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Shannon County Road 401 Crossing

Emminence, Missouri

Stream Crossing

Owner:

Shannon County Commission

Engineer:

Missouri Department of Conservation

Contractor:

Shannon County Road Department

Installation:

December, 2010

Shannon County Road 401 leads from Eminence southwest to Delaware and crosses Mahan Creek. Mahan Creek is a tributary to the Jack’s Fork River, which is part of the Ozark National Scenic Riverways and considered an Outstanding Water Resource by the Missouri Department of Natural Resources.

The previous crossing was a low water ford, consisting only of a natural stream gravel bed. After high flow or flooding events, the county was continuously repairing the road to fix extensive damage at the unstable crossing. In addition, vehicles belonging to local residents would get stuck in the crossing due to the unstable nature of the gravel. This continual disturbance presented a large problem for the local residents, a maintenance headache for the county road crews, and ultimately added to gravel accumulating in the Jack’s Fork River.

“We needed to find a solution on a dynamic section of stream that would improve the stability of the crossing for local residents and minimize the continual maintenance needed by Shannon County road crews, while not impeding aquatic organism passage in the stream,” stated Dave Woods, Fisheries Management Biologist with Missouri Department of Conservation (MDC).

In Fall 2009, Shannon County road officials and fisheries staff met at the crossing to discuss the County’s continuous maintenance problem, as well as the resulting effects on stream health and water quality of Mahan Creek and the Jacks Fork River. Between the County Commission’s concern for accessibility and safety for the local residents, and MDC’s interest in maintaining healthy stream dynamics, a partnership was formed to try and address the problem. MDC staff secured a grant from the Missouri Conservation Heritage Foundation through their Stream Stewardship Trust Fund to purchase materials for an articulating concrete mattress crossing (ACM). Specifically, 2,400 feet of ArmorFlex® class 50-s mats were chosen as the solution and their interlocking design cabled together to form a mattress. These mattresses were then installed in the stream bed to provide a stable low water crossing for vehicles. The design allowed for the passage of sand and gravel over the crossing during high flow events, while maintaining stability after flooding. The ArmorFlex design allows for adjustment to the natural shifting and settling of the stream bed during high flows and, as a low water crossing, provides a surface for aquatic organism passage.

Contributing partners of this project included funding for the ArmorFlex materials from the Missouri Conservation Heritage Foundation, installation of the crossing by the Shannon County Commission, and engineering design and technical guidance from the Missouri Department of Conservation. Through the contributions of these three partners, the new crossing was installed in December 2010. This project provided a good example of how the goals of different agencies and organizations can overlap to create strong partnerships and new solutions to old problems.

“After the base rock was placed, installation of the mattresses was pretty simple,” added Mr. Woods. “As long as you have a mobile piece of equipment that can hoist the ACM’s, the project can be completed rather quickly. So far, this crossing has experienced heavy flooding in the spring of 2011, and it has performed as we had hoped.”

The Missouri Conservation Heritage Foundation is a nonprofit, charitable organization that helps meet financial needs placed on natural resource conservation and conservation-related outdoor recreation. Since being founded in 1997, MCHF has allocated more than $9 million for conservation funding statewide.

Technical Description:

  • Products: ArmorFlex® class 50-smat; 8’ x 20 ‘
  • Area: 2,400 sf
  • Units: 50

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