3.2.2 Stone count method 



Hedar (1960), Owen and Allsop (1983), Hughes (1993), and Davies et al. 

 (1994) describe measurement of damage through stone counts. Besides visual counting 

 during the test, photo overiays and digital image processing software can be used to 

 determine damage by stone counts; but these methods are relatively complex and time 

 consuming. Stone count methods are useful for determining very low damage values 

 but become inaccurate if more than a few stones begin to move or if movement is due to 

 sliding rather than dislodgement of individual stones. Stone count suffers from the 

 same weaknesses as the eroded volume method, namely that the spatial concentration of 

 damage is generally not specified and the maximum depth of erosion is not computed. 

 Stone count is also somewhat subjective. 



3.2.3 Recent damage measurement methods 



Davies et al. (1994) provided a review of laboratory techniques for 

 measuring breakwater profiles and methods for characterizing damage. They described 

 the WES damage D% (SPM 1984) as a visual displaced stone count and made no 

 reference to the WES eroded volume method. They introduced a technique to compare 

 the stone count method of damage measurement with the damage index method of 

 Broderick and Ahrens (1982). For damage measurement, they used a semiautomated 

 profiler that measured profiles with a small spatial sampling interval by dragging a 

 wheel over the structure face. During an experiment measuring damage on a riprap 

 armor layer, they computed the damage index, apparently using an average profile, and 



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