ACE Basin Erosion
Edisto Beach is located in St. Helena Sound where the ACE Basin meets the Atlantic Ocean. The Ashepoo, Combahee and Edisto Basin (abbreviated as ACE Basin, spoken as ace basin) is one of the largest undeveloped estuaries along the Atlantic Coast of the United States. Located primarily in Colleton, Charleston, and Beaufort counties in South Carolina, the Ashepoo, Combahee and South Edisto rivers combine into the larger St. Helena Sound and drain a significant portion of the Lowcountry region.
Over the years the landscape of the ACE has eroded and taken on different shapes. This is no surprise due to coastlines being impermanent. Waters continue to rise causing flooding and transforming forests into wetlands. It is nature's job to reshape our coastlines and this one is no exception.
The ACE Basin’s rivers drain into Saint Helena Sound, delivering sediment that settles into the shoals and sandbars of an extensive delta, visible at low tide as seen in the picture above. The complex sediment patterns, known as bedforms, can change size and shape on a daily basis in response to currents, tides, and environmental conditions. The type of pattern shown above tends to form in shallow water moving at a high velocity.
What is a delta?
A delta is a low-lying, almost flat landform, composed of sediments deposited where a river flows into a lake or an ocean. Deltas form when the volume of sediment deposited at a river mouth is greater than what waves, currents, and tides can erode. Deltas extend the coastline outward, forming new land along the shore.
What is a groin (groyne)?
A groin, built perpendicular to the shore, is a rigid hydraulic structure built from an ocean shore or from a bank that interrupts water flow and limits the movement of sediment. This depletes the sand supply to the beach area immediately down-drift of the structure. Groins serve to prohibit erosion and stabilize a beach on the updrift side. It is usually made out of wood, concrete, or stone.
The negative impact of groins on downdrift shorelines is well understood. When a groin works as intended, sand moving along the beach in the so-called downdrift direction is trapped on the updrift side of the groin, causing a sand deficit and increasing erosion rates on the downdrift side.
QUESTIONS/TASKS:
1. What time and date did you visit? Using a little bit of research what was the tide level at the time of your visit?
2. What are the signs of erosion and coastline reshaping? What is contributing to the change in the coastline here? What if anything is in danger over time?
3. How many groins can you observe from this point? Why do you believe there are multiple groins in this stretch of beach?
4. To prove that you were here, please post a picture of yourself or your GPS with the sound in the background. Any other photos of the area are also greatly appreciated.