considerable wave reflection, causing significant changes in wave height 

 and period seaward of the breakwaters during continuous wave generation, 

 and necessitating a change in procedure. To maintain the desired incident 

 wave conditions, only short bursts of waves (usually 10) could be generated 

 at a time, making the last two tests more time consuming and leading to a 

 shorter total duration of each wave condition. 



5. Surveys . 



Surveys were conducted from a movable platform, using a 5-inch-diameter 

 (12.7 centimeters) disc on the end of a 20-foot sounding rod. The elevation 

 of the structure and the sand near the toes was measured to the nearest 

 0.01 foot on a 2-foot (0.61 meter) grid along and across .the tank (Fig. 5). 

 The sand bed elevation was usually measured every 2 feet along the tank on 

 two ranges, 8 feet apart. 



In preparation for construction of structures II, III, and IV, the 

 graded sand bed was surveyed. The breakwaters were surveyed immediately 

 after completion, then after every 1 to 2 hours of wave action during each 

 wave condition. Seven profiles, one for each survey range shown in Figure 



5, were plotted from each survey. If comparison of profiles from consec- 

 utive surveys indicated continuing change, wave action was continued. If 

 the profile comparison indicated essentially no movement, the latest pro- 

 files were considered the stable profiles for their wave condition and 

 the initial profiles for the next wave condition. Visual observations of 

 structure movement during wave action were made for tests III and IV when 

 the breakwater crests were exposed. This aided in preliminary determination 

 of structure stability, but the final determination was based on the surveys. 

 A test was terminated when the structure reached stability under wave con- 

 dition d or, in the case of test IV, wave condition c. 



6. Test Descriptions . 



Each test description includes remarks on the breakwater construction, 

 wave conditions, differences in the test procedure, behavior of the bags, 

 and resulting changes in the breakwater configuration. The spacing of the 

 survey lines permitted the location of individual bags on the surface of 

 the breakwater and the determination of the processes which caused changes 

 in the structure configuration. Bag movements were observed by comparing 

 successive plots of the seven profiles derived from each survey, except for 

 visually observed motion at the top of structures III and IV. To illustrate 

 overall changes in configuration for each test, an average profile was 

 calculated and plotted from the survey at the beginning of the test and 

 the survey at the end of each wave condition. Changes in the structure 

 elevation, crest width, and face slopes are described from comparison of 

 the average profiles. 



Changes in bag arrangement were of three general types: settlement, 

 displacement, and slumping. Settlement or consolidation occurred when a 



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