Analysis of a 10-Year Record of Nearshore Directional Wave Spectra and Implications to Littoral Processes Research and Engineering Practice

Document Type

Article

Publication Date

9-1-2016

Abstract

Slightly more than 10 years (August 28, 2001, to October 28, 2011) of high-resolution directional wave spectra were measured by an Acoustic Doppler Current Profiler installed in the nearshore at Spessard Holland North Beach Park in Melbourne Beach, Florida. Analysis of the record yields an average wave power of 17.6 MW/m of shoreline but with a standard deviation of 22.5 MW/m. Cumulative annual wave power ranged from 43,455 to 93,722 MWh/m, and the annual storm count was between 3 and 14. The mean spectrum for the entire record shows an almost symmetric directional distribution of wave energy centered on the shore-normal direction, which is somewhat unexpected considering that the net longshore transport in the region is definitively N-S. Partitioning the data into shore-normal, NE, and SE windows shows that most wave energy approaches from the SE, again contrary to expectations. The rigorously integrated mean longshore forcing of wave radiation stress, Sxy, is slightly N-S (7.2 N/m) but has a standard deviation of 77.2 N/m. Computing a cumulative average through the record indicates that it takes between 4 and 5 years for the net magnitude and direction of Sxy to be conclusively revealed. Using significant wave height, peak wave period, and mean wave direction to estimate Sxy yields values nominally 42% greater than the integrated results, confirming that fully directional spectra should be used in both study of littoral processes and coastal engineering practice. Finally, the supposition that the wind plays an important role in driving longshore currents and consequently longshore transport is tested. However, analysis of more than 4 years of wind data collected at the site reveals a mean longshore wind stress that is essentially balanced (i.e. nil).

Publication Title

Journal of Coastal Research

Volume

32

Issue

5

First Page

1162

Last Page

1173

Digital Object Identifier (DOI)

10.2112/JCOASTRES-D-15-00085.1

ISSN

07490208

E-ISSN

15515036

Link to Full Text

Share

COinS