PART IV: WAVE RUNUP AND OVERTOPPING OF REVETMENTS 



30. In some instances wave overtopping of a revetment occurs because 

 the extent of wave runup is underestimated. Figure 23 shows a riprap revet- 

 ment in New Haven, Connecticut, which was overtopped by wave action caused by 

 Hurricane Gloria in 1985. Grouting of this riprap might have made the wave 

 runup problem worse by making the revetment effectively smoother and thereby 

 increasing the amount of overtopping. Ponding due to overtopping creates a 

 hydraulic head which will cause fine particles to migrate out through the re- 

 vetment if filter layers are not properly constructed. Loss of fine material 

 from behind the revetment will eventually cause a collapse of the structure. 



A similar problem is shown in Figure 24 where storm waves from Hurricane Hilda 

 (1964) overtopped the west jetty at Panama City, Florida. Ponding behind the 

 jetty caused sand to migrate through the structure creating "sink" holes. 

 Generally, small amounts of sand loss are not a problem since a jetty is free 

 standing, but deep sink holes could undermine the heel of the jetty and cause 

 the structure to slump. 



31. Methods to alleviate wave overtopping of revetments obviously in- 

 clude increasing the thickness of the armor layer, using a quarry stone over- 

 lay (McCartney and Ahrens 1976) , or possibly building a berm on the riprap 

 revetments. The value of a berm was discussed under the topic of reducing 

 wave overtopping of seawalls. A parapet could be used on a riprap revetment 

 or a block revetment to reduce overtopping. An extension of the berm concept 

 is to use an offshore breakwater in front of the revetment to reduce the 

 severity of wave action on the revetment (Markle 1981; Powell and Allsop 

 1985) . A modification of the offshore breakwater concept is to incorporate an 

 underwater sill into the toe of the revetment to introduce premature wave 

 breaking. Offshore breakwaters, sills, and berms provide a progression of 

 possible solutions which seem promising for some situations, such as protec- 

 tion of El Morrow Castle, in San Juan, Puerto Rico (Markle 1982), but these 

 solutions generally are expensive compared to the use of a parapet. The value 

 of a parapet is probably similar to the value of a cap in increasing the 

 height of a seawall, as shown in Figure 22. 



32. In low-lying locations it is often impractical to build a revetment 

 high enough not to be overtopped. However, even for these situations adoption 

 of effective strategies for reducing wave runup and overtopping will improve 



34 



