EA is a leader in the design and application of thin layer placement of dredged material to help restore coastal marshes impacted by rising sea levels. Thin layer placement broadly encompasses the purposeful placement of sediment or dredged material in a manner that produces a specific layer thickness or ground surface elevation necessary to achieve overall project objectives. The application of dredged material on a stressed marsh system helps to maintain or improve the receiving habitat’s ecological functions and coastal resiliency. EA has been working closely with federal and state agencies and non-government organizations at marshes impacted by rising sea levels and an increase in severe storms.
When designing a thin layer placement program, several elements must be balanced. When resiliency is the driver (versus navigational channel improvements), data collection and design/engineering are very different than traditional dredge material disposal efforts. Balancing wide ranging variables such as micro-tidal areas, accounting for sea level rise, and the fact there is typically much more dredge material to be disposed of than is needed for restoration are critical in a successful design. Use of a Multi-Criteria Decision Analysis tool for evaluating a wide array of design variables helps in the final design. Field surveys and working closely with stakeholders to ensure appropriate biological elevations are identified ensure a successful design. During construction, the following are important considerations:
- Application of <6 inches (typical) of sediment
- Typically coupled with a navigational channel dredging project
- Application can be aerial or lower pressure ground application
- Avoiding damage to surrounding receptors
- Sorting of grain sizes.
In 2018, 30 participants attended a technology transfer workshop at EA’s Hunt Valley, Maryland office focusing on the challenges of designing and constructing thin layer placement projects. Attendees included the U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, state agencies, non-government organizations, and contractors.
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