Section III. FIELD TESTS 



1. General Program Design 



Field tests conducted during September-October 1968 were de- 

 signed to determine zones of maximum sediment movement (velocity) on 

 a real beach; improve all aspects of the RIST operation over previous 

 studies; test the modified instrumentation and new hardware; compare 

 relative merits of utilizing sand tagged with either xenon- 133 or 

 gold 198-199; and for the first time known to the author, attempt to 

 simultaneously trace sediment movement on the beach face, and in the 

 inshore and offshore zones . 



The beach near Surf, California, on Vandenberg Air Force Base 

 property, was selected for the test site (Figure 8) . It is a relatively 

 straight,, sandy beach, and the nearshore bottom is sandy to +30 feet 

 mean lower low water and beyond (Figure 9) . To accomplish the several 

 objectives, replicate experiments were designed using the two isotopes. 

 In each instance, the packets of isotopically labeled sand were dropped 

 at 5-meter intervals along a line extending from the foreshore into the 

 nearshore zone. Actual length of the injection line varied somewhat; 

 this is explained later in this section. 



As a backup to instrumental sensors, and wave-weather forecasts, 

 visual observation of littoral environmental factors were obtained using 

 the methods described by Berg (1968) and Szuwalski (1970) . These ob- 

 servations, made at least twice daily, provided data on wind speed and 

 direction, tide, wave and breaker characteristics, littoral current and 

 beach slope. As a consequence of instrument sensor failures, dependence 

 had to be placed on the visual observations and the wave and weather 

 forecasts . 



Radiation measurements are made continuously as the mobile detector 

 system is towed along the beach, through the surf zone, or along the off- 

 shore bottom. Position of the LARC XV is determined directly by the 

 Cubic Autotape navigation system used; position of the radiation detec- 

 tion vehicle is computed. The schematic diagram (Figure 10) illustrates 

 a typical RIST survey, based upon the actual experimental operations at 

 Surf. Data and placement of injection and isotope activity are summa- 

 rized in Table I. 



2. Xenon Experiments 



On 25 September 1968, 36 1-liter packets of xenonated sand 

 (specific activity 42.3 microcuries) were placed as a simulated line 

 injection 590 feet (180 meters) long from +6 feet mean lower low water 

 to -6 feet mean lower low water. The approximate position of the 

 injection along the range is shown on Figure 11 which represents con- 

 ditions immediately following injection. Several surveys a day were 



IS 



