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Keywords:

  • Delaware Bay;
  • estuarine beach;
  • ocean waves;
  • swash bar migration;
  • weather systems

Abstract

A 29-day field investigation was conducted on a meso-tidal sand beach in Delaware Bay, New Jersey to document the contribution of local estuarine and non-local ocean waves to beach recovery following storms. Data were gathered on winds, waves, flow velocities, and profile changes during three storm sequences. During the passage of low pressure centers, strong northwest winds (>8.0 m s-1) generated local waves with significant heights of 0.36 to 0.52 m and periodicities 3.6 to 4.9 s. Sediment was eroded from the upper foreshore and deposited as a thin veneer (<0.10 m) on the lower foreshore near mean low water. Profile recovery occurred during either locally generated estuarine or non-local ocean waves depending on tracks of pressure centers. Locally generated significant wave heights, ranging from 0.10 to 0.14 m with periodicities from 2.6 to 2.7 s, occurred during the retreating phase of a low pressure system passing to the south of the site or when pressure centers passed to the north and the site came under the influence of a retreating cold front. Significant heights of non-local ocean waves were 0.09 m with a periodicity of 9.1 s when low pressure centers advanced to the south of the site.

Rates of swash bar migration were similar under local estuarine and non-local ocean waves. Deposition on the upper foreshore during non-local ocean waves was less than measured during local waves due to lower wave heights and lower potential for longshore transport of sediment. Orientation of a beach to the mouth of the estuary seems to have more influence on the magnitude of ocean-wave energy reaching the shoreline than does proximity to the mouth. The greatest geomorphic contribution of non-local ocean waves to beach dynamics is after the passage of a weather system.