. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 35° !5' I 10' SELECTED CONTOURS IN FEET, I 1 I Figure 6. Mean Inman <j) grain-size map based on analysis of the sand fraction. Sample locations are shown for a sample net including 1970 samples and samples from niiiip Sears taken from R/V Eastward, 1971. of a fourth order of transverse bed form in the fact that large dunes tend to occur in distina sets of two to four dunes per set (Fig. 13A). In the bathymetric map of Fig- ure 14A, two dune sets
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 35° !5' I 10' SELECTED CONTOURS IN FEET, I 1 I Figure 6. Mean Inman <j) grain-size map based on analysis of the sand fraction. Sample locations are shown for a sample net including 1970 samples and samples from niiiip Sears taken from R/V Eastward, 1971. of a fourth order of transverse bed form in the fact that large dunes tend to occur in distina sets of two to four dunes per set (Fig. 13A). In the bathymetric map of Fig- ure 14A, two dune sets are shown as single ridges, perturbing the outline of Light Tower Ridge as defined by the 18-m (60-ft) contour. Significance of Transverse Bed Forms. Allen (1968, p. 68) suggested that the fea- tures we describe as ripples are the conse- quence of transverse flow penurbations within the logarithmic boundary layer, whereas the large sand waves are responses to transverse perturbations of much or all of the entire flow. McCave (1971) observed smaller sand waves (our megaripples) climbing the backs of larger sand waves (our dunes) in the tidal sand-wave field of the Dutch coast. He cited Kennedy's (1969) interpretation fo the dual pattern, wherein the megaripples are primarily responses to bed-load transport characterized by rela- tively short particle trajeaories, whereas the dunes are the response of the substrate to suspensive sand transport and have longer particle trajectories. This explana- tion is in harmony with our observation of differing sizes of megaripples on the upcur- rent and lee sides of the dunes. The dunes, composed of finer sand carried mainly in suspension from the upstream dune, would develop small megaripples on their backs in response to the increase in bottom shear. ).o m M Figure 7. Photographs taken from the RA' Eastward, 1973. A. 1 ypical ripples within sand-wave field. Ripples are about 60 cm long and 10 cm high. B. Small ripples superimposed on l
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