. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography BED FORMS 169. FIGURE 10. (a) Lingoid ripple pattern on shelf floor off Cape Hatteras, Sorth Carolina, (b) Lingoid ripples on back oj sand ivave, straight ripples in trough, same area. ping of fields that occurs in diagrams utilizing fluid power or bed shear stress. Figure 11 shows that dunes (sand waves) occur at higher values of fluid power than do ripples by them- selves. This fact is consonant with Kennedy's suggestion that sand wave formation i
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography BED FORMS 169. FIGURE 10. (a) Lingoid ripple pattern on shelf floor off Cape Hatteras, Sorth Carolina, (b) Lingoid ripples on back oj sand ivave, straight ripples in trough, same area. ping of fields that occurs in diagrams utilizing fluid power or bed shear stress. Figure 11 shows that dunes (sand waves) occur at higher values of fluid power than do ripples by them- selves. This fact is consonant with Kennedy's suggestion that sand wave formation involves suspended load trans- port, which requires higher values of fluid power than does bed load transport. TRANSVERSE BED FORMS AND TIDAL FLOWS. Tidal flows, which reverse every 6 hours, generate transverse bed forms in a cohesionless substrate. Tidal current ripples are no different than ripples generated by unidirectional currents, except that their sense of asymmetry is reversed as the tide changes. Small sand waves (height of 1 m or less) may have their asymmetries partly or wholly re- versed by strong reversing tidal currents (Klein, 1970). Larger sand waves tend to display a time-integrated response to reversing tidal flows, maintaining an ebb or flood asymmetry in accord with the dominant flow com- ponent residual to the semidiurnal cycle. "Cat-backed" sand waves are large sand waves that have a sloping upcurrent side, a flat top, and (in profile) an â¢â ear" perched on the edge of the downcurrent slope (Van Veen, 1936). The ear is a response to the subordinate portion of the tidal cycle. Tide-formed sand waves in areas of equal ebb and flood flow are commonly symmetrical. As distance from shore increases, the tidal current is no longer reversing but rotary (Chapter 5). The advent of midtide cross flow tends to inhibit the formation of sand waves large enough to survive through the tidal cycle (McCave, 1971). Under such circumstances longi- tudinal b
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