MOBILE, Alabama—Maintaining the nation’s waterways requires removal of millions of cubic yards of sediment to keep navigation channels safe and reliable. A team at the U.S. Army Engineer Research and Development Center (ERDC) is advancing a different way of thinking about material: rather than treating dredged sediment solely as something to manage, how can it be used as an engineering resource to strengthen coastal systems?
That question is being explored in Alabama’s Mobile Bay, where storms, shoreline change, sediment processes and other environmental stressors have contributed to habitat loss and a decline in oyster populations. ERDC’s Environmental Laboratory, the U.S. Army Corps of Engineers (USACE) Mobile District and regional partners are evaluating whether dredged sediment can be transformed into 3D-printed structures to provide oyster habitat, improve shoreline resilience and expand beneficial use opportunities.
“The real opportunity is to keep sediment working within the coastal system and use it as a resource,” said, Elizabeth Godsey, an USACE Regional Sediment Management and Engineering with Nature Practice Lead. “By combining dredged material with innovative design and printing methods, we can develop solutions that support navigation, restore habitat and increase coastal resilience”.
Oysters have long played an important role in coastal Alabama as a keystone species and driver of economic development and ecology in the region. They are pivotal to the function of Alabama’s estuaries through enhancements of water quality, offering habitat for other ecologically and economically important species, as well as influencing nearshore waves and sediment processes.
Engineers with the USACE Mobile District got the idea to replicate oyster reefs when they were introduced to ERDC’s 3D printing technology and its design freedom, which can mimic nature’s architecture and rapidly produce 3D-printed prototypes
“The idea came from observing how oysters naturally build reefs,” Godsey said. “As oyster reefs grow, they filter and stabilize sediment while creating complex habitat. We asked whether we could use the same system’s sediment already in the navigation channel as a building material to create structures that encourage new reef development.”
Researches from ERDC-EL used sediment collected from the Blakeley Island Confined Disposal Facility (CDF), to fabricate 3D-printed oyster structures. The team developed a printable sediment-based mixture to produce domes that varied surfaces, openings, and internal geometry intended to provide stable substrate and habitat complexity.
“We are using fine-grained dredged sediment from Mobile Harbor as building material,” said Dr. Al Kennedy, a research biologist with ERDC-EL. “The sediment that we collected from the Blakeley Island Confined Disposal Facility can restore CDF capacity after being scaled up. The layers and complex geometry of the printed domes provide microhabitats and surface structures that are ideal for larval colonization.”
The oyster domes are showing promising results, as Kennedy said the nature-inspired structures are attracting barnacles and oysters — adding value to the coastline they currently serve.
“The 3D oyster reefs are holding up and resilient to tides,” said Kennedy. “Barnacles and Oysters are shown to like colonizing on the printed dredged sediment structures as much as the ideal reference material, terracotta. The models provide hard substrate where they previously didn’t exist, expanding the oyster population. The oyster reefs also provide wave breaks and energy reduction while retaining more coastal sediment and reducing erosion.”
Future phases of this project include analyzing oyster engagement with the sediment and immediate on-site 3D printing.
“We plan to compare structural durability and oyster colonization rates of all dredged sediment domes and domes that contain 10 percent oyster shell and 90 percent sediment,” said Kennedy. “We will also use a hopper to continuously print sediment into structures, habitat structures and building materials. Additionally, we strive to print on-site and on-demand to reduce transportation costs and discover bio-inspired binders for the sediment.”
“Every year we move millions of cubic yards of sediment to maintain our nations waterways.” Godsey said. “The opportunity before us is to keep more sediment working within a coastal system, where it can continue providing ecological and engineering benefits. Projects like this help redefine what beneficial use can look like in the future”.