Kana: There are better solutions for DeBordieu, entire coast

May 18, 2014 

Timothy Kana

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— It is disappointing that the Legislature is close to allowing homeowners at DeBordieu Colony to beef up an existing seawall and authorizing the installation of certain wave-dissipation devices. Much better erosion solutions are possible.

DeBordieu and the state would be better-served by encouraging those homeowners, at their expense, to pump sand to the beach and install sand-retaining structures — groins or breakwaters — at the downcoast end of the development.

A wave-dissipation device being tested at Isle of Palms would be expressly allowed under the legislation. It will not restore the beach and very likely will be severely damaged as soon as it is exposed to waves that come up to one’s belt buckle.

There are a few places along our coast where sand is drawn off at higher-than-normal erosion rates. DeBordieu Colony is one of those sites. Half of the two-mile stretch of beach erodes at more than 10 feet per year because an unstable spit to the south is losing sand even faster. As the spit erodes, it draws off sand from in front of the seawall and sends it a mile downcoast where it accumulates in North Inlet. In stark contrast, the northern half of DeBordieu is gaining sand and has healthy dunes.

Homeowners at DeBordieu have added sand three times since 1990 only to see it wash away quickly and leave the timber bulkhead exposed 12 feet above the low-tide line.

The beach at DeBordieu Colony would retain sand in front of the seawall if groins or breakwaters were installed near the property boundary with adjacent Baruch Foundation. Thus the present structure will not require extensive reinforcement.

One oceanfront house 25 feet behind the seawall recently sold for a fraction of the market value of properties in the healthy half of DeBordieu. Consider how all property values — and tax revenues — tend to be adversely impacted by bad news coming out of the neighborhood.

Opponents of groins worry about downcoast impacts. But in this case, the downcoast area is a wildlife preserve that has been rolling back 15 feet per year for decades. With or without groins and nourishment, this fact will not change.

If the Legislature is serious about maintaining our beaches and the tax base of coastal properties, it should be encouraging solutions like nourishment for most of the developed coast and removing barriers for sand-retaining structures in those few sites where the downcoast inlet is exacerbating erosion far more than any groin or breakwater. Unlike the likely doomed wave-dissipation device, there are proven designs for groins and breakwaters that have functioned for decades with little maintenance. Just ask the Dutch.

Tim Kana

President, Coastal Science & Engineering

Columbia

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