as well as stabilize them to the existing armor stone structure. This design 

 proved to be unsuccessful. Scour initiated at the toes of the mats and, as 

 the mats subsided into the scour holes, they pulled the mats and armor stone 

 off the upper slope which resulted in general deterioration of the jetties. 

 Subsequent repairs were carried out by placing a toe berm of 100- to 200-lb 

 stone and, where needed, overlaying the old structure with additional armor 

 stone. 



21. Toe scour also has been noted as a problem with the jetties at East 

 Pass Channel and St. George Island, Florida, and Perdido Pass Channel, 

 Alabama (Figures 23-25, respectively). Scour on the channel side of the east 

 jetty at East Pass is so severe that it is thought that portions of the jetty 

 may slide into the channel at any time. In the past, this type of slippage 

 failure has caused severe damage to the west jetty at Panama City. 



22. Jetties at St. George Island have suffered cover stone loss result- 

 ing from the undermining action of toe scour. The west jetty at Perdido Pass 

 presently has significant amounts of toe scour on the channel side, and Hurri- 

 cane Frederick produced significant amounts of toe scour on the east jetty. 

 The overall condition of the Perdido Pass jetties was said to be good; there- 

 fore, it is assumed that the toe scour has not caused any obvious damage above 

 the waterline. 



Wilmington District 



23. The 3,650-ft-long rubble-mound north jetty located at Masonboro In- 

 let, North Carolina (Figure 26), was constructed between August 1965 and June 

 1966. The north jetty required extensive repair on the channel-side toe of 

 the outer rubble-mound structure in 1969 and to the channel-side toe of the 

 inner weir section in 1973. This was prior to construction of the south 

 jetty (14- to 22-ton armor stone) in 1980. It was thought that ebb and flood 

 flows had caused the channel to move adjacent to the north jetty, creating the 

 scour problem. In both repairs, a 2- to 3-layer protection of bedding mate- 

 rial and riprap (25 to 2,000 lb) was used. This toe protection butted against 

 the existing armor stone toe or sheet-pile weir. The berm width varied from 

 30 to 50 ft. It is thought that this work had limited success because the 

 jetty has not totally deteriorated, but it is presently in need of repair work 

 in several areas. Presently it is unknown whether the deteriorated appearance 

 of the north jetty results from a toe scour problem or from the possibility 



35 



