Table 4 



Southwest Pass Jetties 



Southwest Pass, Louisiana 



Date Construction and Rehabilitation History 



1898- In 1898 a board appointed to report on Improvement of Southwest Pass 

 1908 recommended construction of two jetties. As a result of successful 

 Improvement of South Pass, commerce of the Port of New Orleans 

 rapidly increased and a deeper channel was desired to meet growing 

 demands of navigation. The act of 13 June 1902 approved construction 

 of the Southwest Pass Jetties. Jetty construction was started in 

 1904 and completed in 1908. The Jetties were built up using tiers of 

 fascine mattresses, each tier ballasted with stone and sunk. 

 Mattress widths varied from 35 to 150 ft. The wider mats were placed 

 on the bottom, and the number of tiers depended on the water depth. 

 The top tier was placed at about mlw, a 1- to 3-ft- thick layer of 

 riprap stone was placed to mhw, and a 12-ft-wide concrete cap was 

 cast in place to a finished grade of +4.5 mhw. The east and west 

 Jetties were 21,000 and 15,000 ft long, respectively, and converged 

 from a distance of 6,000 ft apart to a distance of 3,600 ft (Fig- 

 ure 12, existing layout). The authorized channel was to have a depth 

 of 35 ft and a width of 1,000 ft. The total cost of construction was 

 $2,630,000 using 1,086,000 sq yd of mattress, 328,300 tons of stone, 

 and 44,500 cu yd of concrete. 



I9IO- The jetties were extended seaward — the east jetty 2,900 ft and the 

 1912 west jetty 3,400 ft. The seaward ends were approximately 3,200 ft 



apart. Spur dikes were constructed in the lower 7 miles of the pass, 

 including the Jettied section, contracting the channel width to about 

 3,000 ft. Materials used in the jetty extensions were 286,000 sq ft 

 of mattress and 121,000 tons of stone. An additional 9,800 tons of 

 stone was used at the inner ends of the jetties. Total cost of the 

 extensions and repairs was $903,000. 



1914_ The Jetties and extensions as originally built had settled to the 

 1918 point that considerable amounts of water overflowed the concrete and 

 stone capping during high tide. To prevent this overflow, additional 

 stone was placed on the outer sections, and concrete capping was 

 placed along inner sections of the Jetties. The outer 8,000- and 

 11,000-ft sections of the east and west Jetties, respectively, had 

 75- to 2,000-lb marble stone (170 lb/ft-') placed on the seaside of 

 the existing concrete cap. The stone was placed from +1 to +2 ft mhw 

 with 4- to 10-ft crown widths and natural side slopes. A total of 

 121,700 tons of stone was placed at a cost of $567,900. In I916, 

 approximately 9,180- and 6, 150-ft-long sections of the east and west 

 Jetties, respectively, were capped with concrete. Except for 66O ft 

 of the east Jetty, the new cap sections were placed landward of 

 ongoing stone repairs. The 3-ft-wide cap was placed on the existing 

 cap to an elevation of +3 ft mhw. A total of 5,396 cu yd of concrete 

 was used at a total cost of $55,600. 



(Continued) 



25 



