Processes of Sand Transport in the Inner Margins of the Continental Shelf: ABSTRACT

Abstract

End_Page 341------------------------------During the past three years, the senior author and his students have been studying processes of sand transport in the surf zone, inner shelf, and submarine canyons along the eastern Gulf of Mexico and the Pacific Coast. Methods have included the use of fluorescent dyed sand, dynamometers, rapid beach profiling, SCUBA equipment, and time-lapse photographic apparatus. Transport phenomena have been investigated to depths of 30 meters. It is evident that sands move in the surf zone in response to the distribution of kinetic energy and are channelized between the breaker line and the swash line by energy minima. These minima and intervening maxima are exactly matched by textural characteristics of the surficial sediments. The uniform average textures of all surf zone sediments are a reflection of the presence of a compensating system that produces a narrow range of drift velocities in spite of the large range of wave heights and transported water volumes. Bigger waves break farther from shore and move water through larger cross sections. Thus the velocities tend to be roughly the same as those generated by smaller waves. The absolute quantity of sand moved, however, is very much a function of breaker size as is evide ced by profiles of beaches from different energy regimes. Surf zone water motion is complex and multi-layered. Undertows are strong and periodically flow beneath the surface water flow. Offshore, beyond the breakers, sediments move in ripples, in directions that are determined by bottom wave velocity and sediment size. Sediments of different size grades move in different directions in any individual wave condition. Inman's model of sand motion is documented. In some areas the ripple crest positions are essentially fixed while sand motion is going on, much after the fashion of standing waves. End_of_Article - Last_Page 342------------