Mississippi River at decade low, affecting shipping and drinking water | environment

The Mississippi River is at its lowest level in a decade, with levels on the Carrollton Scale in New Orleans only 3 feet above sea level, and the Great River’s weak flow is wreaking havoc on shipping as well as the drinking water supply below the city.

The river is so low that Army Corps of Engineers officials last week announced a plan to build a 45-foot-high wall across the river bed to prevent a “wedge” of salt water from moving upstream toward the water intakes. The Corps had to take similar action in 2012 – the last time the water was very low – as well as in 1999 and 1988.

During times of high water, usually in the spring, the river surface is much higher. The Corps initiates “anti-flooding” protocols when the surface is 11 feet above sea level; In 2020, the river has been at this level or higher for six months. Flood walls and dams protect New Orleans to at least 22 feet above sea level.

In Lower Plaquemines Parish, where a salt wedge is already affecting drinking water, Hurricane Ian has derailed an effort to desalinate river water. A parish official said Tuesday that a reverse osmosis unit that the parish was trying to lease for a drinking water treatment plant in Boothville on the east bank of the river was delayed at least a week after the unit was redirected to a Florida water plant hit by Ian. .

“That first unit was deployed in Florida, so a unit in Texas is now being refurbished with new membranes, and we hope to have it installed no later than next week,” said Patrick Harvey, director of the Home Diocese Office. Prepare for security and emergency preparedness.

He said the unit could already be installed as early as Friday, if all goes well. Entergy is already installing a new electrical pole and wiring at its Boothville facility to energize the unit.

He said a second unit is expected to be deployed at the Pointe water treatment plant in La Hache on the West Bank within a few weeks.

A drinking water warning remains in effect for residents who use water from the Boothville facility from Empire Bridge to Venice due to the high levels of sodium and chlorate in the water.

Salt water heads upriver from the Gulf of Mexico due to less rainfall this spring, summer, and fall in the Mississippi, Ohio, and Missouri River valleys. The low flow of the Mississippi allows salt water to slowly infiltrate northward under the river’s fresh water.

Carrollton measured water levels in New Orleans

This graph tracks the water level on the Carrollton Scale, in the river at the Army Corps of Engineers headquarters building in New Orleans, from January 1 to October 4, 2022. The record drop at this location, the red line, minus 1.6 feet, was on December 27, 1872. The blue line designates the water level of 11 feet, which is considered “the bank is full” at this scale.

The main “toe” of this wedge was at mile 47.9 on Tuesday, just below the water inlet Pointe a La Hache, and it had slowed in its movement north, according to Ricky Boyet, a spokesman for the Legion’s New Orleans County Sheriff’s Office. .

But he said he had not slowed enough to cancel the Corps’ plan to build a 1,500-foot-wide “threshold” across the river bed near the Phillips 66 Alliance refinery. The sill would prevent the salt water from moving north enough to affect the two larger Plaquemines water treatment plants, Belle Chasse and Dalcour.

The dam would also prevent salt water from moving away from the river, where it could threaten industrial water intakes and water intakes in New Orleans.

Effects on charging

The US Coast Guard also warned shippers of the potential dangers from low waters. An advisory report issued on September 23 warned merchant ships to be wary of shoals – sediment growth in shipping channels – as far north as 167.5 miles above the head of the fairways, in St James Parish.

The Coast Guard announced Tuesday that it has responded to eight land barges from the river over the past week due to low water levels, including near Stack Island, Mississippi, and in Memphis, where waterways restrictions have been imposed.

In the New Orleans area, the proposed threshold is expected to become an obstacle to oceangoing vessels using the canal, as ships will only be allowed to cross a draft of 45 feet, rather than the 50-foot draft. After the river has recently deepened from New Orleans to the mouth of the river.

This will require ships to be loaded with less tonnage or cargo to be transferred to other ships or barges south of the bulkhead.

North Louisiana, similar shoals have forced barges to allow smaller quantities of cargo, including soybeans that would normally be taken to ocean-going ships in Louisiana for shipment overseas, said Mike Steinhoek, executive director of the Soybean Transportation Coalition.

He said the narrow waterways in the upper basin also reduced the number of barges that were tied together.

“Barge fleets usually have 35 to 40 boats held together,” he said. “Now the maximum allowed is only 25 due to the width of the channel.”

The result, he said, is a double whammy that affects both upstream grain elevators and soybean growers. He said there was a 41% increase in barge freight rates this year compared to last year, and some farmers were turned away by lifts because the lack of barges meant the lifts were kept full for longer.

The lower depths in parts of the river system have resulted in the need for individual barges to carry a foot or two less soybeans. That could reduce cargo tonnage by about 10%, Steinhoek said.

A slight rise is expected

There will likely be a slight increase in river flow next week, in part because up to 3 inches of rain fell into the Ohio River Basin over the weekend as a result of Hurricane Ian, said Jeffrey Graschel, a hydrologist at the River Forecast Center. Lower Mississippi National Weather Service, based in Slidell.

River level forecast for New Orleans

These two graphs show the official forecast, higher, of water levels on the New Orleans Carrollton Scale for 28 days, based on the past two days and two estimated days of future precipitation; And an empirical forecast, below, based on plast and 16 days of precipitation in the future. Both conclude that the river will remain low through the rest of October and the first few days of November.

But that water likely won’t reach far south on the river for a week or two, and no more rain is expected for the next 16 days, he said. The result is that once that light spot passes through the New Orleans area, the river will likely continue lower or at least remain as low as it is now in November.

Officials from the New Orleans Board of Sewer and Water said that water intakes on the city’s east and west banks are low enough into the river not to be affected by the unusually low water levels that occur in the city itself. Once the threshold is complete, it must keep the city safe from the movement of salt water upriver.

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