Harbor hemi-marsh

*This project was undertaken with the Ohio EPA and USACE Buffalo District as part of Healthy Port Futures. For a more detailed explanation of the project see the HPF website.

The inner harbor of Ashtabula, on the protected side of the breakwater sediment is being placed using an adaptive, open concept to create a dynamic hemi-marsh using a partially open structure.

This project serves as one of the initial attempts in the Great Lakes to construct a partially-open wetland system with dredged material through the Section 204 program. A submerged sill works in conjunction with the established harbor breakwater to protect the placed dredged sediment and allow for wetland establishment. Over the course of many cycles, the area inside the sill will be filled with local dredged material to support wetland and lake-floor habitats that benefit both aquatic and terrestrial wildlife and create recreational and tourism opportunities for the region.

Moving away from a more standard practice of “confined” sediment placement, the project in Ashtabula recognizes the value, both economic and ecological, in a more open, sensitive, and passive type of coastal infrastructure. While it still maintains a relatively conservative amount of protection, the concept was to work closely with the USACE to encourage the highest level of openness possible while landing within acceptable levels of project risk.

This partially-open design facilitates the occasional, ecologically-necessary disturbance that will facilitate wetland complexity while also allowing for an important hydrological connection to the nearshore. The placement of sediment will take place over three or four dredge cycles, occurring every two to three years. Since the project will occur over a series of cycles, adaptive management can be employed to help inform the strategy. Placement of sediment will depend on the angle of repose and settling rate of sediment, which is best quantified in the field. After each placement, monitoring will occur to inform the next placement cycle. Thus allowing for a responsive management approach.

Strategies developed from this project have scale-up opportunities for larger ports and scale-down opportunities for smaller ports. The project is currently constructed and initial cycles of placement are occurring using the dynamic hemi-marsh concept.