What The Experts Say
Many coastal experts have written about the effectiveness of terminal groins and how these structures can play a valuable role in protecting beaches from erosion without significant adverse impacts.
Robert G. Dean
Professor
University of Florida
Prof. Robert Dean is considered one of the pioneers in the development of coastal engineering and has contributed to many engineering projects within the United States coastal region as well as internationally. He has specifically studied the use of terminal structures at inlets, including a 1993 study that examined six successful examples of terminal structures in Florida. Click here for a more complete bio.
Dr. Dean has shared his thoughts on terminal structures below:
My experience and position relating to terminal structures as an option available to address coastal engineering situations are summarized below. It is my understanding that the issue of whether or not terminal structures should be considered as an option in North Carolina is generic and thus the discussion below does not address any particular design nor location.
The question of whether terminal structures should be available as an option to manage inlets and beaches is linked to the manner in which such structures interact with the adjacent shorelines and this interaction is unique to the location and processes at the site, depending on the inlet and longshore sediment transport characteristics. Thus, certainly a particular terminal structure design should not be considered as a universal solution at all inlets. However, I believe that terminal structures should be available as one tool in the array of options to manage inlet/shoreline interaction. This position is based on study of many inlets in Florida and elsewhere before and after the installation of terminal structures. I have documented a portion of this study in the paper listed below. In particular, relatively short terminal structures on the updrift and downdrift sides of an inlet will prevent sand from flowing into the inlet where much of it can be lost (in flood tidal shoals) to the active beach system. My interpretation of the available data is that the terminal structure on the south side of Oregon Inlet is an example of the effectiveness of such a design in reducing erosion on Pea Island.
In summary, my position is that terminal structures should be available to coastal engineers and managers as one option to manage the interaction of sand flows at inlets with the adjacent beaches. To disallow this option definitely limits the effectiveness and costs with which related erosion problems can be addressed. Detailed studies should precede the installation of any such permanent terminal structures. To instill confidence in the process, the investigation and design of a particular terminal structure could be overseen by a group consisting of all interested parties.”
Reference: Dean, R. G. (1993) “Terminal Structures at Ends of Littoral Systems,” Journal of Coastal Research, Special Issue 18, pp. 195 – 210.
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The U.S. Army Corps of Engineers on Terminal Groins:
“Groins on the updrift side of inlets can benefit nearby beach nourishment projects by controlling (or gating) the amount entering (lost) to the inlet….Terminal groins fill quickly and do not have major impacts on ebb tidal shoals, and normal inlet, sand-passing processes.”
Source: Coastal Engineering Manual
Shore Protection Projects (V-3-73)
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Tom Jarrett, Coastal Engineer
Retired, U.S. Army Corps of Engineers
Tom Jarrett is a respected coastal engineer who spent much of his career with the U.S. Army Corps of Engineers. He now consults with coastal communities in North Carolina and nationwide.
N.C. should study use of terminal groins
“The news media often uses the worn-out phrase that hard structures ‘solve one problem while creating another somewhere else along the beach.’ While this may be so in some instances, it is by no means true in every case. The two existing terminal groin projects in North Carolina are examples where this has not occurred.”
Research indicates terminal groins can be effective
“North Carolina has successfully used terminal groins in the past and should consider the use of groins adjacent to unstabilized tidal inlets. This is where our state faces the most significant beach erosion challenges and the area where science has proven that groins can work.”
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Orrin Pilkey
James B. Duke Professor Emeritus of Geology
Duke University
Dr. Pilkey has questioned the effectiveness of using terminal groins in conjunction with beach renourishment. However, he has previously published articles which conclude that groins do increase the value of beach renourishment efforts. Below is an excerpt from a study by Pilkey and others that was published in 1990.
On the Atlantic coast, groins appear to increase the longevity of replenished beaches. Examples of this include Edisto Beach, SC, where groins have been used in conjunction with replenishment, and Virginia Key, FL, where groins were added in 1977. In both cases, the presence of the groins is believed to have increased the stability of the emplaced fill, so that some of the fill was apparently still in place more than five years after emplacement.
Similarly, the Pacific coast has repeatedly experienced general success at least partly attributable to the presence of groins. Capitola, Cabullo Beach, Redondo Beach, and Newport Beach are examples of beaches where a terminal groin has assisted in stabilizing the beach.
Source: “A Comparison of Beach Replenishment on the U.S. Atlantic, Pacific, and Gulf Coasts,” by Lynn A. Leonard, Katharine L. Dixon and Orrin H. Pilkey. Published in the Journal of Coastal Research, Special Issue 6 - Summer 1990.