Let’s first define a sound and describe some of the geological features that make up the Port Royal Sound Area. A sound is an ocean channel between two bodies of land, yet still accessible by ocean-going vessels. This means that the channels, which are relatively shallow and narrow bodies of water, are deep enough to allow deep-hulled ships to pass through unscathed.
The Port Royal Sound Area also is sometimes referred to as an embayment of the Atlantic Ocean. A bay is a body of water connected to the ocean and formed by the indentation of the shoreline. In our case, the embayment would include all the rivers, marshes and islands that we are familiar with here in Beaufort County.
The characteristics that best describe a sound:
- Ocean influenced.
- Encompassed by land.
- Either of significant depth or significant size.
Almost all of the rivers and creeks in Beaufort County and the Port Royal Sound watershed are not what we traditionally think of as rivers. Port Royal Sound rivers don’t have a headwater originating inland, either in the mountains (brown-water rivers) or in the coastal plain (black-water rivers), with fresh water flowing toward the ocean. Instead, ocean tides drive water flow in the Port Royal Sound Area rivers. The area has exceptionally high tides (eight-plus feet) because of its geographic location. These high tides drive ocean water through a network of tidal rivers and creeks that extend 20 miles inland. Tidal creeks are easily recognized at a distance because they are bordered by grasses and rushes that can tolerate regular salt-water flooding. Low tide reveals muddy banks pockmarked with thousands of holes made by fiddler crabs and bordered by intermittent oyster beds.
Encompassed by Land
The salt marsh is a coastal wetland flooded and drained by water brought in and out by the ocean’s tides. The low marsh, which is flooded daily by high tides, is made up of a monoculture of Spartina alterniflora. Spartina alterniflora is the only plant that can tolerate daily inundation by salt water. The high marsh is the area only flooded during exceptionally high tide events. It is characterized by two species of plants – black needle rush and glasswort. The upper boundary separating a salt marsh from the adjacent upland is characterized by plant species that can tolerate infrequent flooding by salt water. These include Spartina patens and and ox-eye daisy.
A hummock is a small island surrounded by salt marsh and typically vegetated with evergreen trees and shrubs that can tolerate salt spray. Some local hummocks consist almost exclusively of oyster shell discarded by hundreds of generations of pre-Columbian Indians. These hummocks also are called “shell middens.” Typically, hummocks are high enough in elevation that they are able to sustain a small forest ecosystem, but are not large enough to support large animal populations. They do support populations of smaller animals, such as lizards, birds and insects, and they provide resting places for larger mammals and birds. Hummocks rich in oyster shell may support plant species not found elsewhere.
The uplands comprise islands and mainland that are high enough in elevation that they only flood during severe storms, such as hurricanes. Although above the high tide line, uplands still are connected to the salt marshes and tidal creeks because groundwater carrying nutrients, and in some cases pollutants, seeps from the uplands into the adjacent marshes.
Significant depth or size
There are three sounds in our area:
- Port Royal Sound. A body of water between northern Hilton Head Island and southeastern Saint Helena and Parris islands.
- Calibogue Sound. A body of water between southern Hilton Head and Daufuskie islands.
- Saint Helena Sound. A body of water between northwestern Saint Helena and Edisto islands.
The Port Royal Sound Area includes Port Royal Sound and Calibogue Sound. These two sounds are interconnected and have very similar ecological traits, so are usually viewed as one system. The Saint Helena Sound system is much different from the Port Royal Sound system due to the large inflow of fresh water from the ACE Basin. As a result, the species composition is much different.
The Port Royal Sound Area encompasses all the areas directly affected by the water flowing into Port Royal or Calibouge sounds. This includes such rivers as the Beaufort, Broad and May, as well as all their tributaries. The Port Royal Sound Area is much larger than many people realize. It extends almost all the way to Interstate 95 and covers most of Beaufort County, as well as portions of Jasper and Hampton counties. All told, the Port Royal Sound Area comprises nearly 1,600 square miles of land, marsh and river.
For more on information, check out the Port Royal Sound episode of “Coastal Kingdom.”