Chant Robert J.

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Chant
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Robert J.
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Wave generation, dissipation, and disequilibrium in an embayment with complex bathymetry

2018-10-04 , Chen, Jia-Lin , Ralston, David K. , Geyer, W. Rockwell , Sommerfield, Christopher K. , Chant, Robert J.

Heterogeneous, sharply varying bathymetry is common in estuaries and embayments, and complex interactions between the bathymetry and wave processes fundamentally alter the distribution of wave energy. The mechanisms that control the generation and dissipation of wind waves in an embayment with heterogeneous, sharply varying bathymetry are evaluated with an observational and numerical study of the Delaware Estuary. Waves in the lower bay depend on both local wind forcing and remote wave forcing from offshore, but elsewhere in the estuary waves are controlled by the local winds and the response of the wavefield to bathymetric variability. Differences in the wavefield with wind direction highlight the impacts of heterogeneous bathymetry and limited fetch. Under the typical winter northwest wind conditions waves are fetch‐limited in the middle estuary and reach equilibrium with local water depth only in the lower bay. During southerly wind conditions typical of storms, wave energy is near equilibrium in the lower bay, and midestuary waves are attenuated by the combination of whitecapping and bottom friction, particularly over the steep, longitudinal shoals. Although the energy dissipation due to bottom friction is generally small relative to whitecapping, it becomes significant where the waves shoal abruptly due to steep bottom topography. In contrast, directional spreading keeps wave heights in the main channel significantly less than local equilibrium. The wave disequilibrium in the deep navigational channel explains why the marked increase in depth by dredging of the modern channel has had little impact on wave conditions.

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Effects of locally generated wind waves on the momentum budget and subtidal exchange in a coastal plain estuary

2019-01-28 , Pareja‐Roman, L. Fernando , Chant, Robert J. , Ralston, David K.

A numerical model with a vortex force formalism is used to study the role of wind waves in the momentum budget and subtidal exchange of a shallow coastal plain estuary, Delaware Bay. Wave height and age in the bay have a spatial distribution that is controlled by bathymetry and fetch, with implications for the surface drag coefficient in young, underdeveloped seas. Inclusion of waves in the model leads to increases in the surface drag coefficient by up to 30% with respect to parameterizations in which surface drag is only a function of wind speed, in agreement with recent observations of air‐sea fluxes in estuaries. The model was modified to prevent whitecapping wave dissipation from generating breaking forces since that contribution is integrally equivalent to the wind stress. The proposed adjustment is consistent with previous studies of wave‐induced nearshore currents and with additional parameterizations for breaking forces in the model. The mean momentum balance during a simulated wind event was mainly between the pressure gradient force and surface stress, with negligible contributions by vortex, wave breaking (i.e., depth‐induced), and Stokes‐Coriolis forces. Modeled scenarios with realistic Delaware bathymetry suggest that the subtidal bay‐ocean exchange at storm time scales is sensitive to wave‐induced surface drag coefficient, wind direction, and mass transport due to the Stokes drift. Results herein are applicable to shallow coastal systems where the typical wave field is young (i.e., wind seas) and modulated by bathymetry.

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Data and numerical methods for determining the dynamics and kinematics of Newark Bay, NJ

2019-07-30 , Corlett, W. Bryce , Geyer, W. Rockwell , Chant, Robert J. , Ralston, David K. , Sommerfield, Christopher K.

These observational data and numerical methods were used to investigate the subtidal salt balance of Newark Bay, a sub-estuarine network connected to the Hudson River estuary through New York Harbor. The moored data were collected in 2008 by Chant and Sommerfield, and in 2016 by Corlett, Geyer, and Ralston. Corlett devised the included numerical methods. Shipboard measurements of the vertical salinity profile near each mooring were used to reconstruct the tidally-varying vertical salinity profile from near-bed and near-surface salinity measurements at each mooring. The effects of tidal processes, such as frontal advection, on the exchange flow were investigated by applying the isohaline total exchange flow (TEF) framework to the mooring-based observations in multiple reaches of the estuarine network. In addition, a TEF-based salt balance was derived for the purpose of directly comparing the TEF framework with the standard Eulerian framework.

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