term study, sponsored by the Army 

 Research Office, to map the seafloor in 

 the surf zone out to depths of 30 or 40 

 feet. The goal is to see how the seafloor 

 changes as storms move sand around. 



"We're very interested in what 

 happens when erosion removes all the 

 sand on a particular part of the seafloor, 

 exposing older rocks that aren't 

 erodible," Drake says. "There isn't 

 much sand on the barrier islands, 

 sometimes none, yet all the models for 

 predicting beach change assume that 

 there is an infinite supply of sand. So 

 knowing the response of the beach when 

 the sand supply disappears is very 

 important to understanding the North 

 Carolina coast." 



Duke University graduate student 

 Rebecca Beavers discovered that plenty 

 of sand is moving into the water at 40- 

 foot-depths, far deeper than sand is 

 typically thought to move. Beavers dons 

 scuba gear to extract sand samples by 

 hammering square cans of stainless steel 

 into the seafloor. With other SandyDuck 

 scientists monitoring waves, currents 

 and bottom changes between the times 

 that the cores are extracted, Beavers and 

 her colleagues can compare the sedi- 

 mentary strata or layers in the core to the 

 processes that created them. After 

 visiting the same sample sites and 

 taking a time sequence of cores over 

 several years, she sees that layers of 

 deposited sand observed in the first 

 cores are now missing. These have 

 been replaced in subsequent cores with 

 a new sequence of layers, usually sand 

 that has been deposited by storms. This 

 is clear evidence of erosion at the 

 sample sites, she concludes. 



With all the beaches in the world, 

 why choose Duck for this research? 

 Although the area is famous for its 

 recreational merits, Duck is also widely 

 recognized in the scientific community 

 as the perfect test site for wave research. 

 Bill Birkemeier, chief of the FRF and 

 principal coordinator of SandyDuck '97, 

 notes that Duck has been a focal point 

 for coastal experiments for many years. 

 Engineers and scientists at FRF have 

 gathered more than 20 years worth of 



weather and wave data to 

 support the research. 



"This is probably the 

 best-studied beach in the 

 world because we have a 

 straight beach with ocean 

 exposure and variable 

 conditions — calm to 

 stormy and everything in 

 between," Birkemeier says. 

 "And the FRF has both the 

 expertise and the special- 

 ized equipment required to 

 work in the dynamic 

 coastal zone." 



Take the CRAB, which looks as if 

 Dr. Seuss designed it in a moment of 

 oceanographic whimsy. This 35-foot-tall 

 motorized tripod was driven daily over 

 the dunes and into the ocean to map the 

 seafloor. The CRAB was also used to 

 install instruments, collect sediment 

 samples and tug instrumented sleds into 

 the surf. Regular surveys of the seafloor, 

 made with the CRAB since 1980, have 

 produced perhaps the most valuable data 

 at the FRF. These one-of-a-kind seafloor 

 maps help near-shore scientists to 

 precisely place their instruments for the 

 best research results. For example, if 

 they know from the maps where a 

 sandbar usually migrates during a big 

 storm, then they know where to place 

 instruments to best record how it moves. 

 Otherwise, the instruments might be 

 buried. They can also measure subtle 



variations in wave height and water 

 surface elevation — forces that drive 

 both longshore and rip currents. 



Driving the CRAB, which typically 

 motors along at a top speed of 2 mph, 

 can also be a first-class, white-knuckle 

 experience. Drake recalls one weekend 

 when graduate student Peter Dickson, 

 one of three CRAB drivers, headed into 

 the surf zone during a nor'easter. It was 

 the kind of day you'd watch seagulls fly 

 backward in the wind, he says. Winds 

 were up to 40 mph, waves occasionally 

 reached 10 feet and the longshore 

 current ripped past. The CRAB, slapped 

 by one of these storm waves, took a 4- 

 foot sidestep and almost entangled in a 

 picket fence of pipes that hold instru- 

 ments. 



The CRAB driver uses a computer 

 navigation system much more accurate 



24 WINTER 1998 



