Marine 



Advice 



Extending Knowledge to the Coastal Community 



Relief For Ailing Shores 



As long as there have been wind and waves, there's been 

 coastal erosion. But people have made the problem worse. 

 Our intensive use and mismanagement of estuarine shoreline 

 has created even more of a need to preserve its condition. 



Methods of controlling estuarine erosion — such as 

 bulkheads, groins or breakwaters — are as diverse as the 

 shoreline itself. A number of them work. Others are ineffec- 

 tive. Some are even environmentally detrimental. And all are 

 expensive. 



Sea Grant is looking at a new strategy, breakwater-marsh, 

 which actually combines two veteran erosion-control methods 

 — offshore breakwaters and planted marsh. 



"The method is combining very small wooden breakwa- 

 ters with planted marsh grasses to provide a lower cost 

 alternative," says Spencer Rogers, Sea Grant's coastal engi- 

 neer. "It's perceived as an environmental asset because it 

 turns an eroding shore into marshland." 



The Albemarle-Pamlico Estuarine Study has recently 

 provided some funding so that Rogers and selected property 

 owners can construct marsh-breakwaters as demonstration 

 models. 



"Sea Grant has been doing research in marsh grass for 

 erosion control for many years," says Rogers. Marsh grass 

 plantings alone can control erosion in some sheltered areas. 

 These usually control bank erosion for three to five years; 

 some last even longer. 



But used to control an eroding shoreline, marsh grass has 

 its limitations. In areas of moderate to high wave activity, a 

 short life is one of them. 



The grasses develop a dense bed of stems that gradually 

 dissipates waves, and form a root mat or peat layer that is 

 very dense and erosion-resistant on the surface. But the outer 

 edge of this peat layer is gradually undermined and eventu- 

 ally collapses and disappears. 



Combined with a small breakwater that protects the outer 

 edge of the marsh, grasses can be survive much longer. 



"The purpose of the breakwater is purely to prevent the 

 marsh erosion. It doesn't actually protect the upland," Rogers 

 says. "The marsh or breakwater alone would not control bank 

 erosion." 



A good test of the combination occured unintentionally in 

 the late 1970s on the Pamlico River west of Bath. The owners 

 of a church camp, struggling to deal with their eroding 

 shoreline, built an illegal wooden bulkhead. Before they 



Peat Erosion Occurs at Normal Water Levels 



Deposition 



Storm Water Level 



Peat Forms from Roots . 

 Erosion y 



Normal Water Level 



Low Breakwater 

 Protects Marsh 



Breakwater 



could backfill it, the state learned of the violation. 



After some negotiation, the state allowed the camp to 

 leave the structure in place as an offshore breakwater. A Sea 

 Grant researcher planted some grasses behind one section; 

 other grasses sprang up voluntarily. 



"This breakwater was very low — about 6 inches above 

 high water, and in water depths of 2 to 3 feet," says Rogers. 

 "A marsh very rapidly became established, and it built up a 

 good peat layer." 



After the church sold the camp, the property was subdi- 

 vided and purchased by individual owners who, unaware of 

 its significance, removed the breakwater. Within six months, 

 most of the marsh was gone; in two years it had completely 

 disappeared. The bank erosion returned. 



"Eventually all the property owners built bulkheads to 

 protect the shoreline," says Rogers. "There's no marsh or 

 beach now. And all that was needed to keep the marsh in 

 place was this very low inexpensive breakwater." 



Construction of marsh-breakwaters costs $25 to $35 per 

 foot of shoreline protected, including the cost of planting 

 marsh grass. Typical bulkhead prices range from $40 to $75 

 per foot. 



All areas aren't suited to a breakwater-marsh, Rogers says. 

 The method is most useful in areas where there's too much 

 wave activity for marsh grasses alone to work. 



To keep the cost reasonable, the offshore waters must be 

 shallow — less than 3 feet deep 50 feet offshore. 



The demonstration projects will be constructed in the 

 northeastern part of the state during the next year. 



— Carla B. Burgess 



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