Identification and classification of very low frequency waves on a coral reef flat

Journal of Geophysical Research C: Oceans
By: , and 

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Abstract

Very low frequency (VLF, 0.001–0.005 Hz) waves are important drivers of flooding of low-lying coral reef-islands. In particular, VLF wave resonance is known to drive large wave runup and subsequent overwash. Using a 5 month data set of water levels and waves collected along a cross-reef transect on Roi-Namur Island in the Republic of the Marshall Islands, the observed VLF motions were categorized into four different classes: (1) resonant, (2) (nonresonant) standing, (3) progressive-growing, and (4) progressive-dissipative waves. Each VLF class is set by the reef flat water depth and, in the case of resonance, the incident-band offshore wave period. Using an improved method to identify VLF wave resonance, we find that VLF wave resonance caused prolonged (∼0.5–6.0 h), large-amplitude water surface oscillations at the inner reef flat ranging in wave height from 0.14 to 0.83 m. It was induced by relatively long-period, grouped, incident-band waves, and occurred under both storm and nonstorm conditions. Moreover, observed resonant VLF waves had nonlinear, bore-like wave shapes, which likely have a larger impact on the shoreline than regular, sinusoidal waveforms. As an alternative technique to the commonly used Fast Fourier Transformation, we propose the Hilbert-Huang Transformation that is more computationally expensive but can capture the wave shape more accurately. This research demonstrates that understanding VLF waves on reef flats is important for evaluating coastal flooding hazards.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Identification and classification of very low frequency waves on a coral reef flat
Series title Journal of Geophysical Research C: Oceans
DOI 10.1002/2016JC011834
Volume 121
Issue 10
Year Published 2016
Language English
Publisher American Geophysical Union
Contributing office(s) Pacific Coastal and Marine Science Center
Description 15 p.
First page 7560
Last page 7574
Country Republic of the Marshall Islands
Other Geospatial Roi-Namur Island
Online Only (Y/N) N
Additional Online Files (Y/N) N