Far from shore, in the deep ocean, winds blow over the surface of the water and create waves. Barrier islands buffer our coastline from the ocean's wave and storm energies. Beaches absorb and dissipate these immense forces, but offer little resistance to them. Along the eastern seaboard, storms often are concentrated in specific seasons. Storms are especially frequent during the winter months and hurricanes occur in the late summer and early fall. Our beach sand responds to these seasonal trends by varying between the winter "eroding" profile and the summer "building,"or accretional profile (www-class.unl.edu, 2001).

In the summer months when storms are small (with the exception of occasional hurricanes), it is normal for beaches to grow larger in width. Sand accretes onto the beach from the offshore zone (particularly from sandbars) by the onshore swash which carries sand and water onto the beach. Since the water is absorbed by the beach and the sand is deposited, the backwash flow is almost eliminated. This reduces the amount of sand flowing back into the ocean. At this time when sea levels are at their normal lows, wind picks up sand from the dunes and blows it onto the beach. The net result from both processes of sand relocation allows the island to grow seaward during the summer.

The most dramatic short-term changes of a barrier island occur during the winter months and during large storm events (like summer hurricanes). Sporadic in nature, storms are the primary cause of beach erosion along many coasts. Storm surges deliver large volumes of water and sediment onshore. When the beach sand becomes saturated, the sand can no longer store the water and the water flowing up on the beach also flows back into the ocean. If the backwash has enough energy, it will erode the beach's sand and transport it offshore. It is important to remember, sand from the dunes is also being carried offshore during these storm events.

During winter storms, islands migrate landward due to rising sea-levels and predominant winds from the northeast. The greater strength of winter winds (called "Nor' Easters") cause dunes to migrate to the southwest. Large quantities of sand are carried to the island's backside by the overwash of the sea. As we learned earlier (for review click here), rollover exposes the shoreline's old layers of shells and peat (from the marsh) that are ancient sediments of barrier islands.

Hurricanes are large storm events that are associated with high winds, heavy rains, and storm tides. Tidal flooding and highly erosive storm surges are two of the most devastating effects of hurricanes. In South Carolina, these storms are the most common and the most damaging natural disaster we face.

During the months of August, September, and October, tropical cyclones (hurricanes) develop in the Atlantic, the Caribbean, and the Gulf of Mexico. These develop when wind speeds change from low to high, coupled with water temperatures above 80 degrees Farhenheit. Trade winds begin to circle around areas of low pressure and a hurricane is born. These cyclones have wind speeds of up to 74 miles per hour and can reach widths of fifty to one thousand miles in diameter (OCRM, 2000).

South Carolina is no stranger to hurricanes. Our most damaging hurricanes struck landfall in 1752, 1885, 1893, 1911, 1940, 1959 and 1989 (OCRM, 2000). Although meterologists predict approximately four hurricanes each season to strike the eastern and southern U.S., Hurricane Hugo is probably the most memorable hurricane within the last two decades for South Carolinians (OCRM, 2000).

On September 21, 1989, Hugo hit the U.S. mainland just north of Charleston, South Carolina, costing $5.9 billion in damage and the lives of 29 people (OCRM, 2000). This is one of the U.S.'s most expensive hurricane disasters in history. Sustained winds of 215 kilometers per hour (or 134 miles per hour) were recorded and a storm surge of more than 6 meters battered through our coast. McClellanville, a small fishing town just north of Hugo's landfall, was covered by a blanket of water more than 19 feet tall at the time of high tide (OCRM, 2000).

Considering that South Carolina's barrier islands are less than 3 meters above sea level, they were completely inundated by the large storm surge. In certain areas along our coast, beaches were severely eroded and dunes were leveled. The immense storm surge removed sand from the beaches and dunes and deposited it on the backside of the island (as overwash), or carried it offshore.

The lesson Hugo taught South Carolinians and coastal communities around the world was the importance of wide, high beaches and sand dunes for natural protection, and the need for good construction methods. Even though Folly Beach did not experience the most intense effects of the hurricane, the erosional effects along its shore were obvious.

Since the 1930's, Folly has experienced severe erosion and attempted to armor the shoreline with boulders and rubble to stabilize the sand. These strategies were no match for Hugo. Folly suffered major damage (or complete loss) to beachfront property due to the storm surge of over 3.5 meters (20 feet) above mean sea level (OCRM, 2000). Isle of Palms and Sullivans Island, just north of Charleston, experienced considerable damage. However, wider beaches, healthier dune systems, and better-constructed housing minimized the effects on these islands compared to the lower standards of shoreline development and policies on Folly Island.

"The Dynamic Beach" (by Betsy Sheffield) is a beach profiling activity that produces accurate results without expensive equipment. This document is written in PDF format and requires Adobe Acrobat Reader. To download this free software, click on the Adobe button. NOTE: This activity is correlated to the S.C. Science Curriculum Standards