Chapter 2 



CHARLESTON CASE STUDY 



by 



Timothy W. Kana, Bart J. Baca, and Mark L. Williams 



Coastal Science & Engineering, Inc. 



P.O. Box 8056 



Columbia, South Carolina 29202 



INTRODUCTION 



This chapter examines the potential impact of future sea level rise on coastal wetlands in the 

 area of Charleston, South Carolina, for the year 2075. We investigate the hypothesis from 

 Chapter 1 that a generally concave marsh profile implies that a rise in sea level would cause a net 

 loss of wetlands. The chapter builds upon previous EPA studies that had assessed the potential 

 physical and economic impacts of sea level rise on the Charleston area. 



We surveyed twelve wedand transects to determine elevations of particular parts of the 

 marsh, frequency of flooding, and vegetation at various elevations. From these transects, we 

 developed a composite transect representing an average profile of the area. Using this informa- 

 tion and estimates of the sediment provided by nearby rivers, we then estimated the shifts in 

 wetland communities and net loss of marsh acreage associated with three possible scenarios of 

 sea level rise for the year 2075: (1) the current trend, which implies a rise of 24 cm (0.8 ft), 

 relative to the subsiding coast of Charleston; (2) a low scenario of 87 cm (3.0 ft); and (3) a high 

 scenario of a 159-cm rise (5.2 ft). 1 



We examine background information concerning global warming and future sea level rise, 

 the ecological balance of coastal wetlands, and the potential transformation of these ecosystems 

 as sea level rises. Next, we examine the wetlands in the Charleston study area and describe a field 

 study in which we developed wetland transects. Finally, we discuss the potential impact of future 

 sea level rise on Charleston's wedands, and suggest ways to improve our ability to predict the 

 impact of sea level rise on other coastal wedands. 



Ecological Balance of Wetlands 



Recent attention concerning rising sea level has been focused on the fate of economic 

 development in coastal areas. However, the area facing the most immediate consequences would 

 be intertidal wetlands. Lying between the sea and the land, this zone will experience the direct 

 effects of changing sea levels, tidal inundation, and storm surges. 



The intertidal wetlands contain productive habitats, including marshes, tidal flats, and 

 beaches, which are essential to estuarine food webs. The distribution of the wetlands is sensitively 

 balanced for existing tidal conditions, wave energy, daily flooding duration, sedimentation rates 

 (and types), and climate. Their elevation in relation to mean sea level is critical to determining 

 the boundaries of a habitat and the plants within it, because elevation affects the frequency, 

 depth, and duration of flooding and soil salinity. For example, some marsh plants require 

 frequent (daily) flooding, while others adapt to irregular or infrequent flooding (Teal 1958). Along 

 the U.S. East Coast, the terms "low marsh" and "high marsh" are often used to distinguish 

 between zones (Teal 1958; Odum and Fanning 1973) that are flooded at least daily and zones 

 flooded less than daily but at least every 15 days. Areas flooded monthly or less are known as 

 transition wedands. 



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