(prior to the 1960's) and large amounts of stone (during and after the 1960's) 

 have been required to keep these Jetties above mean high water (mhw) . The 

 only remaining Jetty with a concrete cap is the South Pass east Jetty. Land- 

 ward extensions have been made to at least one jetty at the following 

 projects: Bayou Fontanelle (part of the Empire to the Gulf of Mexico Waterway 

 Projects), Grand Isle, Bayou LaFourche, and Calcasieu Pass. Plastic filter 

 fabric has been tested on sections of the Jetties at Tiger Pass and Baptiste 

 Collette Bayou. 



5. The structures are fairly low crested, being built or maintained at 

 elevations from +3 to +6 ft mean low gulf (mlg). Typical design crown widths 

 are from 4 to 14 ft. Design side slopes were 1V:1.5H on most of the older 

 structures, while 1V:2H (or 1V:3H) usually has been used on the newer designs 

 and repairs. Cover stone sizes typically have been 1 to 6 tons with a maximum 

 of 10 tons used at the seaward ends of the South, Southwest, and Calcasieu 

 Passes Jetties. Several of the more recent repairs and designs have called 

 for graded stone, typically to 5,000 lb, placed by clamshell bucket. (The 

 most recent repairs to Southwest Pass used 2- to 4-ton stone.) Shell or 

 crushed bedding stone materials have been used as a core and bedding material, 

 acting as a filter layer for the larger stone. Advantages of shell are its 

 availability, lower cost than stone (per unit volume), and lower specific 

 gravity. 



6. Seven of the projects have had repairs since they were constructed 

 originally (chronologically, the oldest projects). Southwest Pass Jetties 

 have the most extensive repair history. South Pass jetties have not required 

 maintenance since 1970, and the channel has not been dredged since 1977. The 

 majority of repairs were needed due to overall subsidence of structures. 

 Steel sheet-pile Jetties were constructed originally at Bayou LaFourche but 

 were badly damaged within a year and had to be supplemented at the base with 

 rubble stone. The projects at Grand Isle, Bayou LaFourche, and Mermentau 

 River have had direct involvement by local or State interests in either their 

 original construction or subsequent repairs. 



7. General design of the structures has been concerned principally with 

 their settlement. The structures are not designed for hurricane conditions, 

 although they have been exposed to hurricane conditions in the Gulf of Mexico 

 since construction. None of the structures have been model tested for stone 

 slope stability. Hudson's equation and depth-limited wave heights are used 



