producing higher transport rates, than would be expected for the observed 

 breaker heights and angles. 



The conditions necessary to produce wind-driven currents were observed to 

 occur rather frequently throughout the study period. Based on the dye study on 

 21 July, it is reasonable to assume that the wind-driven current extended land- 

 ward into the surf zone (Fig. 4). Moreover, a shore-parallel wind-driven current 

 was measured to extend downward near the bed of the nearshore zone (Fig. 12). 

 Thus, these currents are judged not to be simply a surface current. 



In general, a superimposed net flow of any speed, e.g., a few centimeters 

 per second, is sufficient to cause net displacement of a sand grain already en- 

 trained by orbital currents. Therefore, the measured current would definitely 

 have been capable of moving wave-entrained sediment shore parallel throughout 

 the nearshore zone. When the velocity exceeded 20 centimeters per second, sedi- 

 ment may have been entrained by the wind-driven current alone. 



Inspite of the capability of wind-driven currents to move sand, the profile 

 data of this study are not suitable for examining shape and volume change in 

 relation. to known periods of wind-driven current activity. Nonetheless, wind- 

 driven currents were probably instrumental in moving larger-than-expected amounts 

 of sediment in a shore-parallel direction both in the surf zone and in the ad- 

 jacent offshore zone. 



6. Overall Transport Pattern and Rate. 



The predominant transport pattern for the disposal sediment was movement on- 

 shore, into the inshore and beach zones, then alongshore. This pattern is in 

 accord with field-measured dispersal patterns for fine- to medium-grained radio- 

 active sand tracers placed in the California nearshore zone (Duane, 1976; 

 Schwartz, 1976, 1980 in preparation] as well as with dispersal patterns for 

 fluorescent tracer studies (Ingle, 1966) . The radioactive tracer tests showed 

 that sediment which entered the inshore zone tended to remain in that zone un- 

 less moved seaward by rip current (Schwartz, 1976). 



This general pattern is also in accord with laboratory studies in which sand 

 was placed in shallow water just seaward of the surf zone (Kamphuis and Bridgemanj 

 1975) . The wave tank study by Kamphuis and Bridgeman (1975) showed that placefl 

 sediment moved shoreward and accreted to the lower beach and inshore zone in 

 response to simulated summer wave (minor storm) conditions. More recently, a 

 similar nourishment study conducted in a wave basin by Kamphuis and Readshaw 

 (J.W. Kamphuis, personal communication, 1978) showed the major difference in the 

 processes for the two- and three-dimensional settings was the generation of a 

 longshore current in the wave basin. Under similar sediment placement and wave 

 conditions, the sediment again moved shoreward, but once in the region of long- 

 shore currents, transport became dominantly shore parallel. This resulted in 

 beach accretion downcoast from the fill location rather than directly onshore. 

 Although similar accretion has not been documented for this study, the comparison 

 of field studies and laboratory studies provides evidence for onshore transport 

 into the littoral zone where longshore transport then becomes dominant. Thus, 

 sediment may be supplied to the surf zone at a relatively high rate and also 

 moved alongshore at a high rate. 



Six days following final disposal, 40 percent of the placed 26,750 cubic 

 meters of sediment had been removed from the offshore zone, 55 percent removed 



39 



