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Folly Island, 20km south of Charleston, South Carolina, is a barrier island. It has marketed itself and its beach as the “Edge of America,” and attracts thousands of tourists each year. Folly Beach is Folly Island’s most valuable resource. Folly Beach acts as a barrier against storm damage, an economic source, a recreational area for thousands of people per year, and a habitat for a variety of wildlife. In 1896, the US Army Corps of Engineers completed the construction of two jetties in Charleston Harbor. According to Folly Beach Renourishment, the purpose of these three-mile-long jetties extending from Sullivan’s Island to Morris Island was to help the arrival of container ships to the port by preventing sediment from accumulating on the Harbor and therefore making ship movement easier and as expected, the port industry grew-- but not without having negative impacts on the geological processes in the area. Sediment flow was disrupted, keeping Folly Beach from receiving the sand needed to protect itself from erosion. This has been even more aggravated by occasional hurricanes, most notably Hurricane Hugo in 1989. Since 1854, as recorded by the City of Folly Beach, the beach has retreated over 1,000 ft. landward, creating concern and sparking action in the form of beach renourishment funded by the US Army Corps and the local Government. In this paper, I will focus on the causes of erosion in Folly Beach, the measures taken to stabilize the beach, and what the results tell us about beach restoration in this area
Located 20km south of Charleston, South Carolina, Folly Beach extends for approximately 10km (6.2 miles) (Appendix 1 Map) on Folly Island, a barrier island pertaining to the Sea Islands of the Atlantic Ocean. The formation of this island started approximately 5,000 years ago with the decline of sea-level rise caused by the melting of the Pleistocene glaciers (Hippensteel, 2008). This gave way to the formation of beach ridges, one of which eventually became Folly Island. In its original state, this island would have been inhabited by pine forest and backed by marginal-marine marshes or possibly a lagoon, and although pine forest predominated in the island during the Civil War, less than 20% of the island is wooded as of now. During the past 200 years, around the 1860s, Folly Island was breached by inlets and therefore subdivided into Little Folly and Big Folly Island. Little Folly is the smaller northern part, and Big Folly is the larger southern part of the island. Come the 1930s, this inlet was crossable during low tide, by the 1940s, it was not crossable only during the highest tide. A road was built over the inlet in the 1950s, merging both subdivisions to form what we call today Folly Island (Levine et al, 2009).
“Folly Island is a mixed-energy, mastoidal island that is approximately 8 km long and ranges in width from approximately 80 m to more than 800 m” (Hippensteel, 2008). The island is divided from southern Kiawah Island by Stono Inlet and from northern Morris Island by Lighthouse Inlet (Levine et al, 2009). Furthermore, a single road passage connects Folly Island to the mainland, crossing the marshland and four sets of what used to be fellow barrier islands.
Wind, waves, and sediment supply determine the beach’s shape and stability, but storm-created changes are clearly seen and easily acknowledged, while the less apparent long-term sediment transport patterns are mostly left unnoticed even though these are constantly reshaping the coast (Levine et al, 2009). Waves come primarily from the northeast and crash against the slight slope of the beach, producing a longshore water current that proceeds to flow towards the southwest. Moreover, Folly Beach has a mean tidal range of 1.6 m, and an average wave height of 0.6 m (the lowest being 0.2 and the highest 2.5 m). These processes are the ones in charge of shaping and reshaping the coast naturally.
Erosion is a natural process. Most of the barrier islands in the United States that protect our East Coast have retreated landwards over time as a natural response to sea level rise, storms, etc. (W.C. Schwab et al. 2009) But most of the problem in Folly Island originates from Charleston Harbor’s jetties (Figure 1). With waves that come from the northeast, the jetties sequester the sand brought by the longshore current flowing south-southwest and prevent it from accumulating on Folly Beach’s shore (Levine et al. 2009). The jetties also destroyed Charleston’s tidal delta, according to FBR, which once reduced the impact of waves and was a natural sand source. The rates of change in this part of South Carolina’s coast vary from 8.0 m yr -1 erosion to 0.35 m yr -1 accretion (W.C. Schwab et al. 2009). This modified flow of water and sediment caused Folly Beach to retreat, showing its first signs in 1930. In a report done by Restore Folly Beach and commissioned by the Charleston County Committee associated all of the erosion to the jetties. It is also reported that Folly Beach’s shoreline is now over 800 feet landward compared to where its placement would be if the jetties had never been built (Platt et al. 1991). An example of this is The Morris Island Light. This lighthouse once sat on land more than 1,000 from the shoreline, but it now stands on a tiny constructed island between the shores of Morris Island and Folly Beach, hundreds of yards out to sea and surrounded by water on all sides. The lighthouse has been decommissioned for years (Rackley, 2018) and now only serves as a photo prop for tourists and a stark marker of severe beach erosion plaguing South Carolina’s coast.
In addition to ongoing erosion, South Carolina’s coast has suffered the effects of numerous storms. Located on the East Coast, this area of our country is very vulnerable to severe damage from waves. Firstly because hurricanes formed in the northern hemisphere originate at tropical and subtropical latitudes and then tend to make their path toward the west-northwest as directed by east-to-west tradewinds. Secondly, the Gulf stream runs along the East Coast with warm water from the tropics, which is perfect for hurricanes to fester and survive. Hurricanes in the area of Folly Beach tend to occur during the months of July through October, and northeasters, which also affect this location, take place from October through April (NOAA 1979).
The occurrence of continuous storms in the 1930s, 1940s, and 1950s caused property and infrastructure loss (Dean, 1999). Between 1950 and 2004, there have been 20 tropical storms (Figure 2), averaging one storm every two years (Levine et al, 2009). The most devastating storm to impact Folly Beach was Hurricane Hugo in 1989. This hurricane landed north of Charleston, and its southern part originated record storm surges of ~6 m along parts of the South Carolina coast including Folly Beach (USDOC, 1990). An example of the damage caused by the storm is the severe erosion of the beach and dune system, where much of the protective primary and some secondary dunes washed away and moved to the upper beach level (Stauble et al, 1991).
Another factor contributing to Folly Beach’s erosion is sea level rise. Data from the Permanent Service for Mean Sea Level housed within the National Oceanography Centre in Liverpool (U.K.) determines Charleston Harbor’s local Sea Level Rise to be a total of 3.46 in (~88 mm) in records from ~1980 to 2010 (Kana et al, 2013). However, as climate change continues, sea level around the world continues to rise. In part because of the water added to the ocean through ice-sheet melting, and also because warmer water temperature means water expansion, as warm water takes up more space than cold water. South Carolina’s shoreline has already migrated landwards in response to the rise in sea level (W.C. Schwab). Folly Beach is endangered not only because its maximum elevation is 6.2 m, making flooding considerably easier (Hippensteel, 2008) but the shore is also rather flat and very gently sloped, so the smallest rise in sea level can flood large areas of land (Levine et al, 2009). There has already been an increase in Folly Beach’s coastal flooding days as a result of climate change (Figure 3).
The global sea level has been recorded to increase at an average rate of ~2 mm per year during the 19th and 20th centuries (Douglas, 1997). However, records from Charleston estimate a rise of 3.28 mm per year, a rate considerably higher-- as the sea level continues to rise gradually, waves and currents will inundate low-lying coastal areas, causing Folly Beach to continue migrating landward (W.C. Schwab).
The constant retreat of Folly Beach has put pressure to deploy protective measures in order to slow down erosion and protect the city’s infrastructure. The first attempts at this took place in the 1940s, about 10 years after erosion started to become visible as a result of the Charleston Harbor jetties (FBR, 2014). Groins of large rocks were set at the shore, destroyed by Hurricane Hugo in 1989, and replaced soon after-- but the shoreline continues to erode at a rate of around 4 to 6 feet per year (FBR, 2014). NOAA’s “South Carolina Survey Report on Beach Erosion Control & Hurricane Protection” (1979) reads in regard to hard structures of this type: “These structures have at best resulted in a temporary solution to the problem they were meant to solve; however, the erosion of the beach strand and berm goes on, often at an accelerated rate because of the reflective nature of corrective structures.” The city now employs “soft” methods of stabilization, mainly beach renourishment (Levine et al, 2009). However, this method is extremely expensive and seems to be an ultimately futile short-term solution to a long-term problem as proved by the processes and outcomes of the several renourishment programs implemented over the years.
After the devastation caused by Hurricane Hugo, the federal government authorized Folly Beach’s 1993 restoration project (Gayes et al., 1998) and agreed to cover 85% of the cost (NOAA, 2008). The first several projects took place that same year, yet two-thirds of the newly introduced sand washed away by 1995 (FBR, 2014). Folly Beach County Park south of Folly Beach, for example, eroded severely due to storms while it received the dredged sand from the Folly River and the adjacent Stono Inlet during the 1993 project (NOAA, 2008), and the U.S. Army Corps of Engineers spent $315,000 to pump ~68,809 m3 of sand to the park site. Later, in 1998, emergency renourishment for the park was needed (Gayes et al., 1998). This project cost $100,000 and was completed in 1998 (Levine et al, 2019). The exact quantity of sand used during these renourishment projects was dependent on the existing beach profile at the time of construction, but it is estimated that 1.5 million cubic meters of sand have been delivered to the beach (POCofC, 2008). In addition, another 37,463 cubic meters of transported sand was necessary for 1999 due to continued erosion which caused additional damage to the park’s infrastructure and cost $228,000 federal dollars (POCofC, 2008).
Folly Beach saw 5 storms during the 2004 hurricane season: Alex, Charley, Frances, Gaston, and Jeanne, and several other strong nor’easter storms affected South Carolina’s coast between July and September of 2004 (Levine et al, 2009). This series of storms once again eroded the beach’s shoreline, threatened infrastructure, and led to another renourishment project in 2005. This project placed sand from an offshore borrow area onto the beachfront and cost $12,500,000 (SCDHEC). Unfortunately, after Folly Island completed the 2005 renourishment project, two tropical storms (Ophelia and Tammy) struck and eroded the beach (Eiser, 2006). Ophelia washed away approximately the same amount of sand that had been previously transported during renourishment.
Each subsequent renourishment project has been eroded by storms and the lack of sediment supply caused by the jetties’ interference. While replenishing sand does keep the beaches from being eroded away quickly, erosion proves inevitable. Every time a powerful storm hits the South Carolina coast, sand is swept away from its place – in Folly Beach’s case, sand that cost millions of dollars to put there. Gayes said that since the first re-nourishment project in 1993, the process of combating erosion on this beach has cost around half a billion dollars.
Folly Beach is a quickly eroding Island on the coast of South Carolina. Most of the long-term erosion comes from the jetties on the mouth of Charleston Harbor, which starve the beach from sediment deposition coming from the south-flowing longshore current. There have been continuous attempts to maintain the beach since the 1930s by renourishment, however, the beach continues to retreat and the common storms exacerbate this problem. Although these methods might keep the shoreline somewhat stable for now, “without changing the environmental conditions that caused the Folly Island to erode, the beach will need to undergo repeated, future renourishment projects” (Levine et al, 2009). These projects are very expensive and ultimately pointless. Unless the jetties are removed, Folly Beach with continues to erode indefinitely, even though humans will preserve its shoreline.
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