Re-imagining Breakwater Design to be High Functioning and Ecologically Enhanced

Abstract: The twenty-first century has heralded a new direction and vision for the coastal engineering community. The goal is no longer to simply design solutions to resist the ravages of natural forces through brute force installation of hardened surfaces, but to instead work with nature and leverage natural processes to evolve solutions that are as effective in performing the primary role of defending the coast. Such an approach can bring added value to the solution by intrinsically integrating habitat and natural forms into the design.

At Illinois Beach State Park,, the Illinois Department of Natural Resources sought to find a way to mitigate, in as natural and least intrusive means possible, the losses to the last vestiges of a rare and irreplaceable highly eco-valued shoreline. In the ideal solution, the mitigation would be unseen by park visitors. Such a solution would incorporate designs assembling submerged reefs and the limited use of major offshore structures. The latter would be ideally configured as islands and disguised as geologic formations and embody significant habitat character.

To achieve the litany of ecological as well as physical goals, we needed to develop an understanding of exactly how such atypically shaped structures influenced the incident wave field. Ultimately, the goal was to stabilize the shoreline with the minimum amount of physical intervention. If habitat enhancements degraded the breakwater performance, they would detract from the overall project goal. Alternately, if these biological additions improved performance, that would be a win-win.
Even neutral effects of these enhancements on breakwater performance needed to be proven.

Hypothetical breakwater cross sections, each embodying possible habitat enhancement features, were tested for overtopping wave transmission. In the tests, variations were examined which included the permeability of the core, the height of the core relative to the design water line, the width of a structure crest, the changes in front and rear face structure slopes, the introduction of a still basin tidal pool area in the lee of the structure, and the introduction of submerged appendages on the stoss face of the breakwater creating fish fingers and alleys.

The model test results revealed significant performance deviations from traditional overtopping transmission formulas and experience. Raising the interior breakwater core allowed significant lowering of the breakwater crest height for the same incident wave conditions. Flattening of front face slope, combined with a reduction in armor size to better achieve bio compatibility, gave limited functional benefit.

The biggest impact on reduction of wave overtopping and transmission was found by introducing fronting reef streets (fish fingers). Similar beneficial results were noted for lee side habitat ponds where perched pools of water intended as juvenile fish nurseries co-serve as stilling basins to overtopping waves.

Incorporating these new design elements into the design of a breakwater offer opportunity to improve visual aesthetics by lowering breakwater crest heights and creating breakwater geometries which better emulate natural landforms. This paper presents the results of laboratory testing defining the overtopping and transmission behavior of breakwater geometries outfitted with habitat enhancing features.

How does this project / topic contribute to the advancement of the industry and profession?: This paper offers new engineering and design guidance for building harbor infrastructure that embodies living shoreline and Engineering with Nature Principles. suggesting alternative means of using ecologically targeted design features to actually also improve the protective performance of a breakwater or shore protection. This is a reveal of newly discovered, and heretofore unpublished breakwater performance properties.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: Yes, the paper illustrates alternative ways to design a breakwater by three dimensionally altering its geometry to functionally perform equal or better than by traditional design methods yet now embody habitat enhancing components.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: Because there are no analytical or numerical methods to examine these design ideas, the understanding required extensive physical model testing to establish the performance properties.

Who is the target audience for this paper?: Coastal engineers, breakwater designers, living shoreline specialists, and fisheries ecologists/biologists.