ROCK OVERLAY 



Overloy Rock 

 Filter 

 SECTION 







., Jsr"^ S 



Rock overlay in large wave tank at the 

 Coastal Engineering Research Center (CERC) . 



Prototype Installation : 

 Lake Oahe, South Dakota. 



Railroad embankment in Lake Oahe near Mobridge. 

 Existing riprap bank damaged by 5-foot-high waves. 



Rock overlay- (all rocks touching) was used to upgrade the slope 



stability. 



Overlay design wave H = 5 feet. 



Overlay stable after 3 years (McCartney and Ahrens , in preparation t 1976) 



Wave Tank Tests : 



Overlay tested in both large and small wave tanks (McCartney and 



Ahrens, in preparation, 1976). 



Tests only for 1 on 3 slope and 3.67-period waves. 



Overlay has stability equal to two layers of riprap for zero damage; 



however, overlay had only one-half the reserve stability as two 



layers of riprap. 



Design Factors : 



Zero- damage wave height: Depends on rock size. 



Wave runup: 0.5 compared to smooth slope. 



Wave reflection: Low. 



Remarks : 



Overlay could be used to upgrade a damaged riprap slope or as 

 original construction. 



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