ASHTABULA

Similar to another Healthy Port Futures project in Lorain, Ashtabula is a mid-sized port harbor located in the Lake Erie’s central basin, and the site of a 204 project collaboration between the Army Corps of Engineers and Ohio EPA.  These 204 projects, which create wetlands from dredged material, are the marriage of two desired outcomes for the state of Ohio: To both reduce the amount of open lake placement in Lake Erie and to create wetlands along the coast. 

Healthy Port Futures joined the project post-site selection during feasibility to aid in the design and construction of the wetland.   Sited inside the protected harbor mouth, the project involves the connection of two sides of the existing breakwater through the construction of submerged sill.  To create topography that will support wetland habitat, the area inside the sill will be filled by dredged material over the course of multiple cycles.


CONCEPT


Through passive sediment management, HPF initially conceived of an open sill design that could create a range of wave environments.   As areas within the wetland become more or less susceptible to erosion and accretion, these differences in wave protection could help generate wetland complexity. Additionally, this more open system would maintain important hydrological connectivity to the lake.

Due to the possibility of reducing costs, the design of the project is heading toward a more open system that embraces the principles of passive sediment management. As it stands currently, the southern end of the wetland will be open, while the northern and western sides will be protected by the existing breakwater, and the eastern side by the submerged sill.  This construction will lead to differences in wave conditions, and the placement of the dredge material informed by this varied environment.   


PROCESS


In order to work through different design alternatives, Healthy Port Futures simulated a series of potential outcomes based on a set of constraints; angle of repose of the sediment, amount of sediment in a placement cycle, current bathymetric conditions, and the sill and breakwater height.  From these set conditions, a series of design outcomes could be generated by varying the amount and location of dredge placement sites within a cycle.  

Importantly, the angle of repose of the material in the environment is currently an estimate.  This environmental unknown, and others like it, necessitate a more adaptive management approach.  Since angle of repose dictates the capacity of the cell, as well as the potential height of the material, it is linked to a range of values such as navigation and habitat creation.  While both digital and physical modeling have been done to help inform the physical performance of the material, data collected about the angle of repose during the initial placement cycles will also inform the subsequent placement.