Ashtabula

Overview

Historically, rivers in Northern Ohio would move sediment through littoral and floodplain wetlands before reaching Lake Erie. Industrial centers and hardened shorelines from development have displaced historic wetlands and created a need for dredging.

The inner harbor of Ashtabula was selected for a wetland creation project that sought to balance the need for wetland establishment, wetland diversity, and amount of dredged sediment utilized.

The inner harbor of Ashtabula was selected for a wetland creation project that sought to balance the need for wetland establishment, wetland diversity, and amount of dredged sediment utilized.

The mid-sized port cities of the Central Basin are located in historical drowned rivermouths, and as such, present similar challenges and opportunities in their sediment management plans.
The mid-sized port cities of the Central Basin are located in historical drowned rivermouths, and as such, present similar challenges and opportunities in their sediment management plans.
In Ashtabula and neighboring Lorain, novel harbor wetlands provide critical reference information regarding the wave protection necessary for establishment.
In Ashtabula and neighboring Lorain, novel harbor wetlands provide critical reference information regarding the wave protection necessary for establishment.
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Purpose

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.

Concept

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.
In the Central Basin wetlands, a hybrid of the two current sediment management options, a semi-open cell wetland merges the ease and cost-effectively of open deep water placement, with wave protection of CDF.

Design

Due to the possibility of reducing costs, the design incorporates a more open system that embraces the principles of passive sediment management. While initially designed to be a completely enclosed system, the USACE, with our encouragement, settled on a design that is open on the southern end. The newly-constructed containment structure, consisting of a submerged sill on the west, sits below water level, while the northern and western sides will be protected by the existing breakwater. 

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.

In Ashtabula, HPF initially drafted an wetland design that called for a semi-open cell system which promoted wetland diversity and occasional disturbance.

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.

In Ashtabula, HPF initially drafted an wetland design that called for a semi-open cell system which promoted wetland diversity and occasional disturbance.

Through the year process, Army Corps of Engineers (ACE) refined their design to include a wetland cell that was open to the more protected, shoreside, and an emphasis on placement which would promote topographic differences necessary for wetland diversity.

Process

After collaborating with the USACE on the physical design of the structure itself, we used both digital and physical modeling to give us insight into how the material will perform. Using a parametric modeling program, we simulated a series of potential outcomes based on a set of constraints: angle of sediment at rest, amount of sediment in a placement cycle, current bathymetric conditions, and the sill and breakwater height. Using these conditions, we generated a series of design outcomes by varying the amount and location of dredge placement sites within a cycle.
We partnered with the University of Minnesota’s Saint Anthony Falls Laboratory to test Ashtabula’s dredged material for the angle of repose under a series of conditions. The angle of repose of the sediment will determine the amount of sediment placed, the slope of sediment, the elevation of sediment. This information helps inform what wetland habitat can be established, and the amount of wetland complexity possible.
Through collaboration with a fluid mechanics research lab at University of Minnesota, Ashtabula's dredged sediment was tested for an average angle of repose.
Through collaboration with a fluid mechanics research lab at University of Minnesota, Ashtabula's dredged sediment was tested for an average angle of repose.
Through Rhino, a modeling software, and the parametric plug-in Grasshopper, HPF explored placement possibilities and resultant topographic diversity based on the material's estimated angle of repose.
Through Rhino, a modeling software, and the parametric plug-in Grasshopper, HPF explored placement possibilities and resultant topographic diversity based on the material's estimated angle of repose.
Through Rhino, a modeling software, and the parametric plug-in Grasshopper, HPF explored placement possibilities and resultant topographic diversity based on the material's estimated angle of repose.
Through Rhino, a modeling software, and the parametric plug-in Grasshopper, HPF explored placement possibilities and resultant topographic diversity based on the material's estimated angle of repose.
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Monitoring

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.

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Sean Burkholder
seanburk@design.upenn.edu
Brian Davis
mudlands@virgina.edu
Tess Ruswick
truswick@design.upenn.edu

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