of the study, 1,300 data points (collected at 2-second intervals) were 

 analyzed; and about 20,000 square feet (10,000 feet of track times a 

 2-foot width visible to detector) , or .017 of the area mapped, were 

 actually sampled. On 9 October (Figure 20), a rectangular area 3,300 

 by 1,600 feet (in excess of 5 million square feet) was surveyed in less 

 than 2 hours - 126 hours after injection of the isotope. The survey 

 extended from +6 feet on the beach to -15 feet seaward of the surf zone. 

 All told, 3,000 data points were collected over a track nearly 20,000 

 feet long. That track length represents examination of nearly 40,000 

 square feet of the area represented by the map or about 0.0075 of the 

 total area. A more significant comparison of the RIST data and that 

 of Ingle's study is illustrated on Figure 25. The paper by Courtois 

 and Monaco (1969) does not indicate the number of data points, but the 

 dimensions of the dispersing mass of sand can be determined from the 

 maps illustrated. For comparison purposes the larger pattern is also 

 illustrated on Figure 25. 



A search of literature shows no other studies have synoptical ly 

 examined the beach face, inshore zone, and the offshore bottom. Other 

 reported studies are confined to a beach face or deep water (a harbor, 

 a bay, or the ocean seaward of the surf zone) . The earlier inability to 

 look at the inshore zone, the zone of maximum transport, has been due to 

 the detection vehicles and detector systems that were not rugged enough 

 to withstand the extreme forces of the surf zone. The ball- type detector 

 developed for RIST solves this problem. However, the general technique 

 of towing the detector vehicle over the sediment-water interface where 

 sediment transport is taking place is common between the RIST system and 

 other radioisotope tracer systems. Use of a 4-detector array provides a 

 high degree of sensitivity, increases detection capability, and examines 

 a larger area, and thus improves the counting statistics. The RIST data 

 acquisition system, which automatically collects and correlates time, 

 position, and radiation counts, is unique in the field of sediment 

 tracing. 



Section V. SUMMARY 



Studies carried out at Surf, California, indicate the suitability 

 of the techniques and technology developed in the RIST program for simul- 

 taneously tracing sediment on a sand beach, through the surf zone, and to 

 the offshore bottom beyond. Sand labeled with the radioisotope of gold 

 198-199 provides much more data for analysis of sediment movement than 

 does sand labeled with xenon-133. In respect to collected data, gold is 

 considered to be superior to xenonated sand for field tracing purposes. 

 Use of a multiple-photon isotope, such as the mix gold 198-199, coupled 

 with a data collection system capable of discriminating between specific 

 spectral levels, makes it possible to determine relative depths of burial, 

 provided labeled sand is overlain by "dead" sand. 



Surveys conducted confirm that, in response to any given set of 

 wave conditions , a very different rate of sediment movement occurs in 



42 



