC) has recently developed a physical model of the Yazoo Backwater Pump project.

Vicksburg District senior project manager Kristen Camp said, “This model was required to accurately answer some of the questions and challenges needed during the design and plan development. It can also be used after the pump station is constructed to address potential hydraulic- and engineer-related issues.”

The 1:17.62 scale model was completed in March 2022 and consists of all the relevant hydraulic components required to investigate the approach flow entering the pump station, including an approach channel, wingwalls, intake bays, formed suction intakes and pump columns. The model is used to reflect the intake condition of the flow that’s approaching from the inlet channel. There are a lot of different things that could impact the intake conditions, such as how much riprap is in the water, how the inlet channel is designed, how wing walls are angled, the width of bays, etc.

ERDC’s Coastal & Hydraulics Laboratory is assisting the Vicksburg District in the evaluation of the hydraulic performance of the intakes of the pumps for the proposed Yazoo Backwater Pumping Plant. According to the Hydraulic Institute Standards, there’s certain criteria these pumps have to meet to perform adequately.

Kiara Pazan, research civil engineer and project lead, explained a few of the testing methods used to identify existing hydraulic conditions such as figuring out the severity and frequency of vortices in the intake, detecting the intensity of the rotation of flow in the suction column, and determining the velocity uniformity in the suction column.

“We want to make sure that if there is any adverse hydraulic condition that could affect performance, we are able to identify it now,” Pazan said.

One aspect in which testing has proved beneficial is identifying unacceptable vortices in the intake which were not anticipated. Pazan and her team will finish testing within the next couple of weeks and will provide data results to the Vicksburg District with recommendations on how to remediate potential issues.

The Yazoo Backwater area project is located in the lower portion of the Yazoo River within the state of Mississippi. In nine of the last 11 years, the Yazoo Backwater Area has experienced significant flooding. This flooding primarily occurs in the spring when the two outlets, Steele Bayou and Little Sunflower structures, which control the 4,093 square mile drainage area, are closed due to high Mississippi River stages. The Yazoo Backwater area is protected by levees on all sides. When the structures are closed, rainfall within the basin becomes trapped and rises until the Mississippi River stages recede sufficiently to allow these structures to be once again opened.

The Vicksburg District has designed an updated pump station for the Yazoo Backwater area to release the accumulated rainfall during the high flood events. The proposed pump system consists of 12 vertical pumps for a total volume to be pumped of 14,000 cfs. The pumping plant would reduce flood stages on lands and infrastructure in the project area. However, the pump would not be operated until stages inside the levees reached an elevation of 87 feet at which point over 135,000 acres of primarily forested wetlands would be inundated. Also, any time the stages of the Mississippi River are lower than the interior stages, the pump station would be cutoff, and the gated structures opened to allow gravity evacuation of the flood waters.

In 2019, the Yazoo Backwater area experienced the greatest flood since 1973. Approximately 430,000 acres were inundated with floodwater damaging homes, roads, farms, businesses, churches, wildlife management areas, agricultural land, and forested areas for over six months. Additionally, two deaths were attributed to the flooding. The Yazoo Backwater area received attention from Congressional members, and interagency meetings were held once again. The EPA directed the Vicksburg District to provide updated changes and revisions to the previous report that was completed in 2008. The updated report was completed and released in December 2019, but no comments were received from the EPA.

In 2020, the Yazoo Backwater area once again experienced significant flooding inundating over 370,000 acres. On November 30, 2020, the EPA formally stated full support of the project to reduce flood damages and that the proposed project was not subject to EPA’s 2008 Final Determination veto.

Congress provided funding to initiate design of an updated pump project in March 2021. Numerous visits to the Yazoo Backwater area occurred over the summer and fall of 2021 by the office of the Assistant Secretary for the Army for Civil Works (ASA(CW) to meet with Congressionals, Mississippi Valley Division and Vicksburg District senior leaders, environmental agencies and concerned citizens. EPA Administrator Michael Regan and EPA Assistant Administrator for Water Ms. Radhika Fox also traveled to Vicksburg, Miss. However, later that month, the EPA wrote the ASA(CW) stating the 2020 plan for the Yazoo Pump Project was prohibited by the 2008 Final Determination.

The project was presented to the Council on Environmental Quality (CEQ) at the beginning of 2022, and the Vicksburg District continues to support requests for information from the ASA(CW) office in support of CEQ’s interagency discussions with EPA and FWS to determine a path forward for this project.

The Yazoo Backwater Project was authorized by the 1941 Flood Control Act as part of the Mississippi River and Tributaries System (MR&T). The MR&T protects people, infrastructure, commerce, agriculture, and energy. $1.75 trillion in flood damages have been prevented along the Mississippi River.

The Yazoo Backwater project has four major features: The Yazoo Backwater area levee, connecting channel, associated water control structures and the Yazoo Backwater area pumping station. All but the pumping station were completed by 1978. Construction of the pumping station is the last remaining piece of the puzzle.