Paper No. 7
Presentation Time: 9:50 AM
BARRIER ISLAND GENESIS AND BEACH SCRAPING IN MAINE: ACCELERATING COASTAL PROCESSES
A decade of unprecedented beach and dune erosion at Popham Beach in Phippsburg resulted from the interplay of tidal inlet migration, barrier spit extension, spit and tombolo breaching, and shifting back-barrier tidal exchange through competing inlets. A state park bath house was planned to be sited behind 400 feet of dunes in 2007. By November 2009 when construction was completed, erosion extended into a back-dune pitch pine forest with only 100 feet to the shore. At our recommendation, tree wattles were built in December 2009 from fallen pines to slow tidal channel erosion in front of the bath house. In March 2010 the Morse River cut a direct channel to the sea and created a barrier island offshore of the park. The tree wattle became buried in a growing dune for a year and then was exhumed by channel erosion forced by landward barrier island migration. With regular monitoring and just 25 feet between the bath house and the ocean after Hurricane Irene (August 29, 2011), we designed beach scraping that moved 10,000 cubic yards landward and filled in the tidal channel, buried the wattles, and built a dissipative beach in December 2011. Scraping mimicked spit migration and left critical piping plover habitat undisturbed for spring. Within weeks, a new tidal inlet formed farther seaward and the loss of the bath house and adjacent leach field were averted. To further complicate the shoreline response, an adjacent tombolo breach inhibited onshore bar migration in a downdrift section of beach and led to drift reversal, over 100 feet of dune loss in 3 years, exhumed buried seawalls, and transgressed a beach to within 50 feet of the only road that is access to a peninsula. The scale of beach and dune dynamics experienced in the last decade has surpassed that which could be predicted based on the 20th century. In the last 5 years, sea levels have been higher than in recent decades and the barrier island formed during a winter of unusually high sea levels and a week of Perigean storm tides and high surf. A thorough understanding of coastal processes, shoreline migration, and sand budgets are essential to coping with unforeseen consequences, preserving the natural integrity of coastal ecosystems, and protecting the built environment.