dynamics are a complicated puzzle of interacting elements 

 — winds, waves, currents, sand and geologic formations. 

 The way these elements fit together determines how a beach 

 responds during a hurricane as well as how it recovers after 

 the storm has passed. 



Sand constantly moves along the shore. Waves deliver 

 sand and take it away. During fair weather, waves pick up 

 offshore sand and carry it to the beach via low-intensity 

 waves. That's why the beach is wider in the summer. 

 During storms, high-intensity waves eat away the sand, 

 carrying it offshore. 



Along North Carolina's coast, more sand is taken than 

 returned, so Tar Heel beaches experience an average 

 erosion rate of 2 to 3 feet per year. Some areas lose less 

 sand; others lose more. 



Sand is also transported along the surf zone via 

 longshore currents. These currents move parallel to the 

 shoreline and carry suspended sand churned by wave action 

 back and forth along the beach. 



Wind transports fine grains of dry beach sand above 

 the waterline. If halted by vegetation, sand fences or other 

 obstructions, these grains pile up to build dunes. 



Dunes act as reservoirs of sand that help to ward off 

 waves and surges during hurricanes and other major storms, 

 but they're not much help against the more gradual process 

 of erosion, says Spencer Rogers, Sea Grant's coastal 

 erosion and construction specialist. 



When it comes to storms, the more sand between you 

 and the ocean, the better, Rogers says. But for some 

 beaches, sand is in short supply. That's the case along many 

 southern coastal beaches, including Topsail, Kure and south 

 Onslow beaches. 



In fact, geologists say North Carolina beaches are sand- 

 starved. Coastal rivers deliver little, if any, sand and 

 sediment to the shoreline. 



The sand that does coat our beaches has come from the 

 gradual erosion of rocks and sediments along the inner 

 continental shelf during the last several thousand years of 

 sea level rise. But with little input of new sand, the system 

 simply continues to shuffle the same sand back and forth 

 between the beach and the nearshore continental shelf. 



When high-energy storms move ashore, their waves 

 can quickly scour away the thin coating of beach sand, 

 moving on to gnaw at the dunes. Often, the rock or mud 

 base of the beach is exposed during and immediately after 

 the storm. 



This year, North Carolina's southern beaches got a 

 one-two punch with two hurricanes slamming ashore in as 

 many months. In July, Bertha came calling, eating away the 

 berm and taking a bite out of the dunes. Large quantities of 

 sand were moved offshore. In the aftermath, the gentle 

 summer waves were restoring sand to the beach just as the 

 bigger, more powerful Fran whirled in. 



With less sand on the beach, the storm waves and surge 



4 JANUARY/FEBRUARY 1997 



