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Long-Awaited Project To Deepen MKARNS To 12 Feet Begins

September 1, 2023   The Waterways Journal

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A channel-deepening project that has been talked about for 20 years is underway on the Arkansas River. The Tulsa and Little Rock Engineer Districts have begun a required environmental study to guarantee a navigation channel of the Arkansas River to 12 feet along a 445-mile length.


The 12-foot depth was already authorized in 2004, but it was never previously funded. The current project was able to be initiated thanks to $96.6 million in funds from the Bipartisan Infrastructure Law, also known as the Infrastructure Investment and Jobs Act, received in March. The project was authorized by Congress in 2005 but was given no funding at the time.


In February, the Little Rock District received an added $4.1 million in the Fiscal Year 23 Work Plan. On March 3, the district allocated $3.3 million in operation and maintenance funds to provide reliable navigation on the MKARNS. The design phase will last until 2025, when the construction phase will begin.


According to Edmund Howe, chief of hydrology and hydraulics for the Little Rock Engineer District, the depth of the Arkansas River can vary from 9 feet to more than 50 feet in places. As much as 85 to 90 percent of the river may already be at 12 feet or deeper. But even 10 percent of a 445-mile-long river bottom is a lot of material, he said.


The last full-scale study of the Arkansas River was done in 2005. A lot has happened since. Major floods in 2008, 2011, 2015 and especially the historic floods of 2019 have changed the riverbed. River-scanning technology has improved. Many weirs and river-guidance structures were degraded in floods and had to be rebuilt.


The new study will locate trouble spots that require channel dredging. “That’s what we’re in the throes of right now,” Howe said.  A multi-beam survey of the river bottom was done recently, using sonar to map the river every 3 feet. “It’s like a really expensive fish-finder,” Howe joked. “It’s the most comprehensive picture ever taken of the river bottom.” His team is also looking at past river data, going back to the 1940s.


The design phase will last until 2025, when the construction phase will begin. The construction phase will be a combination of dredging at hot spots and building rock weirs and wing dikes to channel the river water and get it to scour the channel. Dredged material may be used to build habitat islands. The upstream Tulsa District has more room to place dredged material on shore sites, Howe said. The two districts share a dredging contract for maintenance dredging.


Howe spent several years in the Memphis Engineer District working on the hydrology of the Mississippi River before returning to his hometown of Little Rock as chief of hydrology. He said the Memphis District sometimes helps the Little Rock District with expertise and equipment.


Arkansas River flows are partly regulated by upstream reservoirs in the Tulsa Engineer District. River training structures work best at flows of between 60,000 and 70,000 cubic feet per second, he said. After heavy rainfalls, when flows get higher, the Tulsa District can taper its releases to provide some relief to shoaling conditions.


Deepening proponents have long argued that a deeper channel would unlock the fuller potential of the McClellan-Arkansas River Navigation System, allowing barges to carry 43 percent more cargo. The Corps has estimated that once the deepening is completed, it will increase the productivity of the MKARNS by 30 to 40 percent. About $5 billion in goods a year moves along the system.