Skip Maine state header navigation
Skip All Navigation
|Home | Contact Us | Publications|
Shoreline Erosion at Western and Ferry Beaches, Scarborough, Maine
A previous Maine Geological Survey (MGS) site of the month from June 2006 (Slovinsky, 2006) provided a brief history of beach erosion at Western Beach, Scarborough. It also summarized some of the impacts of beach nourishment efforts on the size of the beach, the dunes, and bird habitat.
Summarized Nourishment History
In December 2004, the U.S. Army Corps of Engineers dredged 90,000 cubic yards of sediment from the main channel and anchorage area of the Scarborough River, and placed the material at Western Beach as the beneficial reuse of dredged material. The design of the fill was to increase the dry beach width by adding elevation and width to the berm, the relatively flat area between the edge of high water and the dune vegetation line. As a result of the nourishment project, there was an approximate 6-acre gain in the dry beach, and a substantial gain in available habitat for endangered and threatened piping plovers and least terns.
Shoreline Change Analysis
In order to examine shoreline changes of the surveyed vegetation line and the high water line, MGS utilized the USGS Digital Shoreline Analysis System (DSAS) (Thieler and others, 2009). Surveyed positional points were imported into a GIS and converted into line files. Then, the DSAS software extension was used to compare shoreline positions and calculate the net shoreline movement (NSM, in meters) along the beach at designated transect locations at set intervals. This analysis was conducted for Western Beach along the Prouts Neck Country Club, Ferry Beach, and the neighboring beach that fronts Ferry Road.
Shoreline Change Analysis Results
High Water Line changes
For the overall study area, the mean NSM value for the high water line was -8.4 meters, indicating that as a whole, the study area has undergone substantial landward movement of the high water line from 2005-2011, indicative of beach erosion. Based on Figure 2, the high water line along Western Beach has eroded dramatically over this time period, up to 40 meters at its highest point, while accretion has occurred at the point between Ferry and Western Beach, up to about 20 meters.
Vegetation Line changes
Summary of Shoreline Changes and Discussion
Table 1 summarizes the overall mean changes observed in the net shoreline movement of the vegetation line and the high water line for the beach system as a whole, and for each specific section of the beach. Overall, Western and Ferry Beaches are undergoing erosion of the dune and water line. At Western Beach specifically, erosion rates are higher. Along Ferry Beach, which appears to be receiving sediment from an eroding Western Beach, the high water line and dune appear to be growing overall. Along Ferry Road specifically, the mean high water line data indicates general stability, while the vegetation line is showing erosion.
After the beach nourishment that was completed in late 2004 and early 2005, the beaches and dunes at Western Beach grew seaward dramatically. However, since the summer of 2005, the central portion of Western Beach underwent large amounts of erosion, with the dunes losing nearly 20 meters, and the high water line migrating landward upwards of 40 meters from its 2005 position. The changes along this central portion of Western Beach are reflected very well by comparing photographs taken by MGS of the beach and dune from 2005 and 2011. Figure 10 shows the beach and dune in June 2005, with a stake marking the southern limit of the beach nourishment project. Figure 11 shows the beach and dune condition in June 2011 from the same approximate location. The arrows in the photographs are meant to show landmarks (a patch of grass and a low area of the dune crest) which are apparent in both pictures. Note the dramatic loss and lowering of the beach, and the scarping (vertical cutting) of the dune.
From a bird habitat standpoint, Figure 12 shows the changes in bird fencing placed by the Maine Audubon Society from 2005 through 2011. In June of 2005 (blue line) and 2006 (green line), the entire central portion of the beach was fenced for habitat. In the summer of 2007 (purple line), the fencing area decreased on its northern side. No data was collected in 2008, but by 2009 (red line), the fencing was concentrated at the southeastern end of the beach. By the summer of 2010, the fenced habitat was decreased to a small section in the central portion of the beach, and around the point along the Ferry Beach side. In 2011, only a small section near the northern end of the beach, at the point, was fenced for bird habitat. It is clear that the amount of available bird habitat has decreased substantially as the beach has eroded.
Shoreline change analysis indicates that Western Beach has seen some of the worst erosion in the state over the past 6 years. Erosion has moved the shoreline to near where it was pre-nourishment, resulting in loss of the dry beach, and bird habitat that had existed for several years after the nourishment project. It appears that the erosion of the beach and dunes along the central portion of Western Beach is providing sand for substantial spit and dune growth near the point and around the corner at Ferry Beach. This is likely a result of flooding tidal currents that dominate the Scarborough River that pull sediment around the point and into the river, coupled with episodic storm erosion at Western Beach.
Along Ferry Beach, shoreline change analysis showed marked progradation of the dune and beach near the entrance to the river. Along the park, most of the dune also grew, though the high water line migrated landward, for the most part. This decreased the recreational beach space along the park. Along Ferry Road specifically, dune and beach erosion is occurring along the southeastern section, with sand migration to the northwest, with dune and beach growth nearest the homes along the road over the time period monitored.
Beach and dune accretion was concentrated near the point and around the corner, at Ferry Beach. This accretion is likely driven by erosion of the central portion of Western Beach, and subsequent sediment migration due to tidal currents to the northwestern end of Western Beach and to a portion of Ferry Beach. Additionally, beach and dune growth was noted in front of the homes at the northwestern end of Ferry Road.
This type of shoreline change analysis can help determine erosion and accretion patterns along the beach, which in turn, helps determine expected future nourishment lifetimes at Western Beach. It also can be used to help pinpoint where future nourishment may be placed along Western Beach in order to maximize the beach and dune shape, fill lifetime, and hence beach and bird habitat, should a future dredging project occur by the U.S. Army Corps of Engineers.
Slovinsky, P.A., 2006, Beach Nourishment at Western Beach, Scarborough, Maine: Benefits for the Beaches and the Birds: June 2006 Maine Geological Survey Site of the Month.
Thieler, E.R., Himmelstoss, E.A., Zichichi, J.L., and Ergul, Ayhan, 2009, Digital Shoreline Analysis System (DSAS) version 4.0-An ArcGIS extension for calculating shoreline change: U.S. Geological Survey Open-File Report 2008-1278. Available online at http://pubs.usgs.gov/of/2008/1278/. http://woodshole.er.usgs.gov/project-pages/dsas/
Website by Peter A. Slovinsky
Originally published on the web as the August 2011 Site of the Month.
Last updated on August 1, 2011
|Copyright © 2011 All rights reserved.|