. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 306 COASTAL SEDIMENTATION. LAND py-^j OUTCROP [p%3 GRAVEL ? SAND I I MUD 1 2 3 KILOMETERS FIGURE 48. Hypothetical stratigraphy of a rocky coast undergoing transgression. to the berm. The high, steep waves of storms tend to strip sand from the beach and transport it out to the surf zone, and the cycle begins anew. The cycle tends to be linked to the cycle of seasons in that offshore transport dominates during the period of winter storms, while onshor
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 306 COASTAL SEDIMENTATION. LAND py-^j OUTCROP [p%3 GRAVEL ? SAND I I MUD 1 2 3 KILOMETERS FIGURE 48. Hypothetical stratigraphy of a rocky coast undergoing transgression. to the berm. The high, steep waves of storms tend to strip sand from the beach and transport it out to the surf zone, and the cycle begins anew. The cycle tends to be linked to the cycle of seasons in that offshore transport dominates during the period of winter storms, while onshore transport tends to dominate during the summer season of fair weather. The lower shoreface is a second province subject to onshore-offshore transport. The corresponding hydraulic regime is the zone of fric- tion-dominated unidirectional flow that constitutes the coastal boundary of the shelf flow field. During storms (or peak tidal flows) velocity in this zone may be more intense than in the zone of quasi-geostrophic flow further offshore. Downwelling and a seaward component of bot- tom flow may occur in this zone during some storm flows, at the same time that sand is moving seaward in the surf zone, so that sand is transported off the shore- face altogether. The interrelated behavior patterns of the zone of shoaling and breaking waves and zone of friction-domi- nated flows give rise on many coasts to a long-term cyclic pattern of advance or retreat of the coastal profile. The upper shoreface undergoes net aggradation and pro- gradation over a period of years tending toward the ideal wave-graded profile. A major storm or period of severe storms will result in large-scale seaward transport of sand, causing flattening and significant landward trans- lation of the profile. On coasts experiencing a net littoral drift surplus, fair-weather progradation is more effective than storm erosion, and the profile translates seaward and (in compensation for postglacial sea-level rise) up- w
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