Experiment Apparatus 



Instrument description 



A general configuration of the capacitance wave gauges is depicted in 

 Figure 4-1. These gauges consisted of a single loop of Teflon-insulated, 20- 

 gauge copper wire which was lightly twisted so that both ends of the wire 

 were attached to one terminal at the base of a PVC electronics housing. The 

 electronics housing was attached to a stainless steel support frame. A ground 

 wire from the electronic circuitry was then attached direcdy to this frame to 

 make ground contact with the water in the wave tank. The bottom of the 

 sensing wire loop was attached to the support frame by a non-conductive 

 rubber band. The purpose of this rubber band was to maintain a constant 

 tension in the sensing wire while keeping the sensing wire parallel to the 

 support frame at a fixed distance. 



The capacitance wave gauges were installed vertically with each gauge par- 

 tially buried in the sand as depicted in Figures 4-1 and 4-2. With this config- 

 uration, the initial zero elevation of each gauge was taken to be either: (a) the 

 still-water level if the gauge was located seaward of the still-water shoreline 

 where the sand bed was not exposed at the beginning of the run, or (b) the 

 wet sand surface if the gauge was located landward of the still-water shoreline 

 where the sand bed was exposed at the start of the run. Water surface eleva- 

 tions and wave heights were then measured relative to this initial reference 

 datum. 



Location 



The locations of the capacitance wave gauges varied for each run and are 

 listed in Table Dl in Appendix D. Gauges were usually placed on 3- or 6-ft 

 (0.91- or 1.83-m) spacings in the inner surf zone and swash zone. The 10 

 gauges were numbered from A to J at the start of the experiment. In almost 

 all tests, Gauge A was located approximately 1 ft (0.30 m) seaward of Station 

 5 at horizontal position* = 49.8 ft (15.18 m) in SUPERTANK coordinates 

 (Chapter 1) and, thus, 11 ft (3.35 m) landward of the first resistance wave 

 gauge. Starting from Gauge A and proceeding landward, Gauges B, C, D, E, 

 and F were normally located at 6-ft (1.83-m) intervals, though this spacing 

 changed frequently. Gauges G, H, I, and J were then used as "gauges of 

 opportunity," either as spare gauges or to fill in between the other gauges to 

 achieve a 2- or 3-ft (0.61- or 0.9 1-m) gauge spacing throughout the anticipat- 

 ed swash zone. As a result, gauge positioning did not follow alphabetical 

 order. 



A typical configuration of the gauges as used for the first three weeks of 

 SUPERTANK is shown in Figure 4-2. Note, however, that this configuration 

 changed frequently later in SUPERTANK, especially for the dune erosion 



Chapter 4 SUPERTANK Swash Measurements 



75 



