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DredgeWire Exclusive: Scientists Reassess 40-year-old Dredged Sediment Beneficial Use Projects

Posted on June 2, 2023

By Judith Powers

A wetland feature dominated by Western grasswort (Lilaeopsis occidentalis) and Water Smartweed (Polygonum amphibium) at the Miller Sands study location in Oregon adjacent to the Columbia River navigation channel. The mainland can be seen in the background.

The team found the sites still functioning and thriving because they were created using natural elevations and inundation gradients, amending the soil, and planting native vegetation. The sites have evolved through natural processes to provide high habitat values as well as wider benefits to the community, which should promote expanding beneficial use solutions for dredged sediments.

The earliest habitat improvement projects constructed using dredged sediment for which monitoring data are available were created from 1974 through 1978 by a US Army Corps of Engineers team led by Mary Landin in locations adjacent to navigation channels throughout the lower 48 United States.

Landin and her team designed the projects to mimic the characteristics of local habitats (elevation, soils, and vegetation), graded the sites, amended the soils, and planted a variety of species to enhance habitat for a variety of species. Results were monitored for up to 10 years to document the effectiveness of the projects over time. In 1986, Landin and her team performed an in-depth analysis of the sites’ vegetation, birdlife, and soils, and published the findings in a 1989 report. The team created 11 dredged sediment habitat areas, most of which were still in existence and performing beyond expectations.

They were scientists with the US Army Corps of Engineers Waterways Experiment Station, now the Engineering Research and Development Center (ERDC) in Vicksburg, Mississippi.

The Engineering With Nature® (EWN) initiative developed by the US Army Corps of Engineers Engineering Research and Development Center (ERDC) incorporates many of the principles used by Landin’s team as they designed sites to survive the dynamic coastal environments in which they are located.

Jacob F. Berkowitz, Ph.D. is a research soil scientist and wetland team leader at ERDC and an adjunct professor at the Louisiana State University College of the Coast and Environment. He is a Certified Professional Soil Scientist, (CPSS) and certified by the Professional Wetland Scientists. (PWS).

Field data collection required a diverse team of experts including (from left) Research Forester Nathan Beane, Soil Scientist Jacob Berkowitz, Botanist Kevin Philley, and Avian Ecologist Jake Jung, all of ERDC, pictured at the Drake Wilson Island, study site in Florida. The foreground consists of a smooth cordgrass (Spartina alterniflora) dominated high marsh, while low marsh and pine dominated maritime forest habitat can be seen in the distance. (Photos by Nathan Beane)

Along with his ERDC team, he recently assessed six of Landin’s documented habitat improvement projects to document multidecadal changes in the soils, bird life, and plant communities 40 years after the sites were developed, and to identify the features of each site that align with the present day EWN initiative. These include evaluations of ecological function as well as economic considerations, social implications and other factors that have been dubbed “ecological goods and services.”

“The quantification of ecosystem functions, goods and services supports the construction of more dredged sediment beneficial use projects, promoting broad public acceptance and justifying funding requirements. Some of the ecosystem functions, goods and services examined include shore protection, wildlife habitat, navigation maintenance (including dredged sediment beneficial use), and recreation and other public uses,” Berkowitz explained.

Research Botanist Kevin Philly collecting vegetation data at the Buttermilk Sound study location in Georgia. He is in a stand of big cordgrass (Spartina cynosuroides) and sturdy bulrush (Bolboschoenus robustus).

He aims to document the full suite of positive project outcomes associated with dredged sediment beneficial use activities in order to further expand the approach to meet the nation’s navigation requirements while improving environmental and societal outcomes. With approximately 35 percent of the dredged sediments undergoing beneficial use today, recent initiatives suggest that up to70 percent of the dredged sediment in the United States could be placed beneficially to build wetlands, nourish beaches, construct/restore barrier islands, and other applications that benefit coastal communities by the year 2030.

Landin’s reports provide rare documentation of four and five decades of functioning artificially created wetland habitats, and Berkowitz saw an opportunity to build upon and add to the understanding of the projects by re-creating the 1989 study at six of the 11 islands Landin created.

“I was aware of the previous research for some time but got really interested in recreating the study around 2016 to address questions about the long term benefits of Natural and Nature-Based Features and similar initiatives gaining momentum,” said Berkowitz. Funding was secured from the Dredging Operations Environmental Research (DOER) and Engineering With Nature® programs. Planning and logistics began in 2018”, Berkowitz told DredgeWire.

“We started by thoroughly reviewing the studies conducted by Mary Landin, Charlie Newling, and others in the 1970s and 1980s,” Berkowitz explained. “Based on those publications, we identified a geographically and ecologically diverse grouping of projects to revisit. At each study location, we recreated as many aspects of the historic studies as possible. For example, we used the same techniques to measure vegetation and characterized the same soil parameters. We also evaluated avian community composition using the same visual and listening surveys as the earlier studies.”

“Project execution required botanists, foresters, avian ecologists, GIS expertise, laboratory personnel, and soil scientists due to the different data streams used in the historic studies,” he explained. “The ability to bring together teams of researchers with these diverse capabilities is unique to ERDC within USACE and much of the DoD, and was essential to achieving our objectives,” he said.

Using this approach allowed the team to compare the original data to the current data, and to compare project sites to “natural” reference areas (selected by Landin’s team) in each location to see multiple decades of ecological succession in the altered project areas differed from the unaltered reference areas.

Research Soil Scientist Jacob Berkowitz holds a soil sample at the Miller Sands study location in Oregon. Note the presence of stratified layers indicating the site is trapping sediment during high water events and the dark soil colors indicating organic matter accumulation.

“This required quite a bit of complex logistics and planning, working with local partners at USArmy Corps of Engineers Districts to gain site access, and extensive data analysis to generate the required information and crosswalk our findings with the original study outcomes,” said Berkowitz.

All sampling took place during 2019. It took two years to get the sample processing, data analysis, writing, and publications completed, Berkowitz explained.

The chosen habitat improvement projects included a wide variety of landforms and habitat types such as tidal and freshwater wetlands, woodland forests, upland meadows, and sand dunes.

The Bolivar Peninsula, Texas project in the Galveston District is an 11.1 hectare (27.4 acre) dredged sediment placement area on the Peninsula adjacent to the Gulf Intracoastal Waterway. Landin’s team contoured the area in 1976 to support upland, high marsh, and low marsh intertidal habitats.

This site aligned with the EWN framework by using elevation gradients and vegetation typical of the region, which allowed tides and sediment accretion to allow the ecology of the site to evolve with no human interference. They also noted that no hard infrastructure such as walls or berms were used. Present day observation holds that hardened structures alter other ecological functions and processes.

Drake Wilson Island, Florida in the Mobile Districtis a five hectare (12.3 acre) area where dredged sediment was previously placed. In 1976, Landin’s team introduced fine-grained silty dredged sediment from the neighboring Two-Mile Channel to develop an emergent marsh where native vegetation was transplanted from a nearby reference area. Landin reported that in two years the area was almost completely covered in vegetation and was supporting healthy wildlife populations at the conclusion of her study in 1986.

The 2019 survey found that the island has kept its diverse habitats, including natural sand deposits, upland maritime pine woodlands and high-quality march habitat, on which least terns, clapper rail, willet, great blue heron, marsh wren, boat-tailed grackle, bald eagles, brown-headed nuthatches, and osprey are thriving, among other species.

Using fine-grained dredged sediment that mimicked substrates common in other marshes in the region, allowing natural tidal exchange, sourcing the vegetation locally and leaving nature to drive sediment movement and natural species succession are features of EWN that exist in this project.

Buttermilk Sound, Georgia in the Savannah District is an area adjacent to the Atlantic Intracoastal Waterway (AIWW) where a 2.1 hectare (5.2acre) mound of dredged sediment approximately five meters high was chosen for alteration. The goal was to show that sandy dredged sediment could support a stable marsh.
Landin and her team graded the sand to marsh-supporting elevations and planted it in local marsh vegetation. After five years, Landin reported that the area was a thriving marsh visually indistinguishable from unaltered marshes.

The 2019 study found low marsh, high marsh and unvegetated upland habitats at the site.

The EWN features of this project were the creation of marsh-supporting elevations and allowing natural processes, including tidal creek evolution to occur over time.

Nott Island, Connecticut is a 3.2 hectare (7.9 acre) dredged sediment placement site used for maintenance navigation operations from the Connecticut River channel. The project is located in the US Army Corps of Engineers New England District.

In 1974 the pile had reached several meters high, creating a steep, unvegetated sand mound with little habitat value.

Landin’s team graded the sand to create an upland meadow, incorporated fine-grained dredged sediment to improve soil quality, and augmenting it with lime and fertilizer. Plantings to create bird habitat were introduced, and 80 percent of the project area was vegetated within the first growing season.

EWN features included incorporating finer grained sediment into the sandy dredged sediment to match the soil in other habitats more closely, and leaving the site to nature, allowing other local plants to naturally migrate into the area, which became an important and productive bird habitat.

Pointe Mouillee, Michigan is the site of a 148 hectare (365.7 acre) diked dredged sediment management complex in the Detroit District designed to protect an extensive marsh complex from wind and wave driven erosion on the southwest shore of Lake Erie. It replaced an original barrier island that washed away in storms and high water in the 1960s, causing degradation of more than 1,1618 hectares (3,998 acres) of marshland along the shoreline.

More material was deposited from nearby shipping channels to create a marsh to protect the shoreline marsh and a serve as a confined disposal facility (CDF) for maintenance dredging sediments from the Lake Erie navigation channel. In addition to providing valuable habitat and protection from storms, the site also supports a visitor center and hiking, hunting and bird watching opportunities for the general public.

Landin reported that plant colonization in the marsh was complete within three growing seasons.

The 2019 study found that the project is still a healthy freshwater marsh habitat after more than 40 years of ecological succession.

The site protects the remaining marshes, provides habitat and recreational opportunities for the public, and continues to serve as a placement area for regular channel dredging, which are features of EWN that it continues to provide.

Miller Sands, Oregon in the Portland District was a 94.7 hectare (234 acre) historic dredged sediment mound adjacent to the Columbia River navigation channel near Astoria, Oregon. Columbia River sediments were deposited there approximately every four years from 1932 until the 1970s. In 1974, Landin’s team began remediation of the site, and graded it to establish upland meadows, wetland marshes and dunes. The upland portion was disked prior to planting native species and the intertidal areas were planted with native marsh plants. Beach grass was planted on a sand spit, stabilized with sand fencing.

An approximately 10 hectare (25 acre) sparsely vegetated sand spit has developed at the Miller Sands study location in Oregon, where wind and waves form small dunes. The wide variety of landforms present at the dredged sediment beneficial use sites indicates that they are providing diverse habitats and a variety of ecosystem functions, goods, and services more than 40 years after construction.

The EWN features of this project are the provision of multiple habitat types, using elevation and inundation gradients to identify targeted native species plantings. Erosion and sediment accretion were allowed to re-shape the island over time, while the site continued to receive periodic dredged sediment placements in support of navigation channel maintenance.

The team in 2019 found three thriving habitats, upland meadow, tidal marsh, and dunes providing a wide array of ecosystem, functions and associated goods and services at Miller Sands.

Berkowitz reports that most of the project areas displayed increases in total land cover and vegetation abundance and decreases in open water and barren areas. The projects have resulted in the creation of more than 70 hectares (173 acres) of new land since construction. Some of the vegetation species originally planted in the 1970s have disappeared, which the report attributes to natural evolution of plant community succession.

“While broadly successful, opportunities exist to improve the performance of the project sites through selective species control and other management activities including the periodic deposition of new dredged sediment to supplement elevations and support habitat for particular species groups (e.g., ground nesting shorebirds). Establishment of the project provides valuable documentation that these types of dredged sediment beneficial use projects yield long term ecological and societal benefits while promoting the responsible management of dredged sediments across the United States,” he concluded.

Berkowitz and his team have published two reports: “A Multi-Decadal Assessment of Dredged Sediment Beneficial Use Projects, Part 1 and Part 2” providing full descriptions of the processes used and detailed results of the project in the Western Dredging Association (WEDA) Journal of Dredging, Vol. 20 No.1, available on the WEDA Website He presented a Webinar describing his research activities on November 14, 2022, a recording of which can be viewed on the WEDA website as well.

Suggested key words: EWN, dredging; wetland restoration, nearshore, shallow water placement, water quality monitoring, beneficial use, regional sediment management, natural and nature-based features, ecological functions, ecosystem goods and services, ERDC

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