Table 2 



Baptiste Collette Bayou Jetties 



Mississippi River Outlets, Venice, Louisiana 



Date(s) Construction and Rehabilitation History 



1978- Two parallel jetties, spaced 520 ft apart, were constructed at the 

 1979 entrance to Baptiste Collette Bayou (Figure 5). With fairly imperm- 

 eable jetties in place, significant reductions in dredging would be 

 possible, thus reducing the overall cost of maintaining the Bayou 

 channel. These jetties are similar to those constructed at Tiger 

 Pass with the two waterways providing a shorter navigation route 

 between east and west gulf waters. The east jetty is 9,000 ft long 

 and extends 2,000 ft past the seaward end of the 7,000-ft-long west 

 jetty. A 20- by 250-ft channel is maintained between the jetties. 

 The east jetty (Figure 6a) was built in two geometric sections. The 

 lower section had a crown elevation of +3 ft mlg, a crown width of 

 26 ft, and 1V:3H side slopes. The upper section had a +6 ft mlg 

 crown elevation, a 4-ft crown width, and 1V:2H side slopes. The 

 lower section was composed of shell material for the core and bedding 

 layer (1-ft maximum thickness), followed by a 1.5-ft-thick layer of 

 graded stone (500-lb maximum) placed on the side slopes only, and 

 capped with a 2-ft-thick layer of graded stone (1,200-lb maximum) 

 placed on the side slopes and crown. Graded stone (5,000-lb maximum) 

 was placed in the upper section. The upper section was not 

 constructed on a portion (approximately 950 ft) of the jetty. The 

 west Jetty (Figure 6b) had a crown elevation of from +3 to +4 ft mlg, 

 a 26-ft crown width and 1V:3H side slopes. It was built up with a 

 bedding layer (1-ft maximum thickness) of shell and filled out with 

 graded (1,200-lb maximum) stone. Prior to construction, existing 

 ground elevations were from +3 to -6 ft mlg. Both jetties were built 

 on top of mostly soft clays and were expected to undergo large 

 settlements (up to 4 ft). Plastic filter fabrics of varying tensile 

 strengths were placed at four 500-ft-long test sections (2 sections 

 per jetty), prior or subsequent to placing shell material. Two 

 sections were at the seaward ends of the jetties and the remaining 

 two started 4,000 ft from the landward ends. Settlement plates were 

 placed at 80- to 90-ft intervals within test sections and at 500-ft 

 intervals elsewhere. These were placed to monitor settlement and the 

 effectiveness of the test sections. The total cost of construction 

 was about $2,192,000 using 17,400 sq yd of fabric, 41,000 cu yd of 

 shell, and 114,500 tons of graded stone. 



1984 Repairs were made on the seaward end of the west Jetty for a distance 

 of 4,550 ft, and the entire east Jetty was repaired (Figure 6c). 

 (These were called repairs even though the original design called for 

 two-phase construction.) Existing (1983 survey) center-line eleva- 

 tions on sections to be repaired were from +1 to +3 ft National 

 Geodetic Vertical Datum (NGVD) on the west jetty and from +2 to +5 ft 

 NGVD on the east jetty. (NGVD datum is about 0.5 ft above mlg 

 datum) . 



(Continued) 



15 



