FIGURE 2-2 



COASTAL WETLAND HABITATS 



Highland 47% 



z 

 g 



< 



> 



HO 

 .8 



46 



♦ 4 

 ♦2 

 



-2- 

 -4 

 -6 

 -8 



Tidal Flal 6°/ 



Waler 27% 



- 10- YR STORM 



-PEAK YEARLY TIDE 



- SPRING HIGH WATER 



- MEAN HIGH WATER 

 -NEAP HIGH WATER 



-MEAN SEA LEVEL 



- MEAN LOW WATER 



■ SPRING LOW WATER 



♦ 10 



♦ 8 



♦ 6 



♦ 4 



♦ 2 

 ■ 



2 

 1--4 



-6 

 -8 



1000 



2000 3000 



TYPICAL DISTANCE (FT ) 



4000 



5000 



The Charleston area has a complex morphology. Besides the three tidal rivers that converge 

 in the area, numerous channels dissect it, exhibiting dendritic drainage patterns typical of 

 drowned coastal plain shorelines. 



A back-barrier, tidal creek/marsh/mud-flat system near Kiawah Island, approximately 20 km 

 south of Charleston, has a typical drainage pattern. Throughout the area, highlands are typically 

 less than 5 m (16 ft) above mean sea level. With a mean tidal range of 1.6 m (5.2 ft), a broad area 

 along the coastal edge is flooded twice each day. The natural portions of Charleston Harbor are 

 dominated by fringing salt marshes from several meters to over one kilometer wide. 



The upper limit of the marsh can usually be distinguished by an abrupt transition from 

 upland vegetation to marsh species tolerant of occasional salt-water flooding. Topographic maps 

 of Charleston generally show this break to have an elevation of about 1.5 m (+5 ft). Along the 

 back side of Kiawah Island, just south of the case study area, one can observe such an abrupt 

 transition between highland terrestrial vegetation and the marsh area. Where the waterfront is 

 developed, the transition from marsh or tidal creeks to highland can be very distinct because of 

 the presence of shore-protection structures, such as vertical bulkheads and riprap. Another 

 marsh/tidal-flat system located behind Isle of Palms and Dewees Island, just outside of the 

 Charleston study area, contains a mud flat and circular oyster mounds near the marsh and tidal 

 channels. Oyster mounds were found at a wide range of elevations along tidal creek banks, but 

 over tidal flats most were common at elevations of 3046 cm (1.0-1.5 ft). 



Large portions of the back-barrier environments of Charleston consist of tidal flats at lower 

 elevations than the surrounding marsh. The most extensive intertidal mud flats around 

 Charleston generally occur in the sheltered zone directly behind the barrier islands. They are 

 thought to represent areas with lower sedimentation rates (Hayes and Kana 1976) away from 

 major tidal channels or sediment sources. 



Much of the Charleston shoreline has accreted (advanced seaward and upward) during the 

 past 40 years (Kana et al. 1984). Marshes accrete through the settling of fine-grained sediment on 

 the marsh surface, as cordgrass (Spartina altemiflora) and other species baffle the flow adjacent 

 to tidal creeks. Marsh sedimentation has generally been able to keep up with or exceed recent 

 sea level rises along this area of the eastern U.S. shoreline (Ward and Domeracki 1978). Much of 

 the sediment into the Charleston area derives from suspended sediment originating primarily 

 from the Cooper River, which carries the diverted flow of the Santee River (until planned 

 rediversion in 1986; U.S. Army Corps of Engineers, unpublished general design memorandum). 



41 



