at 0.25-ft increments, were measured. The 0.5 ft of structure next to each 

 wall was not considered because of the possibility of discontinuity effects 

 between armor units and the flume walls. Soundings were taken at the same 

 points once the armor was in place and again after the structure had been sub- 

 jected to wave attack. 



12. Sounding data from each stability test were reduced in the follow- 

 ing manner. The individual sounding points obtained on each parallel row were 

 averaged to yield an average elevation at the bottom of the armor layer before 

 the armor was placed and then at the top of the armor layer before and after 

 testing. From these values, the cross-sectional armor area before testing and 

 the area from which armor units were displaced (either downslope or off the 

 section) were calculated. Damage then was determined from the following 

 relation: 



^2 

 Percent damage = — (100) 



^1 



where 



2 

 A^ = area before testing, ft 



2 

 A„ = area from which armor units have been displaced, ft 



The percentage given by the WES sounding technique is, therefore, a measure- 

 ment of an end area which converts to an average volume of armor material that 

 has been moved from its original location (either downslope or off structure). 



Test Equipment 



13. All tests were conducted in a 5-ft-wide, 4-ft-deep, 119-ft-long 

 concrete wave flume with test sections installed about 90 ft from a vertical 

 displacement wave generator. A thin divider was installed in the center of 

 the test section area, thus yielding two 2.5-ft-wlde sections. The first 

 10-ft length of flume bottom, immediately seaward of the test sections, was 

 molded on a IV-on-lOH slope, while the remaining 80-ft length was flat. The 

 generator is capable of producing sinusodial waves of various periods and 

 heights. For all tests, waves of the required characteristics were generated 

 by varying the frequency and amplitude of the plunger motion. Changes in 

 water surface elevation as a function of time (wave heights) were measured by 



