Assessing the nature of rip currents along the south shore of Long Island, NY: Dominant rip type and insights into possible forcing mechanisms
Slattery, Michael Patrick
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The south shore of Long Island experiences periodic rip currents that pose a human threat as well as generate scientific intrigue. To address the type of rip currents present along Long Island's south shore, an integrated monitoring system that includes use of beach cameras, the SWAN wave model, and seismic recording stations was implemented. The original site was in East Hampton, NY in a private residence while a second camera was established in the Fire Island lighthouse and a second seismic station was placed in the Maidstone club (also in East Hampton, NY). Statistics from camera observations indicate that rip currents are infrequent appearing less the 1% of the time along the two camera monitored beaches. They are also short in duration, with averages on the order of one minute, narrow, and short in offshore extent. In general, the offshore bar is too far beyond the surf zone to have the usually expected effect on rip current generation, though storm activity may drive rip current events. Instead, rip current traits and lack of dominant bar influence categorize these events as flash rip currents. Seismic signals indicate that there is energy at longer periods affecting our coast. This energy is associated with infragravity waves capable of establishing standing edge waves, one mechanism attributed to rip current formation with the lack of strong bathymetric control. Both seismic stations recorded similar spectral peaks despite there distance of nearly three miles. The only coastal process that should be capable of generating these signals between 4 and 300 seconds are ocean wave fields. No direct measurement of a standing wave was possible, but spectral evidence supports their existence in the nearshore adjacent to our study. The SWAN wave model was limited by accurate, high-resolution bathymetry. While the model accurately depicted incident wave field heights and direction, longer period waves were not able to be modeled. In addition, the resolution was limited to scales approximately the same size as the average rip current making the model unlikely to accurately address flash rips, though it may be suited to fixed rip current studies.