A Muscatine surveying and engineering firm is playing a key role in the multimillion-dollar effort to keep the Mississippi River open for barge traffic in the area of Thebes, Ill., where record-low water levels have exposed hazardous rock formations.

Martin-Whitacre Surveyors & Engineers Inc. is collecting and providing survey data on what the bottom of the river looks like to a Dubuque-based marine services company that is doing the actual rock removal for the U.S. Army Corps of Engineers. Keeping the river navigable is vital, with shipping and commodity interests saying that billions of dollars worth of products move down the Mississippi.

Matt Krause, a partner in the Muscatine firm, and his son, Merrick, have been on the river about 150 miles south of St. Louis every day since Dec. 15, except a three-day break for Christmas.

Every morning, they set out on their 20-foot-long, commercial flat-bottom boat with an echo-sounder — a $100,000-plus piece of equipment about the size of a shoebox — mounted on a rotating arm on the side.

They lower the echo-sounder into the water, where it sends out a multi-beam of “pings,” scanning the bottom by picking up data points captured by sound waves.

The two work in grids of 150 by 350 feet, making 10 to 12 parallel passes. Each pass covers a stretch 20 to 30 feet in width, and each pass overlaps at least 50 percent, Krause explained by telephone Wednesday morning before heading out for the day.

That work takes perhaps 25 minutes, but then the raw data must be processed in a computer, the points converted to elevations and corrected for the heave, pitch and roll of the boat.

Once that’s done, the information is handed off to an operator from Newt Marine Services of Dubuque, who puts it in his computer.

Newt Marine is one of two main contractors in the area, operating three rigs. Each consists of an excavator on a barge pushed by a towboat. The excavator buckets are up to 10 feet wide and can pick up boulders 7 to 8 feet in diameter and as heavy as an estimated 15,000 pounds.

“Just like on land, the arm (of the excavator) reaches to the bottom, except they’re blind,” Krause said of the operators. “They can’t see what they’re doing.” They rely on the survey data to show them the bottom.

Sometimes, rocks can be rolled along the river bottom to deep pockets of 20 to 30 feet, while other times they are picked out of the water, loaded onto material barges and taken to a disposal area, said Dan Arnold, the construction manager for Newt Marine.

Excavators usually do not get everything the first time, so both they and the surveyors have to go over an area repeatedly until they are certain it is free of protruding formations, Krause said.

The six-mile area near Thebes where they are working is known as the Little Chain of Rocks, said Mike Petersen, chief of public affairs for the St. Louis District of the Corps of Engineers. In 1989 — the last time the river experienced very shallow levels — the Corps blasted 200,000 cubic yards of rock out of the area to make it navigable, he added.

But they knew even then that some rocks remained and that they eventually would want to remove those. The work is making the navigable channel deeper and wider, which is important because there is a curve in the area that tows must navigate, Petersen said. In the lower stretch of the Mississippi, tows of 30 to 40 barges are common — compared with 15 in the upper part of the river that includes the Quad-City area — so it’s like “a city block being pushed downriver,” he said.

So far, Newt Marine has not had to do much blasting, but the company has drill rigs and blasting equipment in the area and expects to do more before the job is complete, Arnold said.

The Muscatine company and Newt Marine are working north of the Thebes bridge; another surveyor and marine firm are working south of the span. While they are working, barge traffic stops and lines up.

Then, about 8 or 9 p.m., the towboats can begin moving again. So far, “the queue has cleared every night” and there are no backups, Petersen said.

Overall, the rock-removal work is estimated to cost $9 million to $10 million, which the Corps is paying out of pocket, he said.

“It’s money we had budgeted,” he said. “We’re borrowing from other projects.”

In addition, two Corps dredges have been dredging — sucking up and moving sand — 24 hours a day, seven days a week for the past six months in the middle Mississippi, the area between the confluences of the Missouri and Ohio rivers.

The Muscatine firm’s contract extends through Jan. 23, although the work could get done sooner, Krause said.

When he started, their boat did not have a cabin, so they worked in below-freezing temperatures with occasional rain and snow. They got a custom cabin around Christmas, which has made the work easier.

“Now we’re inside and it’s considerably more pleasant,” Krause said.

The engineering firm bought the boat and echo sounder specifically for this job. The equipment, including hardware and software, cost about $120,000, Krause said. The company considers it an investment, expecting to use it in the future.

Petersen praises their precision.

“They can find a rock the size of a glove,” he said. “The amount of detail is amazing.”