Most tests conducted in previous LWT projects ran waves over relatively 

 long time periods, for example, 30 to 100 hr of wave action, to approach an 

 equilibrium shape. Another departure of SUPERTANK strategy from pre- 

 vious LWT projects was use of short-duration tests to realize a wide variety of 

 wave, initial beach profile, and foreshore or landward boundary combinations, 

 instead of performing a small number of tests (perhaps four), as had been 

 done in the past, to achieve effective equilibrium. Although a greater number 

 of tests were run, many difficult decisions had to be made in prioritizing 

 objectives. It was reasoned that previous LWT tests had provided much 

 information on the approach to equilibrium profile shape and on the equili- 

 brium shape itself, and that improvement of quantitative simulation models 

 and mathematical models of the basic processes would better benefit from a 

 wide variety of conditions. Some tests were run for sufficient time to clearly 

 discern the approach to an equilibrium shape. 



Although guided by a 6-week plan of tests, modifications and refinements 

 for improving both the quality and scientific merit of the data collection were 

 made on a weekly and even daily basis as experience was gained and tradeoffs 

 were evaluated. These decisions were ultimately made by the two authors of 

 this chapter as senior representatives of CERC. The pre-planned test series 

 was modified and redirected as necessary through observation of the data and 

 discussion among investigators. All data sets could be inspected during col- 

 lection or shortly thereafter. 



Channel, equipment, and operating procedures 



The channel of the LWT at the WRL is 104 m long, 3.7 m wide, and 

 4.6 m deep, into which a 76-m-long beach was constructed for the 

 SUPERTANK project. Figure 1-1 shows the interior of the WRL enclosure 

 and computer control room, and Figure 1-2 is a view of the LWT during an 

 instrument change. The beach was composed of approximately 600 cu m of 

 sand. The direct, digital controlled servo-hydraulic wave generator was 

 equipped to absorb energy at the peak spectral frequency that was reflected 

 from the beach and structures, such as dunes and seawalls. Broad- and nar- 

 row-band random waves and monochromatic waves were run with zero- 

 moment wave heights in the range of 0.2 to 1.0 m and with peak spectral 

 periods in the range of 3 to 10 sec. As mentioned previously, waves were 

 typically run in segments of 10-, 20-, 40-, and 70-min duration. 



A coordinate system was set up at the LWT to reference all instrument 

 positions. The zero point (x, y, and z = 0) was established at the beach end 

 of the tank on the west wall (right side of the tank when standing on the beach 

 and looking toward the wave generator). The positive x axis was directed 

 offshore along the top of the wall, and the positive z axis was directed upward 

 from the top of the tank wall in a right-handed coordinate system. A system 

 of reference stations was also established along the west tank wall. Stations 

 corresponded to the location of 1-in. threaded wall inserts used for instrument 

 mounting. At each station inserts were paired horizontally (0.3-m spacing) 



Chapter 1 Introduction to SUPERTANK 



