(5) Problems . Fire Island Inlet is located on the south shore 

 of Long Island, and is the primary waterway for boat traffic between the 

 Atlantic Ocean and Great South Bay (Fig. 7-11). The inlet is about 3,500 

 feet wide with depths to about 25 feet MLW. The western end of Fire 

 Island migrated westerly a distance of over 4 miles between 1825 and 1940, 

 when this migration was arrested by the construction of the 5, 000- foot 

 Federal jetty which extends generally southwest toward the ocean. The 

 jetty trapped the littoral drift for about 10 years, then sand began by- 

 passing the structure and filling the navigation channel. Corrective 

 measures designed to alleviate channel deposition problems and supply 

 sand for down-beach nourishment (completed in December 1959) consisted 



of (a) dredging an extensive area to -18.0 feet through the mouth of the 

 inlet, (b) using a part of the material to construct a sand dike across 

 the deep channel adjacent to Oak Beach, and (c) depositing an ample sup- 

 ply for down-beach nourishment in a feeder beach area. The sand dike 

 was effective in diverting maximum currents from Oak Beach toward the 

 center of the inlet; however, the entrance channel was not stabilized 

 and continued to migrate as a result of accretion west of the Federal 

 jetty. 



(6) Purpose of Model Study . The Fire Island Inlet model study 

 was conducted to: 



(a) Investigate the proposed design of a combination 

 sand bypassing and channel maintenance procedure, consisting 

 of a littoral trap, a rehandling basin, an entrance channel 

 connecting the two, and a training dike, as recommended by the 

 U.S. Army Engineer District, New York, for Fire Island Inlet; 



(b) investigate effects of changes in the dimensions 

 and depths of the channel, trap, basin, and dikes through the 

 physical model; 



(c) determine the need for extending the Federal jetty 

 (estimated cost about $2,650,000 for 1,000 feet in 1963); 



(d) determine the need for additional dikes; and 



(e) establish locations and dimensions of any addi- 

 tional improvements needed to increase the effectiveness of 

 the plan and maintain a stable channel through the inlet. 



Many alternatives and modifications of the original plan were tested 

 during the study to ensure that all possibilities had been investigated 

 for the best overall solution to the problems. 



(7) The Model . The model reproduced a 60-square mile area that 

 included all of Fire Island Inlet and the ocean beaches from Fire Island 

 light on the east to beyond Gilgo on the west, along with a part of the 

 Atlantic Ocean (Fig. 7-11). The Atlantic Ocean part of the model ex- 

 tended 5 miles to the east of and 7.5 miles to the west of the Federal 



497 



