What is Shoreline Engineering?

Working on my research paper, I wrote about shoreline engineering…my examples are from South Carolina. 

Shoreline engineering is man’s way of trying to stabilize the beaches or islands.  Often times, when there is an attempt to correct or stabilize one beach or island, another beach or island suffers.  There are three types of stabilizers used in South Carolina, in addition to beach renourishment, which is the replacement of beach sand by pumping sand in and rebuilding the beaches.  These stabilizers are groins and groin fields, jetties and seawalls. (Neal et al., 1984)

The U.S. Army Corp of Engineers began a beach renourishment program for the mainland coast of South Carolina in 1996 called the Myrtle Beach Shore Protection Project.  Congress approved this fifty-year project in 1990 to provide protection for shoreline property and to provide recreational space on the beaches. (US Army Corps of Engineers, 2010)  The first renourishment project began in 1996.  In two years, more than 6.4 million cubic yards were placed along the Grand Strand costing $51.3 million.  A little over ten years later the second renourishment program was started.  Over an eighteen-month period starting in September 2007, more than three million cubic yards of sand were pumped in from offshore covering approximately twenty-five miles of shoreline from North Myrtle Beach to Garden City Beach costing an estimated $29.5 million.  (US Army Corps of Engineers, 2010)  A study entitled Monitoring Beach Renourishment along the Sediment-Starved Shoreline of the Grand Strand, South Carolina by Coastal Carolina University monitored the beach geodynamics before and after the renourishment to increase their understanding of sediment transport and deposition on a sediment-starved beach.  The study concluded that eroded sands remained within the nearshore sediment area longer than prior to the renourishment and that there was more offshore transport than onshore transport of sand. (Park, Gayes, & Wells, 2009)  The South Carolina code of regulations considers the Grand Strand area the most stable portion of the coast with only one foot of erosion per year. (State of South Carolina, 2010)  Even so, in order to maintain the shoreline of the Grand Strand, beach renourishment will have to continue.

Groins and jetties are walls constructed perpendicular to the shoreline that extend outwards into the ocean.  Their primary function is to catch sand.  Groins are usually smaller in height than jetties and are usually made of stones or wood.  Groin fields are made up of several groins placed strategically along a barrier island.  It is effective with longshore transport in collecting sand between the groins thus fortifying the beach. (Neal et al., 1984) Hilton Head Island has constructed three groin fields and one additional groin along its shoreline.  The north section of the island has seventeen groins adjacent to the Port Royal Sound in hopes of collecting sand and slowing erosion.  The second groin field is located in the center of the island just north of Forest Beach with two groins.  The third groin field has three groins and is located near Braddock Point toward the southern end of the island.  The final groin is located on the southern tip of the island along the Calibogue Sound.  (State of South Carolina, 2010)  Due to the use of groin fields on Hilton Head Island, Daufuskie Island, to its south, is experiencing major loss of it beach due to lack of sand deposition.  In 2009, South Carolina showed the mean erosion rate for Daufuskie Island was over 30 inches per year. (State of South Carolina, 2010)

Jetties are usually built in pairs along shipping channels to keep sand away from the channel or inlet by interrupting the longshore current.  Jetties are parallel to the shoreline and can be rather long.  With the complete blocking of the movement of sand, there is a significant impact on the beaches on either side. (Neal et al., 1984)  A good example of jetties is the Charleston jetties that have been in place since the 1890s.  Although very useful to keep the channel free from sand, Morris Island has been severely affected.  The Morris Island lighthouse was built on the backside of the island in 1876 about 1600 feet from the shoreline.  Due to the lack of sediment supply, the island has eroded and today the lighthouse is completely surrounded by the ocean. (Neal et al., 1984)

Finally, seawalls are massive vertical walls built along the shoreline to protect the backshore from the full force of the tide.  Smaller seawalls are called bulkheads and revetments.  Bulkheads are vertical walls placed in the foreshore of the beach to help stop sediment transport and further erosion from storm waves. (Neal et al., 1984)  Revetments are made of loose stones and are used to protect an area from strong waves by causing the wave to break early and lose some water within the rocks thus losing its strength.  It is effective to control sediment transport as well. (Neal et al., 1984)  There are some problems with seawalls, bulkheads and revetments.  Sediment deposition stops and overtime, the beach below the structures changes its profile and becomes much steeper which increases wave energy.  As wave energy increases, erosion increases until there is no beach left.  New and taller seawalls have to be built every twenty years or so to replace the older one in order to continue to protect structures behind the walls.  (Pilkey & Wright III, 1988)  Folly Island is a good example of an island that uses seawalls.  Almost 60% of the island has seawalls and parts of the beach are completely underwater during high tide. (Pilkey & Wright III, 1988)