2. Current Data . 



Several techniques for measuring wave-generated currents were tried 

 in 1972 before a satisfactory technique was developed. A neutrally buoy- 

 ant liquid was considered, but the liquid lacked cohesion and a color tO' 

 make it distinctly visible in the water. Painted bits of Styrofoam proved 

 too easily affected by wind. Finally, polyethylene tubing of 5/16-inch 

 diameter (0.79 centimeter) was cut into 0.5-inch-long (1.27 centimeters) 

 cylinders (bobs) and filled with clay just to the point of floating. The 

 bobs were painted red and were large enough to be easily seen in the water ^ 

 yet light and small enough to move with the currents. More clay was added 

 to other bobs so that they were suspended near the bottom. 



For the surface currents, the path and traveltime of each bob were 

 recorded on a grid chart of the tank. Bottom currents were measured by 

 recording the position and time of observation in tabular form over 

 extended periods of time (examples in App. A). 



Fluorescein dye was used for obtaining qualitative data on current 

 patterns. 



Interpretation of the current data was difficult, unless a distinct 

 pattern was observed. In general, if a pattern of movement was observed, 

 the reduction procedure consisted mainly of determining the velocity and 

 changes in the circulation pattern. 



XI. SUMMARY 



Tliis report is a detailed record of procedures for running a series 

 of movable-bed coastal engineering experiments. Special attention has 

 been given to recording those procedures which are usually transmitted 

 informally, outside the written record, or rediscovered from hard experi- 

 ence. The report serves four general uses: 



(a) It is a procedural manual for running coastal engineer- 

 ing movable-bed experiments; 



(b) describes equipment that has been used since 1953 in 

 many experimental studies published by BEB and CERC; 



(c) explains procedures used in the 10 LEBS experiments 

 (reported separately); and 



(d) gives a detailed record of LEBS experimental condi- 

 tions for possible future re-analysis involving presently 

 unrecognized parameters. 



The 10 LEBS experiments were conducted in 6- and 10-foot -wide outdoor 

 wave tanks during testing seasons from April to December, to relate wave 

 height variability to wave reflection from a changing movable-bed profile. 



45 



