The Overtide and Filtering Response of Small Inlet/Bay Systems

  • Joseph L. DiLorenzo
Part of the Lecture Notes on Coastal and Estuarine Studies book series (COASTAL, volume 29)


When the tide propagates from the deep ocean towards shallower coastal regions, its spectral composition changes as energy from the dominant offshore tidal constituents is transferred to higher harmonic components of the tide called “overrides”. The relative magnitude of the overrides generated in a coastal waterway by shoaling processes depends primarily upon the local geomorphology and the ocean tidal forcing. In this study, a simple analytical model is developed to investigate the override and filtering response of a special class of small inlet/bay systems to ocean sea level forcing. This model relates the fundamental and first overtide components of the pumping mode response of inlet/bay systems to the relevant governing parameters. The tendency towards flood/ebb dominance also is related to the governing parameters in a simple but general manner. It is demonstrated to first order that an inlet/bay system responds to ocean sea level forcing as a filter whose characteristics are controlled largely by system geometry and by ocean forcing characteristics. The modeled frequency response for the first overtide component in this special class of tidal inlet systems is shown to be similar to the parent, fundamental component response discussed by Özsoy (1978). However, there are greater amplifications for the overtide component responses, and lower cutoff frequencies. The resulting harmonic distortions in inlet currents are determined from the model solutions for the M2 and M4 phase lags. Systems having short Helmholtz periods exhibit the same tidal distortions found at the ocean entrance, while systems having progressively greater natural periods diverge from the ocean entrance distortions in a manner described by model solutions. Analytical solutions for the fundamental and first overtide components are compared to numerical solutions for verification purposes. Implications regarding the tidally-induced import or export of coarse sediment in these systems are discussed. The utility of the model is demonstrated for the Peconic Bay system. The analytical model describes the principal features of the Peconic Bay response, and suggests a possible stability mechanism for the system. The analytical model also is utilized to provide a simple physical explanation for the association of flood dominance with time variations in cross-sectional area, and ebb dominance with time variations in surface area.


Tidal Inlet Frictional Dissipation Inlet Cross Section Fresh Water Inflow Tidal Distortion 
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Copyright information

© Springer Science+Business Media New York 1988

Authors and Affiliations

  • Joseph L. DiLorenzo
    • 1
  1. 1.One Industrial Way WestNajarian & Associates, Inc.EatontownUSA

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