cern that long-period seiching would be amplified if long wave time series 

 were used. Some seiching was recorded, and the degree of seiching depended 

 on the type of waves (monochromatic or random), and on the shoreward 

 beach configuration (a sloping beach or a seawall). Third, by stopping wave 

 action after relatively short time intervals, the elevation from the sand surface 

 to the sediment sensors could be measured for use in calculations, and these 

 and other sensors could be repositioned as necessary. Fourth, because the 

 wave gauges and current meters were sampled at 16 Hz and other instruments 

 were sampled at 10 Hz, shorter runs gave data files that were manageable in 

 size. 



The SUPERTANK wave conditions were designed to balance the need for 

 repetition of wave conditions to move the beach profile toward equilibrium 

 and development of a variety of conditions for hydrodynamic studies. The 

 TMA spectral shape, applicable to finite water depths (Bouws et al. 1985), 

 was used to design all random-wave tests, with spectral width parameter y 

 between 1 (broad-banded) and 100 (narrow-banded). Other parameters that 

 controlled the hydrodynamics, such as water level, bottom profile shape, and 

 shoreward boundary (seawall, dune, and terrace), also varied between tests, 

 changing the nearshore hydrodynamics for the same imposed offshore wave 

 conditions. 



The daily work schedule was 12 hr of wave action and associated data 

 collection activities from Monday through Thursday and 8 hr on Friday, start- 

 ing with a daily meeting of principal investigators at 7 a.m. Plans for the day 

 were reviewed and optimized at the morning meetings, and in the evenings, 

 data taken that day, particularly the beach profile change data, were inspected. 

 Evenings and weekends were spent in major mechanical operations of beach 

 profile reconstruction, emplacement and removal of dunes and seawalls, and 

 inspection and moving of instruments, for which the tank was drained. For 

 example, changes in wave conditions from higher to lower waves required 

 shoreward translation of instruments to optimize measurement coverage in the 

 vicinity of the breaker zone and in the surf zone. 



Previous LWT projects (and most small-scale laboratory experiments) on 

 beach profile change typically initiated tests from the same uniform slope, 

 which required substantial sand transfer and profile regrading with heavy 

 equipment. In the case of SUPERTANK, various researchers could be onsite 

 for only a limited time and a large number of instruments were mounted 

 inside the tank that required substantial effort to remove and re-emplace. 

 Therefore, extensive regrading of the profile, with the associated delays, was 

 not economically feasible. As a result, most tests were initiated using the 

 final profile configuration of the previous run or a modified form of it. This 

 substantial time savings was one way to obtain more data on physical process- 

 es of interest. Also, it was felt that numerical simulation modeling of profile 

 change was sufficiently advanced to start from an arbitrary profile shape, and 

 comparisons of all types of runs to a fixed initial profile were not considered 

 necessary. 



Chapter 1 Introduction to SUPERTANK 



