USA: Army’s Oldest Dredge Creates New Habitat

The endangered Least Tern has a new island to call home on the Mississippi River thanks to the U.S. Army Corps of Engineers – St. Louis District, the Dredge Potter and a flexible, floating dredge pipe.

Historically, the Least Tern nested on sandbars along the Mississippi River. The establishment of navigational pools, repeated flooding and an increase in recreational activities along the river has led to the decline of the population.

As part of a pilot project during this year’s dredging season, the St. Louis District reused dredged material to build small islands using a flexible floating dredge pipe.

“The flexible floating dredge pipe provides the St. Louis District opportunities to create a diversity of aquatic habitats such as sand islands and shallow water habitats in areas where it may not be possible without the use of dredged material,” Brian Johnson, biologist with the St. Louis District said.

Each year dredging is performed on the Mississippi River in order to keep it open to the Congressionally mandated depth for river traffic. Historically, dredged material placement locations and options have been limited by both equipment constraints and cost.

When feasible, dredged material is recycled for beneficial uses within the river. Reuse is the preferred approach by the Corps of Engineers, and the St. Louis District is always seeking out innovative and creative ways to accomplish this task.

“Our partners and stakeholders have challenged us to find more ways to reuse dredged material in an environmentally friendly way,” Johnson said.

The Potter crew spent most of the off season prepping the dredge for the use of the flexible floating dredge pipe.

“It took a lot of planning ahead and creative ideas to make this happen,” Lance Engle dredge manager with the St. Louis District said.

Traditionally, the use of standard dredging practices limited the opportunity to reuse dredged material as sandbar or island habitat because of the physical limits of the rigid metal disposal pipe that is used.

“Normally dredged material is side-cast along the main channel border in a linear fashion, resulting in a long, narrow disposal bar that is limited in size, elevation, and location,” Engle explained.

 A St. Louis District experiment with flexible floating dredge pipe in 2005 led to the idea of using it to create islands and sandbars on the Middle Mississippi River. Demonstration projects by the New Orleans and Mobile Districts helped develop the idea and prepare the dredge crew for the new challenge.

The pipe’s flexibility allows the Dredge Potter to place dredged material in a specific location as it moves. This allows material to build up to create sandbars and island habitats in various shapes, sizes and elevations in the Middle Mississippi River while maintaining the navigation channel.

These types of habitats are essential for the nesting and spawning of various fish and wildlife species such as the Least Tern.

“The new method allows creation of more diverse environments for wildlife than traditional dredging methods,” Johnson added. “These islands are often remote, providing protection from predators, boats and humans.”

The flexible floating dredge pipe allows the St. Louis District to keep the river safe and open for navigation in an environmentally sensitive way.

“In the future, we hope this will be the way we do business,” Johnson said. “Eventually we hope to use the Dredge Potter not only for navigational purposes but for environmental management purposes as well.”

[mappress]

Dredging Today Staff, December 15, 2011; Image: army