After the Civil War things changed along the shoreline once again in 1878 when construction was begun on the Charleston harbor entrance. The north and south jetties which are two parallel rock walls were built creating a 3-mile long offshore canal starting from Morris Island (south jetty) and Sullivan’s Island (north jetty). Work began on the north jetty from Sullivans Island, starting 1800 feet east of the Bowman Jetty, in December 1878. The construction of the south jetty started on Cummings Point. The walls move toward each other and narrow as the canal extends into the Atlantic Ocean. The walls are as wide as 208 feet at their base. The jetties took 17 years to complete and required 1.1 million tons of stone. The channel at the start was 9 feet deep but over the years has been deepened to 52 feet. The jetties can be seen as a fine line in the water on satellite images below.
In the following two pictures taken from the shore of Fort Moultrie you can see the south jetty on Morris Island as it enters the ocean. The Morris Island Lighthouse is in the background on the other side of the jetty.
This project was followed by the erosion of a large portion of Morris Island, and Folly Island lost several streets while Sullivan’s Island slowly accreted. In February of 2020 repairs to the south jetty were completed by the U.S. Army Corps of Engineers. Recent hurricanes caused further shoreline erosion on Morris Island, at the point where the south jetty tied into land, causing the rocks on the island to degrade. Without repair, increased erosion would give water a new path behind the jetty, lessening its effectiveness. The picture below shows the changes that have occurred in the shoreline over time. Folly Island has not undergone as much erosion as Morris Island because fresh loads of sand have been added on Folly Beach five times in the last three decades, another edition is planned for 2024.
Captain Abbot who supervised the last 10 years of construction on the north jetty and south jetties would carry out additional work on Sullivan’s Island. Before he began construction on Battery Jasper in 1897 he constructed an additional 440 feet of eight-foot above-grade timber sea walls. He protected this barricade from damage by an eight-foot wide large irregular shaped stone boulder riprap wall between the seawall and ocean. An additional 3000 feet of this type of wall was created in the first decade of the 20th century to extend it to Station 18 Street. Seawall was also added on the west side of Fort Moultrie as well. See maps below.
This map shows the timber and riprap seawall that Captain Abbot created and how much accretion of soil has occurred beyond the wall toward the ocean.
In the the image below, to the left on the west side of the island, you can see additional the zigzag riprap seawall.
Additional jetties were created over time such as the station 12 jetty.
A maritime forest began to appear along the shoreline near Fort Moultrie over time as shown below.
When jetties are placed in the path of the natural north south flow of silt along the Atlantic Coast they result in silt accretion north of the jetty but loss of sand and soil south of the jetty from natural processes unless something else is done. Interventions to block erosion could include a seawall (Sullivan’s Island) or adding back the lost sand (Folly Island). The immediate area south of the jetty will now erode which is what happened in the case of Morris Island. This is illustrated as shown in a previous figure by the case of the current Morris Island lighthouse. It was originally constructed over 1/2 mile from the ocean’s edge atop 264 timber piles in the 1870s. By 1938 the lighthouse which was originally 2,700 feet from the shore was now at the water’s edge. Today it is now 2000 feet off-shore showing how much of the island has been lost to erosion over time.
Learn more about efforts to preserve and save the Morris Island Lighthouse at these links- Save the Light, and Morris Island Lighthouse Friends.
Sources
Rock Solid: How the jetties and the grillage changed Charleston Harbor. Suzannah Smith Miles Special to the Moultrie News, Oct 12, 2020. Link
Remembering the Legacy of Coastal Defense: How an Understanding of the Development of Fort Moultrie Military Reservation, Sullivan’s Island, South Carolina, Can Facilitate its Future Preservation by Karl Philip Sondermann Clemson University Tiger Prints Link
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