Date of Award

Spring 2017

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Larry G Ward

Second Advisor

Joel E Johnson

Third Advisor

Thomas C Lippmann

Abstract

Coastal systems worldwide are undergoing increasing pressure as a result of growing anthropogenic influences, accelerated eustatic sea-level rise, and more intense storms due to climate change. Beaches in New Hampshire have not been systematically studied to assess seasonal changes in beach morphology, erosional and accretional trends, controls on beach processes, or the impact of climate change. In order to further the understanding of a highly-engineered, paraglacial, bedrock-influenced coastal system, six major New Hampshire beaches were monitored from July 2015 to August 2016 for changes in beach morphology and sediment volume. A GNSS rover beach profiling system was utilized to measure beach profiles. Post-processing of the GNSS data revealed that the paths of the profiles often deviated from a shore-perpendicular line. Therefore, a novel processing method was developed to correct and interpolate the profiles to shore-perpendicular lines for comparison. In addition, sediment samples were collected on the upper, middle, and lower beach during summer 2015 to characterize the beaches. Seasonal changes in beach morphology, in addition to sediment grain size distribution, were utilized to classify the beaches and provide insights into beach behavior and possible controls.

Overall, the three northern beaches (Wallis Sands, Foss Beach, and Jenness Beach) are bimodal, granular to pebbly fine to medium sand, dissipative beaches. These beaches tend to be narrow, flat, and featureless welded barriers bounded by bedrock headlands or glacial deposits. The northern beaches tended to undergo vertical erosion and accretion on the scale of weeks to months across the entire width of the beach. Two of the three northern beaches had stations that underwent major net sediment volume changes over the study period. For example, a station on Foss Beach accreted up to an average of 0.87m3 per meter of beach width, while a station on Jenness Beach eroded an average 0.59m3 per meter of beach width. The southern three beaches (North Hampton Beach, Hampton Beach, and Seabrook Beach) are unimodal, granular to pebbly medium to coarse sand, intermediate to reflective beaches. The southern beaches are wide barriers with well-developed berms and large sediment volumes. These beaches tended to undergo major erosion and accretion of the berm, including berm crest retreat/advance on the scale of weeks to months. The southern beaches generally ended the study period with negative net sediment volume change (0.2-0.6m3 eroded per meter of beach width, with a maximum of 0.67m3 eroded per meter of beach width at southern Seabrook Beach). The results of this study suggest that New Hampshire beaches are vulnerable to erosion under current and future threats of sea-level rise and more intense storms related to climate change.

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