Beach Building In South Carolina – By Natural Processes – Coastal Science & Engineering

By Timothy W Kana PhD

Kiawah Island’s famed Ocean Course will be the site of the 2012 PGA championship in August.  Without question, what makes the course special is its setting along the spectacular oceanfront.  The course runs between windswept dunes and freshwater ponds at the eastern end of the island―amazingly, on land that did not exist a century ago.

The geologically young dunes and ponds of Kiawah Island owe their existence to a natural process that is common to most South Carolina barrier islands.  In fact, were it not for this phenomenon, our beaches would not be as healthy and valuable.

The little known secret of the South Carolina coast is that it has a plentiful sand supply in many places―so plentiful, that numerous beaches have built seaward throughout the 20^th century despite sea-level rise and the impacts of storms.  Through a combination of forces unlike those controlling most East Coast beaches, the SC coast has numerous inlets and exceptionally large underwater deltas at their entrances.  Boaters know these shoals as the bar that has to be crossed on the way to offshore fishing grounds.  The phenomenon that accounts for accreted land on which the Ocean Course sits is referred to by professionals as “bypassing”―the term simply describing the movement of sand across an inlet from one beach to another.

It is easy to visualize sand being carried by waves along Myrtle Beach during a northeaster, then bouncing across – that is, bypassing – Withers Swash, a small inlet that people wade at low tide.  But the eastern end of Kiawah Island is flanked by Stono Inlet, one of the largest and deepest entrances on the East Coast.  So much water passes through Stono Inlet with each tide that its channels and deltas extend miles offshore.  Researchers at the University of South Carolina –USC– estimate Stono Inlet shoals contain enough sand to create another Kiawah Island 10 miles long and 1 mile wide with left-over volumes.  What makes Kiawah healthy is the fact that every five years or so a large mass of sand shifts from the Stono Inlet shoals to the east end of the island.

It is impossible for sand to simply hop across huge Stono Inlet from Folly Beach to Kiawah.  But some sand from the “Edge of America” has found its way to Kiawah over time.

For a bucket of sand from Folly Beach County Park to reach Kiawah’s Ocean Course beach about 8,000 feet away, it will spend decades falling into Stono Inlet channels, then getting flushed to the outer reaches of the delta, only to be pushed back shoreward by waves, deposited temporarily on low “bird” islands, washed back into channels, and once again shifted to the outer bar.  After such exhaustive travel and with luck, a bucket’s worth of sand―the original bucket is now dispersed over a wide area―will end up in a shoal off the Ocean Course.  And this is where it gets interesting.

Shoals off the Kiawah side of Stono Inlet hover offshore for several years, building volume and gaining elevation.  Then some event such as a storm or a change in channel alignment will separate the shoal from the rest of the delta and set it in motion.  Waves will break over the bar and push sand toward the beach.  As this happens, the receiving shoreline goes crazy.  The section of beach in the lee of the bar builds out to meet the incoming shoal―sometimes by over 1000 feet.  Meanwhile, beaches at the flanks of the incoming shoal erode rapidly.  Finally, the shoal merges with the beach, and spreads in either direction.  In the extreme, the shoreline may jump over a quarter mile seaward, leaving a sheltered lagoon between the original dune line and the new beach.  This is how Kiawah’s eastern end got its numerous ponds, which now provide great habitat for shore birds as well as hazards for golfers.

Episodic bypassing like this has kept Kiawah flush with sand for centuries.  Similar events caused $500 million worth of property at Isle of Palms to be undermined by the surf in 2007 while a shoal-bypassing event played out.  Recent episodes at Kiawah involved so much sand that a new barrier beach and lagoon three miles long formed around the eastern end of the island.  Situated as it is at the western flank of the new beach, the Ocean Course nearly lost its 18^th fairway in 2006 as the shoal was moving onshore.  The beach at the driving range eroded 700 feet in three years.  Some who regularly play the course may have seen earthmovers straightening the beach and realigning channels that flush the new lagoon.  With a month or so of effort in 2006, the 18^th fairway was spared further erosion.  All signs of manipulation of the beach are long gone, and the course remains championship caliber safely behind new dunes.

We know much more how the South Carolina coast evolves thanks to 40 years of studies at Kiawah Island, which began under the direction of Professor Miles Hayes at USC.  Hayes, the premier coastal geomorphologist in the US, coined the term “drumstick barrier island” which at once evokes the shape―likened to a chicken drumstick―of many South Carolina islands and explains how inlets supply sand to our beaches.  As he supervised over 70 Masters and PhDs during his career, Hayes continually reminded us that the coast, as we know it, exists in a balance between the rate of sea-level rise and the rate of sediment supply.  Places like Kiawah Island, Isle of Palms, and Sullivan’s Island―to name a few developed South Carolina islands―have healthy sand supplies and beaches that have more than kept pace with the rising sea.  In fact, an issue for some property owners today is the wide expanse of mature vegetation that is taking over the dunes in accreted areas―this despite a one-foot rise in sea level in Charleston since 1900.

Additions of sand to SC beaches, whether by nature or by artificial nourishment, have saved golf courses like Kiawah’s Ocean Course and Wild Dunes’ Links Course, and have enhanced property values from North Myrtle Beach to Hilton Head Island.  Additions of sand have increased the separation between houses and the surf, lessening the damaging impacts of storms.  Artificial additions of sand in some places have cost millions of dollars, but more often than not, have added many times their cost in higher property values within the beach community.

When the PGA comes to South Carolina in August, think about the sweep of dunes and fairways that now lie where waves broke not too long ago.  This vista may be not-sustainable over geologic time scales, but I would bet it can be with us for several more generations.

 Dr. Kana is founder and president of Coastal Science & Engineering Inc based in Columbia, South Carolina, and is a graduate of The Johns Hopkins University and University of South Carolina.  He is author of Coastal Erosion and Solutions ― A Primer ― available online at www.coastalscience.com.

FIGURE A.   Eastern end of Kiawah Island looking southwest in April 2011.  The shoreline has jumped seaward numerous times since the 1860s by massive releases of sand from Stono Inlet (foreground).

FIGURE B.   The Ocean Course lost 700 feet of dunes between 2003 and 2006.  Trucks and bulldozers restored the area and prevented loss of the 18^th fairway in 2006.  Photos ©Coastal Science & Engineering Inc.