for a short distance seaward of the breaker zone (Taney, 1963). In a 

 2-dimensional sense, several aspects of that model are analogous to the 

 field data. Core data, obtained at Surf, California, indicate far 

 deeper burial (maximum 1.2 feet) than the 0.10 foot reported for the 

 model, although it is not possible to make a scale comparison. 



Little onshore-offshore movement was indicated during the field 

 test. Some onshore movement of the first injection of gold-tagged sand 

 is indicated in Figures 16, 17, and 18. However, after the second in- 

 jection, shoreward movement of the offshore sand was obscured by the 

 very rapid alongshore movement of the sand from the second injection. 

 The survey made on 9 October indicates some seaward movement of tagged 

 sand; high waves during 6, 7, and 8 October are judged the cause. Using 

 fluorescent grains, Ingle (1966, page 189) found ". . . .in all cases, 

 the majority of tracer grains traveled shoreward into the breaker zone 

 although dispersion occurred in all directions". However, in Ingle's 

 study of sediment movement immediately seaward of the breaker zone, sand 

 was released 75 feet seaward of the breaker zone. During the RIST test, 

 tagged sand was released along a line extending up to 350 feet beyond 

 the breaker zone. Later, however, as a result of a storm and subsequent 

 high waves on 7 October, the most seaward release point was in the breaker 

 zone. By analogy then, the tagged sand should have been moved shoreward 

 to the beach. The data do not show that this occurred. 



Downcoast (lateral) movement is very evident, and during the initial 

 surveys some slight upcoast movement of sand is evident, particularly on 

 the beach face. However, rather sharp upcoast truncation of tagged sand 

 is on all maps; it was not expected, but has been found in other RIST 

 tests in nearshore areas. Such patterns appear to preclude the use of 

 simple diffusion models to explain the dispersal of tagged grains. 



Another point of interest is the location of zones of transport 

 relative to the breaker zone. All maps depicted indicate the zone of 

 breaking waves during the time of survey. Because of the tide and wave 

 conditions, the seaward limit of breakers was at about -5 feet mean lower 

 low water for the first survey of 5 October (Figure 18) , and at about 

 -6 feet from then to 7 October when the limit moved to about -12 feet. 

 Movement of sand seems to be restricted to the zone of peaking, breaking 

 and trans latory waves. 



Data also reveal zonal differences in relative rate of longshore 

 movement. Survey data on 5 October (Figures 19 and 20) show that sediment 

 at the landward margin of the breaker zone moved alongshore in about 3 

 hours the same, or greater, distance than that sediment seaward of that 

 zone moved in 26 hours. Sediment on the beach face moved slower than 

 sediment in the inshore zone, but faster than that in the offshore zone 

 (seaward of the surf zone) . Survey data on 9 October (Figure 21) indi- 

 cate that much of the tagged sediment previously present in the inshore 

 zone had moved completely out of the survey area. Ratios of count rate 



34 



