the data trends for F' less than 0.3 were not made and would probably not be 

 meaningful. 



23. Data analysis of the seawall/revetment configurations referred to 

 as the Cape Hatteras types is in a preliminary stage. This test series in- 

 cludes both vertical and recurved seawalls which have rather extensive revet- 

 ment toe protection (Figure 13). Overtopping data trend curves of the form of 

 Equation 2 are used in Figure 14 to compare the performance of the three Cape 

 Hatteras seawall/revetment configurations. The poor performance of the verti- 

 cal seawall compared to the walls with recurvature is clearly shown in Fig- 

 ure 14. Figures 15 and 16 show laboratory tests of the Cape Hatteras seawalls 

 with a typical curve and a vertical wall, respectively, that illustrate the 

 considerable difference in wave action that can occur at the wall for dif- 

 ferent structure geometries. It can be seen in Figure 14 that the wall with 

 severe recurvature is somewhat better than the wall with more moderate re- 

 curvature. In Figure 17, the overtopping trend curves for the Roughans Point 

 seawall profile shown in Figure 10 are compared to those for the vertical wall 

 Cape Hatteras profile shown in Figure 13. Figure 17 indicates that even a 

 rather small recurve can be effective since the Roughans Point overtopping 

 trend curve falls considerably below the corresponding curve for the vertical 

 Cape Hatteras seawall configuration. Figures 14 and 17 illustrate the value 

 of the overtopping model, defined by Equations 1 and 2, for evaluating the 

 performance of a single configuration and for making comparisons between and 

 among configurations. It should be noted that Equation 2 does not take into 

 account water blown over the wall by onshore winds which are usually present 

 during overtopping conditions. Therefore, a recurve which throws water sea- 

 ward and possibly even downward will control windblown overtopping better than 

 a vertical wall that throws the water straight upward. Figure 18 shows how 

 energetic wave action can send large quantities of spray to impressive heights 

 when waves encounter a steep barrier. Figure 18 was taken at Neach Bay, 

 Washington, with long-period waves propagating shoreward from the Strait of 

 Juan de Fuca and crashing against a riprap revetment with a slope of 1 on 2. 

 Fronting rubble and revetments 



24. A second method to reduce wave overtopping rates is to use rubble 

 in front of the wall. The purpose of the rubble might be toe protection, but 

 if enough rubble is used, the dissipation of wave energy will be sufficient to 

 reduce wave overtopping. The extensive toe protection used for the 



22 



