Posted on July 31, 2023
A dredging company has completed construction of an underwater sill across the bottom of the Mississippi River at Myrtle Grove to block saltwater from the Gulf of Mexico from reaching public and industrial water supplies in upper Plaquemines and St. Bernard parishes as well as New Orleans.
New Jersey-based Weeks Marine Inc. began dredging from a borrow area on the right descending side of the river just upstream on July 11 and 12, using its J.S. Chatry cutterhead dredge and a fleet of smaller boats to keep a surface and underwater pipeline in place to dispose of the sediment on the river bottom. Construction was completed on Wednesday.
The Defense Department awarded Weeks Marine’s Covington office an $8.9 million addition to an existing river dredging contract to pay for the dam.
A pipeline extends into the middle of the Mississippi River to deliver sediment for a dam being built at the river’s bottom to block saltwater moving upriver from the Gulf of Mexico.
The river is about 90 feet deep at that location, and the sill was built so its top is 55 feet below the surface, which allows ocean-going vessels to move upriver.
The U.S. Coast Guard required vessels to follow one-way traffic rules along about two miles of the river where the dredging operation was taking place.
The sill is at mile marker 63.7 above Head of Passes, and the most recent survey of the leading toe of saltwater found it had retreated to about mile marker 52 because of upriver rainfall during the past three weeks.
Another view of the J.S. Chatry dredge as it collects sediment from a borrow area to build an underwater dam in the river.
However, the National Weather Service’s Lower Mississippi River Forecast Center is predicting that water levels in the lower stretch of the river will resume falling over the next 28 days. On Friday, the water level at the Carrollton Gauge in New Orleans was at 3.1 feet, and it was expected to drop to 1.8 feet by Aug. 24.
Saltwater continues to contaminate the water intake for Plaquemines Parish’s Boothville water treatment plant, which supplies residents on the west bank from Empire Bridge to the Venice area.
The parish is distributing bottled water and ice to residents between 8 a.m. and 1 p.m., Monday through Friday, at the Buras and Boothville-Venice fire stations.
Floats keep a pipeline elevated as it delivers sediment for construction of an underwater sill.
Construction of a booster pump to allow water from the Belle Chasse water plant to reach Venice has been delayed until the week of Aug. 14 because of manufacturing and parts shortages, said Shannta Carter, a spokesperson for the parish.
Repair work at the parish’s Port Sulphur water treatment plant is not yet completed. The parish also continues to work with the Corps to obtain reverse osmosis equipment that would remove saltwater at the Boothville and East Pointe a la Hache water plants, she said.
The underwater dam is designed to block saltwater from reaching the water intakes for the parish’s Belle Chasse and Dalcour plants, as well as the intakes for industries and other communities upriver.
When higher water levels result in increased rates of flow in the river later this year, that will push saltwater back towards the Gulf. The faster water flow also will erode the underwater sill.
The low, slow river water levels have not yet caused shoaling issues in the lower river that could affect ocean-going vessels, but the Corps plans to assign a cutterhead dredge to work in Southwest Pass to maintain its 50-foot-deep channel later this year, said spokesperson Ricky Boyett.
