The Ever Changing Barrier Islands

By Troy Gilbert

Photo of pine trees on Horn Island

The barrier islands of Mississippi are an important first line of hurricane defense and often bear the full force of such storms. Subjected to these extreme weather events throughout their estimated 4,500-year history, these sandy, narrow spits of land paralleling the coast act as speed bumps for storm surge and protect the developed coastline. There were natural processes in place to replenish and repair damage, but in the last 50 years giant swaths have been carved out of the islands and erosion is now systemic with loss rates dramatically accelerating in the last few decades due to human activity.

In the 1960s, Hurricanes Betsy and Camille pounded the Mississippi coast, splitting Ship Island in half and creating what is now known as Camille Cut, as well as East and West Ship Islands. Hurricane Katrina further enlarged the Camille Cut and reopened a wide pass into the western side of Alabama's Dauphin Island in 2005. This cut into Dauphin Island occurred during several other major storms — Petit Bois Island broke off Dauphin Island in the 18th century — yet Alabama's largest barrier island is the only one in the chain still experiencing natural sand rejuvenation. While federally protected to varying degrees since 1971, the issue hasn't been development pressures on Mississippi's barrier islands, but the dredging and deepening of shipping channels through the relatively shallow Mississippi Sound and into the waters of the Gulf of Mexico.

Constantly in a state of flux as they shift and move westward at up to 130 feet a year with the prevailing current and winds, their sands have historically and naturally eroded from the eastern islands and migrated to the west. This system tends to create shoaling and even periodic islands appearing where before there were none. In 1917, a small island emerged in between Horn and Ship Islands and by the mid-1920's had been developed into a resort and casino during prohibition. Due to natural erosion patterns, by 1932 it and all developments on the island had washed away.

With the dredging of these channels to increasingly greater depths to accommodate modern shipping, the natural repair mechanisms have failed. The replenishing sand in the water column is grabbed by these channels, which act as "sand sinks" and have contributed to the dramatically increased speed of erosion. According to the U.S. Geological Survey, Petit Bois Island has shrunk by 50 percent and Ship Island has lost nearly 65 percent of its landmass since 1917, and the loss has accelerated in direct proportion to the widening and deepening of these channels. Relatively, Horn and Cat Island have tended to be the most stable but are not immune. While the growing frequency of intense hurricanes and the normal issue of cold fronts stirring up the shallow Mississippi Sound contribute to the erosion and narrowing of these islands, sometimes dramatically, the one manageable issue is the need for proper placement of beach-quality dredge back into the water transport system or directly onto the islands themselves.

Placement of sand removed directly from dredging has occurred on Ship Island periodically, to protect the historic Fort Massachusetts. In 2009, the U.S. Army Corps of Engineers proposed a nearly $500 million plan to re-nourish Petit Bois and Horn, and the closure of the 3-mile-wide Camille Cut in Ship Island. The first phase of this work was completed in 2011 with the reconstruction of nearly 300 feet of the northern beaches of West Ship Island. The second phase, which includes the massive project of closing the Camille Cut, is expected to begin in 2014.

"For decades, we had a limited understanding of barrier island systems," says Dan Brown, park superintendent for the Gulf Islands National Seashore. "It wasn't until researchers started documenting and correlating the deepening of these channels to their land loss that we began to understand what was happening."

Further studies are underway by the Army Corps of Engineers as to how to best directly infuse beach-quality sand into the water column's sand transport system from the routine dredging of these shipping channels. The importance of these barrier islands in defending the coast's ports, oil and gas infrastructure, and residents from storms is a perfect example of economic and environmental interests walking hand in hand. 

— Published: June/July 2014

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