A REVIEW OF SEDIMENT BUDGET ESTIMATIONS
AT FIRE ISLAND NATIONAL SEASHORE, NEW YORK

Technical Report NPS/NER/NRTR--2008/114

Erika E. Lentz¹, Cheryl J. Hapke², and William C. Schwab<sup>3

1</sup>Department of Geosciences
University of Rhode Island
Kingston, RI 02881

²U.S. Geological Survey, Coastal Field Station
Department of Geosciences
University of Rhode Island
Kingston, RI 02881

³U.S. Geological Survey, Woods Hole Science Center
384 Woods Hole Rd.
Woods Hole, MA 02543

March 2008

U.S. Department of the Interior
National Park Service
Northeast Region
Boston, Massachusetts

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Executive Summary

This report presents a review of the existing body of scientific literature, as it pertains to issues relevant to coastal sediment budgets, both at Fire Island National Seashore (FIIS) and in general, in order to provide the National Park Service (NPS) with the information they need to best manage park resources at FIIS. The review outlines the state of knowledge on processes of sediment transport, and addresses the relationship of the nearshore with the shoreface and beach. Few studies of sediment budget processes exist for Fire Island and the south shore of Long Island, and as such, this review includes the current knowledge base of studies conducted worldwide.

Due to the large potential uncertainties associated with calculating sediment budgets, they are inherently difficult to quantify. A number of detailed estimates of sediment budgets exist for Fire Island and the entire south shore of Long Island. However, very few of these have been published in the peer-reviewed literature or as gray literature (e.g., conference proceedings, Ph.D. theses). For the purposes of this report, we are only citing the aforementioned body of literature and are not considering agency technical or administative reports in the review. This is not to discount the integrity of these reports; instead it is to assure that the science we are summarizing for the NPS has passed through the peer-review process that is standard for scientific advancement of information and ideas.

A variety of beach nourishment projects have been conducted over the last 50 years to mitigate coastal erosion for privately owned lands on Fire Island, a partially developed barrier island along the south shore of Long Island, New York. The inner continental shelf closest to the project sites has typically been the source of the nourishment material. Additional nourishment projects are being planned and more are anticipated in order to protect property and development from predicted sea-level rise and increased storminess due to climate warming. Currently proposed dredging areas are located in inner shelf and nearshore regions immediately adjacent to the boundary of Fire Island National Seashore (FIIS). Removal of sediment from nearshore regions has the potential to alter wave refraction and diffraction patterns, and result in changes in the wave energy reaching the beach.

Sediment budget assessments for the Long Island south shore, which have been estimated over a variety of timescales, document variable volumes of littoral transport, with the primary component being longshore transport from east to west. However, published sediment budgets indicate that an addition of approximately 200,000 m³/yr of sediment is needed to account for the calculated longshore transport volumes for the coastal system. The source of additional sediment has not been unequivocally identified, although geophysical mapping and sediment analyses suggest that a series of shoreface-attached sand ridges could be a conduit for the onshore transport of inner shelf sediment to the system. There is a growing body of literature that documents the contribution of inner shelf sediments to sediment budget estimates of coastal areas, though little data exist on this subject at Fire Island. However, results of shelf mapping, beach profile comparisons, and sediment budget calculations indicate that onshore sediment transport at Fire Island is likely an important process, on time scales ranging from single storms to decades and longer.

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