MAPPING SEAWALL BEACH TO MODEL FUTURE SEA LEVEL RISE

The coast of Maine and its beaches are threatened by sea level rise from projected climatic warming in the coming century. An understanding of seasonal and long term beach processes is essential for predicting their response to accelerated sea level rise. This study investigates the barrier beach system at Seawall Beach, Phippsburg, Maine over seasonal and longer term periods. The goal is to develop a model for the beach for 2100 A.D. that accommodates various scenarios for projected sea level rise and possible storm surges.

Morphological features on the beach were mapped and monitored between May 2008 and May 2009 in order to understand longer-term development of the barrier system. The modern position of beach features such as the dune front, berm crest, tidal inlets, and sand bar crests were mapped using a high-resolution GPS unit. Seasonal changes of the beach were monitored along five selected transects across the beach to document changes from the summer to winter profiles. Changes in the profiles were correlated to weather data. A time lapse camera was installed in June 2008 to document changes daily on the southwestern spit of the beach. Spatial analysis of short term and long term changes are mapped using ArcGIS. Documentation of the modern “snapshot” of Seawall Beach and the understanding of the beach processes allows more accurate modeling of the future barrier beach system which incorporates various rates of SLR as well as erosion values for the surficial geology, a severe storm zone and slope of the beach.

Six profiles have been collected showing a general trend of summer accretion and the beginning of winter erosion. On December 6th, 2008 dune overwash was observed from a high tide and storm on November 23rd, 2008. The present beach features have been mapped in ArcMap and compared with 2001 and 1953 aerial images and the largest notable changes were with spit accretion on both ends of the beach and river channel migration. A sea level rise range of 0.3-2.12m has been mapped over the beach using 2004 LIDAR data as the basemap and shows a large impact on the southwestern end of the beach and in areas of low lying back marsh.