Charleston Harbor Jetties

 

Charleston, South Carolina, SAC

 

Date(s)            Construction and Rehabilitation History

 

1878-1886       Rubble-mound jetties with a shoreward submerged weir section and seaward raised section were constructed at Charleston Harbor to provide (in conjunction with dredging) for a navigation channel 21 ft mlw deep. The total lengths of the north and south jetties were 15,400 ft and 19,100 ft, respectively. The distance between the parallel seaward sections of the jetties was 2,900 ft.  Shoreward portions of both jetties, each approximately 6,000 ft long, were built up to typical depths of -4 to -12 ft mlw (rising only a few feet above the bottom, with low sections as deep as 15 ft and 28 ft on the north and south jetties, respectively). The outer 7,200 ft of the north jetty was raised to an average of +7 to +8 ft mlw, the outer 9,200 ft of the south jetty was raised to an average of +10 ft mlw, and shoreward of this section an additional 2,400 ft was raised to +8 ft mlw. A typical section of the raised jetties consisted of a log and brush mattress foundation loaded with 30 to 60 tons of small stone weighing 10 to 250 lb. An additional narrow course of small stone was placed, and 1- to 7-ton granite blocks were placed as cover stone. Typical crest widths were 12 to 15 ft.

 

1935                Only minor dredging between the jetties has been required since the project depth was increased in 1917 to -30 ft mlw. Field survey showed very little deterioration to the submerged or raised portion of the jetties.

 

1966                Present channel depth of -35 ft mlw has been maintained since 1961.  An inspection survey in August 1966 indicated a general subsidence of 1.5 to 3.5 ft along the raised portion of the jetties, with maximums of 5 and 6 ft over short sections of the north and south jetties, respectively.

 

1985                Present channel depth (-35 it mlw) extends approximately 13,000 ft beyond the end of the jetties. There has been no history of maintenance or repair to the jetties since their completion.