Long-Term Shoreline Change of the Chandeleur Islands Barrier System, Louisiana: 1855 to 1989

The Chandeleur Islands are the largest barrier island system along the Mississippi River delta plain, and are characterized by low-profile, washover-dominated barriers that are rapidly migrating landward. The barrier island system was divided into south and north Chandeleur Islands based on geomorphic characteristics. The south Chandeleur Islands are comprised of Breton, Grand Gosier, and Curlew Islands, while to the north, the islands include Chandeleur, Freemason, New Harbor, and North. The south Chandeleur Islands are fragmented into three groups of small ephemeral islands and shallow shoals separated by wide tidal inlets. The average rate of gulfside shoreline position change averaged -11.6 m/yr between 1869 and 1989, while the bayside rate averaged 10.7 m/yr, causing island width to narrow as the barriers rapidly retreated landward. Average barrier width decreased from 384 to 232 m and area was reduced 44% from 784 to 441 ha for the same time period. The north Chandeleur Islands are dominated by a large, arcuate barrier island system that protects three groups of smaller, irregular-shaped islands that lie to the west in Chandeleur Sound. Between 1855 and 1989, average shoreline movement along the gulf and bay shorelines of Chandeleur Island was -6.5 m/yr and 2.9 m/yr, respectively. The gulf shoreline is migrating landward twice as fast, causing average island width to narrow by 50% (941 to 473 m) for the period of record. Island area decreased 37% from 2,763 to 1,749 ha.