Abstract

A technique was sought which would be a simple, useful means for determining sediment dispersion in shallow, high energy marine environments. The one chosen was based on changes in textural properties with changes in energy. In order to test this technique, grab samples were collected from the Northern Channel Island Passages off the Southern California Coast. The four textural moments were calculated for each sample and polynomial trend surface contour maps were constructed for mean and sorting for each passage. San Miguel Passage is characterized by sediment dispersion to the southeast. The energy level is highest in the center of the passage and there is a gradual decrease in energy toward the perimeter. Santa Cruz Channel is more complex. A lobe of coarse sediment, part of which appears to be relict, in the northern section of the channel shows dispersion to the east. However, finer sediment is moving into the southern part of the area from the east, where it is intercepted by the head of Santa Cruz Canyon. Because there is movement to the east and west, this channel may represent a shear zone between two currents. Anacapa Passage shows dominant westward dispersion along both the southern and northern margins, with the southern one being the most significant. Relict sediment appears to exist in this passage as well. Wind-driven currents are more important than either tidal currents or wave action in accounting for sediment distribution. Although the latter two are continually active in the passages, it is believed that their effect is superimposed on the net movement caused by wind-driven currents and hence are subordinate processes. Independent current measurements in the passages supported these interpretations.

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