bolted to the carriage structure. A pulley and winch system was used to 

 adjust the elevation of the base of the mast. 



Capacitance wave gauge. A capacitance wave gauge, used to determine 

 local free-surface displacement, utilizes the dielectric properties of water and 

 air to detect the position of the air-water interface. The gauge consisted of a 

 small PVC electronics housing, a jacketed wire sensing lead, and a d-c power 

 supply. The sensing lead was approximately 2 m in length, and was oriented 

 perpendicularly to the still-water surface. 



The capacitance wave gauge was mounted to a second sailboat mast, 

 attached vertically to the carriage in the same cross-channel plane as the OBS 

 array. The sensing lead ran parallel to the mast from its bottom, up to the 

 electronics housing, and was held in slight tension. The wave gauge could 

 also be moved vertically to compensate for changes in still-water conditions. 



Video camera. An 8-mm-format video camera was used to record the 

 waves as they passed by the OBS array and wave gauge. From this, local 

 wave form and turbulence intensity were visually documented. The camera's 

 internal clock was manually synchronized with Coordinated Universal Time to 

 facilitate comparison with sensor records. The video camera was mounted on 

 a wooden frame which extended approximately 1 m shoreward of the carriage. 

 From this position, an oblique view was obtained of all instruments deployed 

 from the carriage. 



Electromagnetic current meters. As described in Chapter 3, a stacked 

 array of four EMCMs was also mounted to the instrument carriage. The 

 gauges, which measured vertical and cross-shore velocities, were located in 

 the same cross-channel plane as the OBS and wave gauge. 



Location 



The instrument carriage was used to measure and observe sediment sus- 

 pension and associated fluid properties at any position between Stations 5 

 and 18, which spans a distance of approximately 50 m. However, the 

 majority of measurements were taken in the outer surf zone, between Stations 

 7 and 10. The bottommost OBS was typically located within 8 cm of the bed 

 and the topmost sensor nominally 35 cm from the bed. 



The capacitance wave gauge, OBS array, and EMCM array were fixed in 

 the same cross-channel plane. In this plane the wave gauge was positioned 

 along the line y = 105 cm, the OBS array was at y = 150 cm, and the 

 EMCM array was at y = 260 cm from the zero reference for the SUPER- 

 TANK coordinate system (Chapter 1). Cross-channel positions for the wave 

 gauge, the OBS array, and the EMCM array were constant for the 

 SUPERTANK project with the exception of the relocation of the EMCMs for 

 the dedicated suspended sediment test, STBO. 



Chapter 7 Sediment Suspension Measurements from a Platform 



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