Last spring we were battling some of the worst flooding on record from one end of our District to the other. This year the opposite is true with drought and extreme low water plaguing the Mississippi River and its tributaries.
The Mississippi River gage at Memphis climbed to an astonishing 48.08 feet in early May last year. At the end of August this year it dipped to minus 9.8 feet.
“That’s almost 58 feet of difference,” Dave Berretta, Memphis District Chief of Hydraulics and Hydrology (H&H), said. “That’s the height of a six-story building.”
So how did we get from flood to drought in just a year? The weather experts have mixed opinions. Some say natural climate variability is the culprit. Others blame it on man-made global warming. A prime suspect is La Niña – a cooling of the surface water of the eastern Pacific Ocean that in turn brings drier weather to the Midwest.
Whatever the cause, it has presented the Memphis District with plenty of problems this summer.
“We first started seeing problems around June 1 when already low gage readings continued to drop, mirroring the 1988 low water event,” Steve Barry, Chief of Memphis District’s Readiness and Contingency Operations Branch, said.
According to Don Mayer, Navigation Section Chief, these low stages have brought problems to river navigation in two areas: the Mississippi River mainstem channel and the ten river harbors the Memphis District is responsible for.
“Shallow water in a few reaches of the river here in the Memphis District has slightly increased the number of towboat groundings this summer,” he said.
Mayer said the Corps – working in cooperation with the U.S. Coast Guard and the towing industry – has used several tools and techniques to meet these challenges. These include:
• Light-loading barges to slightly shallower drafts and pushing fewer barges in tows.
• Mainstem dredging by the Memphis District’s dustpan dredge Hurley in low water “hot spots.”
• Closely working with our counterparts in the Corps’ Great Lakes and Ohio River Division to adjust outflows from reservoirs to keep river levels up.
• The system of stone dikes and concrete revetments the Corps has put in place over many years to help the river maintain flow velocities and reduce the amount of sediment that settles in the channel.
“The bigger problem has been with our harbors,” Mayer said.
Although all harbors in the Memphis District have received funding for dredging, we have only been able to put two contract cutterhead dredges to work in the District. Although a few harbors are open as usual, others are either under very light loading restrictions or closed entirely.
In the northern part of the District, the dredge Venture has worked in several harbors including Elvis Stahr (Hickman), Ky.; New Madrid City and New Madrid County, Mo.; Caruthersville, Mo.; and Northwest Tennessee (Tiptonville), Tenn.
To the south, the dredge Pontchartrain is working at McKellar Lake (Memphis). Later this fall, it or the dredge Venture will move to the harbors at Helena and Phillips County in Arkansas. These last two harbors are currently closed due to the low water.
Although the low water conditions this year have approached gage readings close to the record set in 1988, River Engineering’s Derrick Smith said we are in much better shape to deal with the situation now than we were then.
“We’ve had almost 25 years to study what happened in 1988 and to apply those lessons by building dikes and other structures to manage and train the river,” he said. “Even if we were to reach or surpass the minus 10.7 feet record of 1988, I don’t think we’d see the severe river closures and groundings like we did then.”
According to H&H chief Berretta, historically we can look for river levels to slowly begin climbing in about the November timeframe. Until then, we’ll continue to take whatever steps are necessary to keep the river open and make improvements to the system.