Date of Award

Fall 2015

Document Type

Thesis

Degree Name

Master of Science in Environmental Science - (M.S.)

Department

Chemistry and Environmental Science

First Advisor

Nancy L. Jackson

Second Advisor

Karl F. Nordstrom

Third Advisor

Zeyuan Qiu

Abstract

Sandy backshore enclaves are created where shorefront buildings are lost during high magnitude storms. Subsequent foredune growth in these enclaves is critical to providing protection to landward development. Conditions for foredune growth and sediment flux within an enclave can be influenced by the presence of adjacent buildings. The objectives of this research are to assess the following questions: what is the nature of sediment flux on a beach within an enclave, what are the potential constraints to transport on a beach within an enclave and, are natural processes alone able to sustain a foredune in an enclave. A field investigation was conducted within an enclave in Bay Head, NJ between 02 November and 25 December 2014. Four events were monitored during strong winds to assess wind characteristics and sediment transport across the Dune, Backshore and Foreshore.

Wind characteristics were measured using three anemometer towers each with four or five anemometers deployed at the Dune Crest, Dune Toe and Berm Crest. Total transport rates were measured using cylindrical traps emplaced during high wind events on 02 November, 18 November, 07 December and 25 December. Surface sediment moisture, grain size, fetch distance and topography were measured to assess potential constraints to transport.

Dominant direction of regional winds are WNW, but were NNW at the study site during the field investigation. The highest wind speeds and sediment transport rates occurred at the Berm Crest during alongshore winds when fetch distances were greatest. Average wind speed of 7.67 m s-1 resulted in a trapping rate of 21.32 kg m-1 ht-1 at the Berm Crest but trapping rates were an order of magnitude lower at the Dune Toe and Crest where average wind speeds were 6.26 and 5.62 m s-1.

Sediment moisture content across the Dune and Backshore ranged from 0.0 to 4.6% during the four events. Fetch distances, ranged from 5 to 64m within the enclave and 61 to 65m at the Berm Crest. Fetch distance was limited by a sand-trapping fence at the Dune Toe and a house with perimeter sand-trapping fence located to the north. The longer fetch length at the Berm Crest was due to its seaward location relative to the house to the north. Overall average wind speeds and trapping rates were reduced during offshore winds.

Unsteady, low wind speeds within the enclave reduced the potential for sediment transport near the Dune Toe. The average grain size of surface sediment (0.68) mm and average fetch length (39 m) also contributed to lower aeolian sediment transport within the enclave. These results suggest that foredune growth within an enclave may require human intervention to reach adequate size for shore protection.

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