Dredging Creates Diversity in Iowa

“Diversity is a good thing,” project manager Tom Novak of the US Army Corps of Engineers (USACE) St Paul District said, when talking about the natural diversity resulting from a dredging and construction campaign at Harpers Slough on the Mississippi River in Iowa. The project is creating river islands that protect other islands, all of which help migrating waterfowl, fish and aquatic vegetation.

The project is providing “key features that enhance the quality and diversity of river habitat”. And it is one of a number of environmental beneficial initiatives in America’s Midwest that are applying dredging, related construction, and other means to address various environmental issues.

In fact, dredging and island and dyke construction are right at the core of the response at Harpers Slough, and in this instance that means using dredged material and rock to create long, narrow barrier islands around existing island remnants. The works will enhance habitat along the shore, on land, and in shallow water between the new islands and the remnants they protect. Also on the construction agenda is the building of five sills and mounds as part of the protective river complex.

It’s a snapshot of long-standing, continuing efforts in the region to arrest that process and it is part of the Upper Mississippi River Restoration Program spearheaded by the USACE, two states, and US Fish and Wildlife Services, which manages the completed islands.

The USACE calls the Harpers project site “a 1,679 ha backwater area” on the western side of the upper Mississippi River in Iowa. The slough, located in navigation Pool 9 near river Lock and Dam 9, is important to bird and fish life but, according to the USACE, “many of the natural islands bordering the navigation channel and extending into the backwater have eroded and many are disappearing.” That navigation channel was created with its system of locks and dams in the 1930s and extends several hundred kilometres on the upper Mississippi River. The channel had its costs: namely wave and flow action that eroded the islands over the decades.

Work on the USD11.9 million campaign at Harpers started in April 2015 and is projected to be complete in October 2017. The prime contractor is Newt Marine Services of Dubuque, Iowa, with subcontractor Sodko providing tree planting and seeding services, and Bruening Rock Products supplying rock.

Harpers Slough follows the recently completed Capoli Slough island project in Wisconsin, a similarly focused habitat project officially opened in May 2016. That project, as described by the USACE, is “a side channel and island complex” in the Mississippi River that, like Harpers Slough, provides “beneficial habitat for fish and migratory birds” and to “reduce environmental damage caused by the creation of the [2.7 m] navigation channel.”

At the time of writing, technicians were busy at Harpers Slough wrapping up the construction of a 42.6 m-wide, 832 m-long island and placing protective rock. The next step will be building another three islands nearby.

For the Harpers initiative, technicians have used mechanical and hydraulic dredging for two kinds of material. First, they are dredging granular material from certain areas of the nearby main channel, USACE resident project engineer, Scott Baker, explained. The material, sand, “is a good base for islands,” he saids, and is placed hydraulically. Second, fines, mostly clay with some silt, are dredged mechanically and used as topsoil on newly constructed islands. The approach works well, with Baker noting, in fact, “after drying, this is excellent topsoil”.

There’s been a fleet of equipment along the way: Technicians have deployed a CAT 385 excavator with a 4.2 m³ bucket on a dig barge, several material barges, “additional backhoes, barges and tow boats for rock placement and access channel dredging,” and to offload, a PC400 excavator on a spud barge. More recently, Ellicott 1270 and 370 hydraulic dredgers have been used with steel and HDPE (high-density polyethylene) pipe, respectively, along with the aforementioned excavators and barges.

The USACE indicates that 294,353 m³ –that includes both kinds of material—will be dredged this year, which is more than 57% of the project’s expected total of 500,783 m³. In addition, technicians will place 63,503 tonnes of rock during the life of the project.

At Capoli most recently, McHugh Excavating was the prime contractor of a USD3.9-million project that carried out the second stage of that project, with JF Brennan and Kraemer Company on hand as well. That work followed on the heels of the first-stage project in 2011, when Newt Marine implemented a USD4.2 million contract as prime contractor, with Weymiller Marine placing rock and providing marine services support as subcontractor and two companies, Staggemeyer Quarry and the aforementioned Bruening, on hand as rock suppliers. On another point, Capoli recently included public participation: area students helped plant seedlings at the site.

The proactive work is not happening in a vacuum: elsewhere in the Midwest, various entities have also been addressing a wide range of environmental concerns. The USACE Chicago District, for example, has been quite busy on marine and coastal projects, in recent years and currently, that are meeting environmental challenges. District officials recently shared details with IHS Fairplay about an interesting and diverse array, including:

• An ecological dune and wetland habitat restoration effort at Portage Park on Lake Michigan in Indiana. Contractor ENCAP is carrying out planting and other work, according to the Corps.
• An ongoing project to create coastal habitat on a portion of Northerly Island, a manmade peninsula in Chicago.
• Continuing planning for a project to bring ecological sound beach and dune structures, aquatic habitat and native vegetation to Jeorse Park in east Chicago.
• Construction of a permanent electric dispersal barrier to block invasive Asian carp from reaching the Great Lakes. The project, at the Chicago Sanitary and Ship Canal in Illinois, follows the construction several years ago of three initial barriers.
• Annual dredging operations at the environmentally troubled Indiana Harbor—Kokosing/Durocher Marine carried out the 2015 campaign, which cleared 243,282 m³ for placement in a recently constructed confined disposal facility. This year’s dredging is scheduled to start in August. In another CDF initiative, the USACE is studying the feasibility of constructing a CDF at Chicago’s Calumet Harbor and River, another environmentally troubled area that is dredged annually.

Back at the very different environs of Harpers Slough, work continues, with Baker describing many natural benefits for ducks, birds, larger mammals, aquatic life, richer coastline habitat, landside plants and eventually, forests.

Finally, projects such as Harpers Slough are about even more than environmental and navigation issues. The Wisconsin Department of Natural Resources has pointed out those important benefits and more: healthy fish and waterfowl habitats that draw in anglers and hunters, in turn benefiting local economies. And as Baker added, managing these projects effectively ”improves working relationships with partner agencies” generating benefits for other projects, all while helping the public see what river restoration initiatives are all about.

Source: IHS