Posted on July 13, 2022
RANKIN CO., Miss. (WLBT) – Over the next year, enough dirt will be removed from the bottom of the Barnett Reservoir to fill more than 27.5 Olympic-size swimming pools.
Crews are currently dredging portions of the lake as part of ongoing maintenance to keep boat channels open and maintain water levels.
In all, about 90,000 cubic yards of sediment will be removed. That amount is equivalent to nearly 18.2 million gallons. By comparison, an Olympic-sized pool holds around 660,000 gallons of water.
Work began in May and will continue into April of next year, said Mark Beyea, chief engineer with the Pearl River Valley Water Supply District.
The district maintains the reservoir and surrounding properties and is responsible for bringing on contractors to survey the lake and remove sediment as needed.
“It’s needed because the lake can only go so high. The water has to stay at certain levels, so we don’t get in danger of overtopping the dam,” he said.
Beyea said the dredging also is necessary to keep the boat channels open, ensuring that recreation along the lake can continue.
“If you didn’t dredge the water would get so shallow, boats would hang up in the shallow spots,” he said. “If you let sediment build up, you would reduce the water available to supply Jackson as well.”
The reservoir includes a 24,000-acre open-water lake and 9,000 acres of “riverine habitat” that serves as a water supply for the Capital City, as well as a recreational area for the state.
The lake, on average, is about 10 feet deep, but reaches depths of more than 70 feet in some spots, Beyea said.
Water in the reservoir is supplied by the Pearl River and other tributaries.
“You have the creeks and river that come into the lake and bring with them sand, silt, and other soils,” he explained. “It gets into the pool here, and it comes to a stop, basically. The sand will drop out, because it’s heavier, followed by other soil particles.”
“They’re effectively filling the lake over time. If we didn’t take some of that out, it would eventually fill back in and become a river channel.”
Beyea says it takes several years to plan a dredging project, with a contractor coming in to conduct a survey of the lake bottom.
“They come in with a boat and sonar-type equipment and map the bottom of the lake. We had all of Pelahatchie Bay, [and] some of the smaller areas of the main lake mapped in 2020. The consultant that did that identified the boat channels with the shallowest water and gave us a priority list of channels that needed to be dredged.”
Materials are broken up by a large cutter and then are essentially vacuumed up by a 10-inch hose.
Work is being done by Hemphill Engineering and M&N of Alabama, LLC, a subcontractor. In all, the dredging is expected to cost around $2.7 million and is being funded with state allocations and revenues PRV generated from selling timber on reservoir land.
The project likely should not impact boating and fishing on the reservoir. Orange markers are being placed to mark where floating and submerged pipelines are located.
Once collected, the sediment is placed in a special retaining pond away from the main body of water, where it will be dried out, vegetated, and returned to a natural state.
Environmental regulations do not allow the sediment to be placed back into the body of water it is taken from. It also can no longer be placed directly onto a shore of that body of water, Beyea said.
“A lot of islands in the lake are from dredge materials from years past,” Beyea said. “The beach at Pelahatchie Shore was made from dredged material.”
