by a number of methods. Radioactive material has been placed in holes 

 drilled in a large pebble. It has been incorporated in molten glass 

 which, when hardened, is crushed and resized (Sato, et al., 1962; and 

 Taney, 1963). Radioactive material has been plated on the surface of 

 natural sediments. (Stephens, et al., 1968.) Radioactive gas (krypton 

 85 and xenon 133) has been absorbed into quartz sand. (Chleck, et al., 

 1963; and Acree, et al., 1969.) 



In 1966, the Coastal Engineering Research Center, in cooperation 

 with the Atomic Energy Commission, initiated a multiagency program to 

 create a workable radioisotopic sand tracing (RIST) program, for use in 

 the littoral zone. (Duane and Judge, 1969.) Tagging procedures (by 

 surface plating with gold 198-199), instrumentation, field surveys and 

 data handling techniques were developed which permit collection and 

 analysis of over 12,000 bits of information per hour over a survey track 

 about 18,000 feet long. 



These recent developments in radioactive tracing permit in situ 

 observations and faster data collection over much larger areas (Duane, 

 1970) than has been possible using fluorescent or stable isotope tracers. 

 However, operational and equipment costs of radionuclide tracer programs 

 can be high. 



Accurate determination of long-term sediment transport volume is not 

 yet possible from a tracer study, but qualitative data on sediment move- 

 ment useful for engineering purposes can be obtained. 



Experience has shown that tracer tests can give information on 

 direction of movement, dispersion, shoaling sources, relative velocity 

 and movement in various areas of the littoral zone, means of natural by- 

 passing, and structure efficiency. Reasonably quantitative data on move- 

 ment or shoaling rates can be obtained for short-time intervals. It 

 should be emphasized that this type of information must be interpreted 

 with care, since the data are generally determined by short-term littoral 

 transport phenomena. However, tracer studies conducted repeatedly over 

 several years at the same location could result in estimates of longer 

 term littoral transport. 



4.83 SEDIMENT TRANSPORT CALCULATIONS 



4.831 Longshore Transport Rate . The example calculation of a sediment 

 budget in Section 4.76 is typical in that the magnitude of the longshore 

 transport rate exceeds by a considerable margin any other element in the 

 budget. For this reason, it is essential to have a good estimate of the 

 longshore transport rate in an engineering study of littoral processes. 



A complete description of the longshore transport rate requires 

 knowledge of two of the five variables 



(Q,,,Qe,,Q^,Q„,7). 



defined by Equations 4-21, 4-22, and 4-23. If any two are known, the 

 remaining three can be obtained from the three equations. 



4-152 



