Document Type

Honors Thesis

Publication Date

Spring 5-2017

Abstract

The purpose of this thesis is to evaluate the effectiveness of hard coastal armoring structures and their cumulative effect upon the shape and volume of sediment of the beach profile at which they are implemented. Four coastal sites in Southern Maine were selected for study: Wells Beach, Higgins Beach, Scarborough Beach, and Laudholm Beach. The years 2006 – 2014 were examined for seasonal meteorological, volumetric, and sediment characteristic changes at each location. Profiles established at these beaches are protected by a variety of hard armoring structures, such as jetties, concrete seawalls, and stone revetments. Unarmored profiles on these beaches are also evaluated to compare sediment loss and profile shape due to natural processes and as a direct result of the structure itself.

Primary analysis of volumetric changes in the direction perpendicular to the beach profile is done using the Empirical Orthogonal Eigenfunction (EOF) method. The EOF method establishes a set of modes that account for variances within the profile. These modes can be combined to produce the overall profile shape over a specified time frame. The first mode accounts for the greatest possible variance in profile data, and thus represents the dominant profile of the beach. The second and third modes – which represent bar and berm formation patterns – reveal littoral transport patterns along the profile due to seasonal weather conditions. The Even/Odd method provides a supplementary analysis of the impact hard armoring structures have upon the beach in the direction parallel (cross- shore) to the profile. Volume changes on the updrift and downdrift sides of the structure vary depending upon the type of structure implemented and the direction of longshore transport.

In general, an analysis of erosion and accretion using the EOF and Even/Odd methods reveals that sediment on the majority of beaches in Southern Maine is being transported offshore at a rate faster than it is being replenished. Profile data and meteorological trends examined using the EOF method reveal that vertical seawalls and sloped stone revetments cause significant erosion in the nearshore, creating a channel in the beach face. Deposition of this sediment occurs offshore during the winter months. In some instances, storm bars are formed. However, the majority of hard armoring structures experience sediment transport and deposition farther offshore. This pattern does not occur as prominently on unarmored beaches. Similarly, hard armoring structures interrupt cross-shore sediment transport patterns and cause significant accretion on the updrift side and erosion on the downdrift side during storm events. Skewness calculations support these findings: a negative skew typically characterizes profiles protected by or adjacent to armoring structures, signifying erosive conditions. Natural erosive and depositional environments are preserved at unarmored beaches.

Sea level rise and increases in storm intensity are likely to occur due to climate change in the coming decades. The ultimate effect these changes in weather could have upon patterns of erosion is unknown at this time, but it is assumed that sediment will continue to be transported offshore at rapid rates as wave runup and tidal reaches move farther inland. This thesis briefly touches upon storm classification and its effect upon erosion, as well as climate change predictions that could impact shoreline recession and erosion trends. Shoreline recession is approximated using the Bruun rule.

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