Date of Award

Winter 2021

Project Type

Thesis

Program or Major

Oceanography

Degree Name

Master of Science

First Advisor

Larry G Ward

Second Advisor

Joel E Johnson

Third Advisor

Thomas C Lippmann

Abstract

Coastal systems are under threat from multiple factors including sea-level rise, climate change, and anthropogenic development. As a result, beach erosion is a major problem along much of the U.S. coastline, including New Hampshire (NH). To combat coastal erosion, engineering solutions such as beach nourishment will likely be utilized. However, to be effective, the natural beach system must be understood. In order to characterize grain size properties, assess sediment sources, and develop conceptual models relating beach morphology, stability, and sediment sources for paraglacial beaches, seven major beaches in NH were studied in 2017. Elevation profiles were measured, and sediment samples collected at twenty-nine shore-perpendicular transects spaced over the seven beaches after an extended erosional period in late winter to early spring and an extended accretional period in late summer. NH beaches can be divided into three groups based on their primary sediment sources which include glacial tills, sandy glacial stratified deposits, and mixed sources (tills and stratified sand and fine gravel). Glacial till sourced beaches (Foss Beach and North Hampton State Beach) tend to have large gravel ramps in the upper beach and are composed of mixed sand and gravel throughout the year. Sandy glacial deposit sourced beaches (Hampton Beach and Seabrook Beach) have higher mean elevations with well-defined berms that remain throughout the year and are composed of coarse to medium sand. The mixed source beaches (Wallis Sands, Jenness Beach, southern North Hampton Beach, and North Beach) tend to have low elevation and build small berms under extended accretional conditions. Mixed source beaches tend to be composed of poorly sorted sand and gravel during the erosional period. However, under extended accretional conditions a sandy accretional wedge is deposited over the erosional surface. Presently, upland sources no longer supply sediment to the beaches north of Great Boars Head (glacial till sourced and mixed source beaches) due to the anthropogenic armoring of the coast in the mid twentieth century. Therefore, the major source of sediment presently is the onshore-offshore movement of reworked offshore deposits. The available sediment in these offshore deposits is relatively minor for most NH beaches. However, Hampton Beach and Seabrook Beach have high volume sand bodies offshore and receive sediment from the eroded sand underlying the back-barrier marsh landward of the beaches. Consequently, the elevation of the beaches north of Great Boars Head is significantly lower than the beaches to the south (sand sourced beaches).

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