How low can it go? It’s a tough question for engineers and port officials to answer as the Mississippi River fell another tenth of a foot this morning, to 1.16 feet.

The record depth of the river in Vicksburg is negative 7 feet on Feb. 3, 1940. Low negative levels on the local gauge were recorded in 1964 and 1988, the latter of which occurred during a dry, scorching summer much like 2012.

Placing a firm “floor” to what’s considered safe for navigation is dicey, said the Corps of Engineers Vicksburg District, busied to the max since late June as it dredges shallow ports in the Lower Mississippi.

“No one wants to answer that one,” Corps spokesman Kavanaugh Breazeale said Tuesday after hydraulics and water control experts met. “They say it’ll be when barges run aground.”

A “minus” reading does not mean the river is dried up, as it’s simply a measurement of how the river gauge is designed. A “zero” reading reflects when the main navigation channel falls to about 46 feet, a level that shrinks with heavy, cargo-laden barges atop it. No closures are pending, even with a tenth of a foot stage predicted by mid-August.

Austin Golding, co-owner of Golding Barge Lines, said areas north of Vicksburg between Cairo, Ill. and Greenville — identified as the tightest squeezes for barges by industry watchers — are a much bigger challenge for towboat pilots than in Vicksburg, where the main channel is deep enough to guide grain and petrochemical barges through the piers of the river bridges.

“Vicksburg is not going to be a real problem area, in my opinion,” Golding said from a meeting in Houston with the company’s 12 towboat captains. “It’s a deep channel. As far as our tows go, it won’t be an issue. It’s a very deep section right there. The sandbar on the Louisiana side is the only question mark. But, the Corps has been dredging.”

Twice in the past month, the Dredge Jadwin has removed silt from the river bottom near the Madison Parish Port, located on the main stem of the river. Corn, gravel and sand loads are moving again after a sharp slowdown due to the low water, said port director Clyde Thompson.

“It was the worst I’d seen it,” said Thompson, director since 1989. “A lot of the farmers bring that corn in to Bunge’s dock and our dock. We’ll do what we can do.”

The Port of Vicksburg will be dredged in September once the Jadwin returns from stops upriver in Greenville and Yellow Bend, Ark., part of more than $6 million in emergency dredging on the Lower Mississippi. Shipments of steel coil, corn and other materials at the inland port were up 31 percent for the year, through June.