chart paper by an electrically operated oscillograph. The electrical output 

 of the wave gages was directly proportional to their submergence depth. 



Selection of Test Conditions 



14. Breaking wave tests were conducted using both tribar and dolos 

 armor overlays. A review of past site-specific stability projects and hydro- 

 graphic data showed that typical prototype sea-bottom slopes could range from 

 almost flat to as steep as IV on lOH. Severity of breaking action increases 

 as bottom slope increases and since time restraints would allow testing of 

 only one foreslope, it was decided to use a IV-on-lOH slope, thus ensuring 

 severe depth-limited breaking wave action (plunging breakers) . When breaking 

 directly on the structure, this type of wave normally causes the most damage 

 to rubble-mound structures. 



15. By nondimensionalizing design conditions from site-specific proj- 

 ects, it was found that a relative depth (d/L) range of 0.04 to 0.14 should 

 include most prototype conditions encountered in breaking-wave stability 

 designs. A review of capabilities of the available flume and wave generator 

 showed that this range of d/L values could be achieved for a reasonable 

 range of testing depths. 



16. The wave flume was calibrated for depths from 0.40 to 0.95 ft in 

 0.05-ft increments at d/L values of 0.04, 0.06, 0.08, 0.10, 0.12, and 0.14. 

 This range of depths, and consequently breaking wave heights, proved to be 

 compatible with the selected armor weights and sea-side breakwater slopes. 



17. All stability tests were conducted on sections of the type shown in 

 Figure 1 and Photos 1-3. Sea-side slopes of IV on 1.5H and IV on 2H were in- 

 vestigated while the beach-side slope was held constant at IV on 1.5H. 

 Heights of the simulated existing structures (prior to placement of the dolos 

 or tribar overlays) varied from 1.0 to 1.4 ft. The height necessary to pre- 

 vent wave overtopping of the existing structure was determined from slopes and 

 estimated water depths and wave heights to be investigated in determining 

 stability coefficients (K's) for the dissimilar armor overlays. 



18. It was assumed that the existing armor stone was only marginally 

 stable and the dolos and tribar overlays would have K equal to those 

 obtained in new construction. Based on these assumptions, the stable tribar 

 weights would be approximately equal to the weight of the existing armor stone 



10 



