BY ROB YOUNG
There seems to be quite a bit of excitement these days about the potential for so-called "wave dissipation devices." An experimental one was deployed along the shoreline of the Isle of Palms, and the South Carolina Legislature is considering adding language to a bill that would specifically define these devices and add them to the arsenal of coastal protection tools to be deployed along the coast. The nation's shorelines are eroding, and there have been many attempts over the years to find the silver bullet - a device that will halt erosion, protect property and cause no downdrift harm to neighboring homes or the environment. Many such devices have been proposed over the years, and none of them has panned out.
We must approach our consideration of these proposed remedies cautiously before we label them useful and before the Legislature indirectly endorses it by inclusion in any coastal management legislation. At the moment, the state of South Carolina has stringent permitting requirements for coastal protection methods that we know work, like beach nourishment. It certainly makes sense that new, relatively untested devices should face at least the same requirements.
I have reviewed the document evaluating the installation of the wave dissipation device on the Isle of Palms. Let me tell you what the report does not evaluate.
It does not examine the downdrift impacts resulting from any accumulation of sand. The report indicates that the device accumulated sand during its installation. If this is the case, that sand was removed from the longshore transport system depriving downdrift areas of that sand. A longer installation might then accumulate significant amounts of sand creating a significant downdrift deficit of sand. One of the reasons that many states (including South Carolina) ban seawalls and regulate groins is because of the downdrift impacts that can result from interfering with the longshore transport system.
The device has not undergone rigorous engineering design or testing. What force can the pilings withstand before they lean? What precise level of protection will it provide? Under what storm and wave conditions is it likely to fail? Traditional seawalls can create significant "end effects" during storms where neighboring properties see increased rates of erosion, shoreline retreat and storm damage. Could the same happen at the ends of a longer installation of this device? There has been inadequate testing thus far to answer any of these questions.
The setting in which the device was tested does not represent much of the South Carolina Coast. The device was tested along a stretch of shoreline currently undergoing rapid change, shoreline translation, and beach profile deflation. Separating out any negative impacts of the structure from the current dynamics along the Dewees Inlet shoreline of the Isle of Palms is problematic. If the device is even to be considered for statewide installation, it should first be rigorously, objectively tested in multiple geomorphic settings.
It appears as though the device requires a piling to be installed every 10 feet and they appear to be around one foot wide. This means that, even if the crossbars are removed, the device will be blocking 10 perecent of the beach. The impacts of this should require further environmental evaluation.
I understand the desire folks have to protect coastal investments and infrastructure. I also understand that the state has an interest in leaving the door open for new coastal protection technologies. But, those new technologies need to withstand the same level of scrutiny as the tried and true methods, if not more. Legislation under consideration in the South Carolina Senate would allow a simple, non-peer reviewed study from a state educational institution to certify that a device "qualifies" to be used for emergency coastal protection. It doesn't even require that the individual completing the study have any particular expertise in coastal processes.
Before we get everyone's hopes up by writing a particular technology into law, it seems prudent that we know the implications inside and out. We don't want folks to waste their money. We don't want to cause harm to neighboring properties. And we do not want to have unintended impacts on the state's critical areas.
The South Carolina Shoreline Change Advisory Committee in 2010 recommended the establishment of a technical advisory committee that could tackle the professional evaluation of devices like this along with all other coastal protection measures to ensure that citizens are able to make the best decisions possible. Perhaps instead of endorsing a particular new device, we should consider developing a solid methodology for reviewing these activities in the future.
Rob Young is director of the Program for the Study of Developed Shorelines at Western Carolina University. He recently served on the South Carolina Blue Ribbon Committee on Shoreline Change.
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