in the field to measure water surface variations, bottom pressures, winds, 

 etc., but were felt outside the intended scope of this review (e.g., see 

 Horikawa, 1978a; Gable, 1979). An additional method to develop steady 

 uniform profile longshore currents in the laboratory is also discussed. 



1 . Velocity Instruments . 



The section relies primarily on the published literature of researchers 

 making field measurements in the surf zone; useful information was also 

 obtained from Teleki, Musialowski, and Prins (1976) and Woodward, Mooers, 

 and Jensen (1978). The most recent source is the ongoing. Near shore Sediment 

 Transport Study (NSTS) and publications from it (e.g.. Gable, 1979). 



a. Lagrangian . Before 1968, currents were measured by timing the 

 travel distance of dye, surface floats, or drogues. The main advantage 

 is the simplicity of use. A mean current is obtained representative of 

 the distance and traveltime used in the measurement. Most early researchers 

 fail to mention these values in their publications. Surface floats give 

 surface readings. Dye and drogues (weighted floats) give some type of 

 depth-averaged value. The primary advantage of these methods is that when a 

 series of photos are taken from overhead, nearshore circulation patterns, 

 rip currents, and mean velocities (magnitude and direction) can be obtained. 

 Such measurement systems are described in further detail below. 



The Japanese (Horikawa and Sasaki, 1972; Sasaki, 1977) have continued 

 the use of drogues as part of their tethered float technique (Sasaki, 

 Igarashi, and Harikai, 1980). They began with polyurethane foam boxes 

 (33 by 25 centimeters) as floats and evolved to the 20-centimeter cube 

 drogue (Fig. 15). This size was found to be a minimum for viewing on ordin- 

 ary color photographic film at 200- to 500-meter altitudes. Surf boarding 

 can be a major problem with the drogue configuration when large spilling 

 breakers are present (Sasaki, 1977). Larger and heavier drogues can be 

 used but are not as readily nor swiftly deployed. Thus current magnitudes 

 and directions are very questionable in the breakers but assumed to give 

 reasonable estimates of depth-averaged longshore velocities and rip flows 

 at other locations (Sasaki, 1977). 



Dye also continues to be used. Breaking waves travel rapidly across 

 the surf zone to quickly disperse a spot of dye in the onshore-offshore 

 direction until it extends completely across the surf zone. The less 

 intense longshore diffusion then spreads the patch laterally as it moves 

 with the longshore currents (Bowen- and Inman, 1974) . What group of dyed 

 water particles are used to measure longshore currents? Most researchers 

 simply state that movement of the resulting dye-patch was measured and 

 timed from shore. Clearly, the location of the dye-patch center or 

 centroid is somewhat subjective and leads to errors. At what depth and 

 when in the wave cycle the dye is released are also important factors. 

 Laboratory researchers at the Delft Technical University (Visser, 1980) 

 released the dye at three depths (repeated twice in middle) to obtain a 

 depth-averaged value. They also released the dye at different phases in 

 the wave cycle and made 20 independent measurements to arrive at one mean 

 value. Such careful procedures would help to increase field accuracy 

 but can be applied only under steady-state field conditions. 



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