II, LABORATORY OBSERVATIONS 



1. Summary of Data . 



There have been few general laboratory studies of longshore currents and 

 near shore circulations. The 12 reviewed during this study are tabulated in 

 Appendix B. Monochromatic waves were used in all cases. A maximum long- 

 shore current of 0.7 meter per second was observed, and wave heights ranged 

 up to 14 centimeters, with periods generally between 0.7 and 3 seconds. 

 For space reasons, beach slopes were larger than in nature and about 0.1 

 for most tests. A wide range of wave approach angles was tested. 



The major studies before 1967 (Putnam, Munk, and Traylor, 1949; 

 Saville, 1950^; Brebner and Kamphuis, 1963; Galvin and Eagleson, 1965) 

 were thoroughly reviewed and discussed by Galvin (1967). They continue to 

 be used today to validate analytical theories and numerical models (e.g., 

 Ostendorf and Madsen, 1979) . - 



Krumbein's (1944) study on a movable bed used a 30° beach slope and 

 was mainly concerned with sediment transport. Data from it are not useful 

 for relating to natural beach conditions. Saville 's (1950) data, although 

 for a 1 on 10 slope, are also of limited value. Circulations in the vicinity 

 of a coastal jetty were determined by Shimano, Hom-ma, and Horikawa (1958), 

 but details were lacking as to how the velocities were measured. 



Three studies (Putnam, Munk, and Traylor, 1949; Brebner and Kamphuis, 

 1963; Galvin and Eagleson, 1965) measured longshore currents induced by 

 essentially two-dimensional, horizontally propagating, monochromatic water 

 waves breaking on plane stationary, impermeable fixed-bed laboratory beaches 

 set in basins with constant approach depths. Velocities in the surf zone 

 were measured by the traveltime on dye patches, immiscible fluids, or wooden 

 floats. Surface floats were found to move 1 to 10 percent faster than dye 

 patches (midpoint), as measured by Galvin and Eagleson (1965). These 

 researchers also used a miniature current meter (5/8-inch diameter) to 

 measure velocity profiles across the surf zone and along the beach. 

 Unfortunately, in some cases, the instantaneous water depth was less than the 

 diameter of the meter propeller. The wave tank conditions were steady in 

 time, so that it was tacitly assumed in all these studies that longshore 

 currents were independent of averaging times (traveltimes) . As Galvin (1967) 

 pointed out, velocities were measured at approximately the same (midpoint) 

 position on the beach, thus reducing the influence of nonuniformity along 

 the beach due to the end-wall effects; however, a spatial mean longshore 

 current was never defined. Brebner and Kamphuis (1963) measured dye travel 

 just inside the breaker line and called this the maximum longshore current. 



For some unknown reason, it was more than 10 years before the next mean- 

 ingful laboratory investigation took place. Perhaps Galvin' s concern with the 

 nonuniformity in profiles along the beach for closed basins and the subse- 

 quent theory of longshore currents profile for infinite beaches made 



^SAVILLE, T., "Model Study of Sand Transport Along on Infinitely Long 

 Straight Beach," Transactions American Geophysical Union, Vol. 31, 1950, 

 pp. 555-565 (not in bibliography). 



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