A 2.4-ineter i8 feet) Stillwater depth, which was just sufficient to 

 submerge the tops of the seaweed fronds CFig- 4), was used for all con- 

 ditions. Wave data were collected during runs of lO-minute durations. 

 The 10 wave conditions tested are listed in Table 1. Generally, three 

 runs were made at each wave condition so the reproducibility of con- 

 ditions and results could be checked. The length of the data runs was 

 chosen before the effectiveness of the wave absorber slope was noted. 

 Standing-wave patterns on the tank wall indicated that there was con- 

 siderable wave reflection from the absorber slope for wave periods of 

 6.2 and 8.2 seconds. The wave absorber had been designed for another 

 study which used a Stillwater depth of 4.6 meters and time restrictions 

 on the use of the tank made it impossible to modify the absorber for 

 the 2.4-meter water depth used in this study. Because of the wave re- 

 flection problem only the part of the wave record unaffected by reflec- 

 tion was used to calculate attenuation. Data runs were also made with 

 the seaweed field out of the wave tank for all wave conditions to pro- 

 vide a control for the analysis. 



III. DATA ANALYSIS AND RESULTS 



Wave records were analyzed to see if wave energy had been lost in 

 traveling through the seaweed field from the seaward to the landward 

 gage. Since two different types of wave gages were used, the data runs 

 with the seaweed out of the tank provided a method of eliminating system- 

 atic wave height measurement differences between the gages. The data 

 runs with the seaweed out of the tank also allowed the analysis to 

 eliminate inclusion of any losses of wave energy between the two gages 

 due to the tank walls and floor. Table 2 shows how the wave height 

 attenuation factor for wave condition 1 (Table 1) was computed. 



In Table 2, the wave heights from stations 522 and 442 (cols. 2 and 

 3) are the average heights of five consecutive waves. These five waves 

 were measured shortly after the generator was started for each data run 

 when the wave conditions had stabilized at the station but before re- 

 flected waves from the absorber slope had reached the gage. For sim- 

 plicity, waves in this category are referred to as well- formed waves. 

 The ratio of the landward wave height to the seaward height for the 

 seaweed-in and seaweed-out conditions is given in column 4. The paired 

 values of the seaweed-in and seaweed-out conditions (col. 4) form the 

 ratio which is the wave height attenuation factor (col. 5). There are 

 nine equally valid ways the seaweed-in condition can pair up with the 

 seaweed-out condition (col. 4); however, the average value of the wave 

 height attenuation factor for the nine pairings will be the same as the 

 average value in column 5. The average value of the wave height atten- 

 uation factor was tabulated for all wave conditions (Table 1, col. 4), 

 and is considered the best estimate of the reduction in wave height 

 caused by the seaweed field. 



A wave height attenuation factor of 1 indicates no reduction in wave 

 height for waves passing through the field due to the presence of the field. 



