Date of Graduation

Spring 5-2013

Level of Access

Open Access

Degree Name

Bachelor of Science

Department or Program

Geology

Second Department or Program

Art and Visual Culture

Number of Pages

107

First Advisor

Michael Retelle

Abstract

The Popham-Seawall complex, located at the mouth of the Kennebec River in Phippsburg, mid coast Maine, is a dynamic, transgressive barrier beach system. In recent years, the migration of two main tidal inlets in the barrier system has played a major role in increased beach erosion at Popham Beach State Park and on the pocket beaches of Cape Small. Changes in the Seawall barrier in recent years have been minimal, however since 2010, landward recession of the frontal dune ridge has become apparent. The purpose of this study is to document physical changes along the barrier complex, pocket beaches and associated tidal inlets, from summer 2012 through winter 2013, and compare the influence of storm events and seasonal weather patterns on the geomorphology of the entire complex. Detailed seasonal and storm-induced changes on the beach system were documented by topographic profile survey, high resolution GPS tracks, and net sand migration analysis. Longer term (annual) changes were documented using high resolution georeferenced satellite imagery and air photographs. Beach front at Popham Beach State Park has undergone sustained, documented erosion since 2007 when the Morse River migrated towards State Park beaches with the eastward longshore growth of the Seawall Barrier spit. Although the long Seawall spit was breached by avulsion of the Morse River in 2010, erosion has continued along the beach front. Analysis of the net sediment transport shows extensive erosion as summer transitions into fall, with 1763m3 of net sand loss to the West Bath House shore front. Likewise, pocket beaches at Cape Small are continually eroded by the westward shift of the Sprague River, forced against the Cape Small headland by the westward development of the southwestern Seawall spit. Recent changes in the 2.25 km-long Seawall barrier beach are evident with up to 15m of landward migration of the frontal dune ridge in many sectors of the beach since 2009. As a result of Hurricane Sandy and the winter storm Athena, beginning on October 28th and November 7th respectively, enhanced longshore sediment transport was documented with 2256 m3 of sand accreting onto the shore face at the W15OO transect, located directly up drift next to the southwestern Seawall spit, indicating continued spit growth via displaced sand.

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