What makes Port Royal Sound different
from all other coastal areas?

1. No Real Rivers Are Present:
Unlike other coastal areas it does not receive freshwater from a river.  The named “rivers” are actually large salt water tidal waterways.  The Broad, Colleton and May Rivers are actually large salt water tidal waterways with flow from the ocean rather than from inland areas.  The only two freshwater inputs are the New and Coosawhatchie Rivers, but they drain relatively small areas of uplands and therefore contribute relatively small volumes of freshwater.  

2. Rising Sea Level Has Created a Flooded Landscape:
Rising sea level has slowly flooded the original coastal landscape transforming former valleys into deep tidal creeks and hilltops into islands surrounded by salt marsh.  Local tidal creeks and waterways are deep because there are no rivers emptying sediment into this system.  In contrast, coastal areas with rivers have remained shallow as sea level rose because of continued accumulation of sediment originating from these rivers.  As a result, 50% of Beaufort County is covered by marine waters.

3. Exceptionally High Tides Create Wide Expanses of Salt Marsh:
Port Royal Sound experiences the highest tides along the Atlantic coast south of Maine.  The tidal amplitude (difference between high and low tide) ranges from 6 feet during neap tides to over 10 feet during Spring tides.  These exceptionally high tides are created because of the concave curvature of the coastline between North Carolina and Florida.   Gravity from the moon pulls up a bulge of water on the ocean’s surface As the earth rotates eastward through this bulge, a large amount of water is pushed up against the continent, but the coastline’s curvature causes this water to be focused at the vertex of the curve, which happens to be the mouth of Port Royal Sound.

These exceptionally high tides are responsible for Beaufort County having at least 50% of South Carolina’s salt marsh.  Spartina alterniflora is the only species of plant that grows in salt water in temperate North America.  It thrives where it is submerged at least once a day by salt water, but its roots are also exposed to the air daily during low tides.  The lack of freshwater and the large areas of submerged coastal terrain in Beaufort County combine to create expansive marshes of Spartina alterniflora.