6. The model was constructed at a nominal 1:16 (model :prototype) undis- 

 torted Froude scale. The influence of scale effects at this large a scale was 

 considered to be small. To further reduce the possibility of scale effects, 

 the stone used in the filter layer was double the size required for geometri- 

 cal similitude. Use of somewhat larger filter stones helps establish the 

 proper flow-regime in the model filter layer when the revetment is exposed to 

 wave action; see Broderick and Ahrens (1982). Large-sized filter stone and a 

 1:16 scale were used in both the NCE and the SAJ studies to minimize the in- 

 fluence of scale effects. 



7. Tests for this study and the SAJ study were conducted in a 61 -cm-wide 

 channel within the Coastal Engineering Research Center's (CERC's) 1.2- by 4.6- 

 by 42.7-m wave tank. Wave conditions were measured offshore by using three 

 parallel wire-resistance wave gages. Incident and reflected wave spectra were 

 resolved using the method of Goda and Suzuki (1976). Figure 2 shows a plan 

 view of the wave tank setup for this study. Details relating to spectral wave 

 generation and the analysis of wave conditions in this wave tank are given by 

 Seelig (1980). 



8. Maximum wave runup elevations were obtained by visual observations 

 made by an experienced observer, and quantified by using a point gage. The 

 observer stood immediately adjacent to the structure in a wave absorber chan- 

 nel as shown in Figure 2. The duration of the runup observation was 256 sec, 

 corresponding to the data acquisition system's sampling interval for the wave 

 gages to obtain the wave information. The observer tried to measure the ex- 

 treme excursion of "green" water near the middle of the structure. Observa- 

 tions were not intended to measure the upper limit of spray or splash. Prior 

 to using visual observations, some effort had been expended in trying to use 

 various types of continuous wave gages positioned just above the armor sur- 

 face, but runup elevations that were measured by the wave gages proved to be 

 unreliable. After some initial observations and discussion, two experienced 

 observers could obtain maximum runup elevations to within about a difference 

 of 3 percent or less of each other. Additional information about the NCE 

 study is given in Ahrens and Seelig (1980). 



9. The SAJ study was conducted to investigate the stability of and wave 

 runup on riprap to be used to protect Herbert Hoover Dike on Lake Okeechobee, 

 Florida. Two structural slopes were tested during this study, 1 on 4 and 1 on 

 3. Figure 3 shows a profile view of the 1-on-4 slope tested. Figure 4 shows 



