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The Aft Deck 



Nor'easter Offers A 

 Lesson In Science 



Coastal processes are part of eveiy 

 wave and tidal cycle. But when a big 

 northeaster howls throughout the Atlantic, 

 the changes speed up. 



The late October and early November 

 series of storms that pummeled the Outer 

 Banks fascinated students of weather. Sea 

 Grant's coastal engineer Spencer Rogers 

 says the timing of the waves made the 

 Halloween northeaster unique. 



A Bulletin Board 



allows it to be moved about. 



Long waves transport sand from the 

 beachface to the dune line instead of to 

 the offshore bar. This means there is loss 

 of sand on the beach where you walk (the 

 foreshore or beachface) back to the base 

 of the dunes. The result is fatter dunes. 



The back of the beach gained more 

 sand, so the dunes appeared to be less tall. 



"Because the beach elevation is so 

 misleadingly high, things aren't as bad as 

 they might seem in many of the 



The period of the wave or the time 

 between two crests passing the same point 

 was longer than usual — 21 seconds, as 

 opposed to the eight seconds typical of a 

 local storm and the 10 to 15 seconds for 

 the average northeaster. This indicated that 

 the length of the waves was longer. 



Wave length is indicative of how 

 deep the wave action penetrates the water 

 column, says Sea Grant marine education 

 specialist Lundie Spence. A wave causes 

 water to move in an orbital fashion to a 

 depth of one half the wave length. Thus a 

 longer wave affects the bottom sediment 

 sooner and over more distance. This 

 mobilizes more nearshore sediment and 



locations," says Rogers. "There's actually 

 more storm protection in place than is 

 obvious to the layman." 



When a second storm hit a few weeks 

 after the Halloween northeaster, the waves 

 hit a more fonnidable dune line in many 

 areas. 



Moving the sand from the beach to 

 the dune line steepens the angle of the 

 beach. The flat summer beach is now 

 sloped. If you get to the coast, says 

 Spence, look for the difference. 



In some cases, waves breached 

 dunes, transporting sand to the roads 

 behind. This is the overwash process in 

 action. The second storm had less energy 



of Updates and Events 



than the first, but with high tides, it had no 

 trouble moving through the breached 

 dunes. 



The Halloween northeaster caused 

 damage to more than 500 homes and 

 businesses. 



A Double Standard 

 For Treated Wood 



If you're planning to buy treated 

 lumber to build a bulkhead or dock in salt 

 water, remember that looks can be 

 deceiving. 



The familiar green color of wood 

 treated with chromated copper arsenate 

 doesn't mean your structure will be safe 

 from shipworms. Saltwater structures won't 

 repel pesky marine borers unless the 

 lumber they're made of has been treated 

 with the proper chemical strength — 

 usually 2 1/2 pounds of CCA per cubic 

 foot, says Sea Grant coastal engineer 

 Spencer Rogers. 



"It may all look green, but if it's not 

 treated at that level it won't work," he 

 says. 



However, where wood is used for 

 decking or in areas farther inland (for 

 fence poles or house pilings), lower levels 

 of CCA treatment are acceptable, says 

 Rogers. 



If you choose to use cut lumber or 

 boards, it's also important to know 

 whether you're buying sapwood or 

 heartwood, says Rogers. The CCA 

 chemical can't penetrate heartwood, so 

 marine borers can munch right through 

 areas where heartwood is exposed. (If you 

 use round pilings, the treated sapwood 

 covers and protects the heart.) 



The Southern Pine Inspection Bureau 

 recently developed standards for treated 

 wood, and in limited areas, inspected and 

 labeled lumber is available for purchase, 

 says Rogers. 



"Seawall" grade lumber is comprised 

 of heartwood on only one side. This grade 

 is intended for bulkhead sheathing, 

 because the vulnerable heartwood can be 



18 JANUARY/FEBRUARY 1992 



