same shallow zone are referred to as offshore nourishment projects. The antic- 

 ipated benefits and most of the subsequent profile monitoring for those projects; 

 involve the beach and inner nearshore zone. In this study, as a consequence of 

 shallow-water placement during high tide and seaward migration of the low tide 

 breakpoint, some material was actually located in the surf zone, or, in the un- 

 equivocal nearshore zone. 



3. Background on Sediment Movement . 



The concept of offshore placement of dredged sediment as a means of beach 

 nourishment is based on the likelihood of net shoreward transport of the placed 

 sand. This section provides the rationale upon which the concept for shallow- 

 water placement is based. Knowledge of how wave and wind conditions affect 

 transport direction and rate is not only important to establishing the general 

 concept, but also important for determining some criteria for the placement (time 

 and location) of sediment and determining the optimum conditions for onshore 

 transport following placement. 



Wave mass transport and transport power are factors which provide a theo- 

 retical basis for the concept that net sediment transport should occur in the 

 direction of unbroken shoaling waves. A net mass (fluid) transport, although 

 small, is induced in the direction of wave movement due to viscosity (Sleath, 

 1974) as well as due to the fact that the trajectories of fluid particles under 

 finite -amplitude waves are not closed (Dalrymple, 1976) . Mass transport due to 

 nonclosure of the water particle orbit would increase as waves shoal . In addi- 

 tion, the amount of sediment transport is directly related to fluid power ex- 

 pended on the bed (Bagnold, 1963). Since fluid power is directly related to 

 velocity cubed (or higher exponents) (Madsen and Grant, 1976; Komar 1976b, 

 p. 113) sand transport should be greater during the higher velocity landward 

 flow associated with passage of the wave crest than the lower velocity seaward 

 flow associated with the wave trough. 



Although evidence supports sediment transport in the direction of wave ad- 

 vance, it is generally accepted that the added presence of an unidirectional 

 current (e.g., wind-driven current or tidal current) can alter the direction of 

 net transport, or produce a net transport where wave transport is oscillatory 

 (Bagnold, 1963; Komar, 1976a, p. 299). Cook and Gorsline (1972) reported that 

 in southern California bottom-drift direction was associated with wind-shear 

 effects as well as swell characteristics. They suggested that onshore breezes 

 caused compensatory offshore flow at depth and that offshore breezes aided 

 shoreward bottom flow. Seaward bottom drift was associated with onshore winds 

 and short -period waves; long -period swells were associated with shoreward drift. 

 Cook and Gorsline concluded that the conventional concept of wave drift was in- 

 adequate in that net offshore water transport was frequent. King and Williams 

 (1949) conducted wave tank experiments superimposing onshore winds of 13 centi- 

 meters per second. They found that the landward movement due to wave action 

 alone was converted to a slight seaward transport. 



In spite of evidence of reversals of bottom-drift direction with certain wind 

 and wave conditions, or depending upon the superposition of unidirectional cur- 

 rents, field studies utilizing sand tracers placed outside the breaker zone show 

 a predominance of onshore transport. Vernon (1965) showed that tracer grains 

 dispersed landward and more rapidly at shallower depths than in deeper water, and 

 that fine sand underwent greater movement than coarse sand. Similar findings 



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