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Woods Hole Coastal and Marine Science Center

Woods Hole Coastal and Marine Science Center > Coastal Model Applications and Field Measurements > Research Activities > Hudson Shelf Valley Dynamics

Coastal Model Applications and Field Measurements

Currents and sediment transport in the Hudson Shelf Valley

USGS made sediment transport observations in the Hudson Shelf Valley (HSV) in winter 1999-2000, and in the spring of 2006.  These measurements have been combined with others to provide a description of the monthly mean flow in the HSV and to investigate the dynamics of the up-valley and down-valley flow.  Based on these observations and measured water levels, calculations indicate that down-valley flow during Hurricane Sandy could have reached 1.5 m/s.  This may have moved fine-grain sediment and associated contaminants from the area of sediment and contaminant accumulation at the valley head.  Model assessments should provide further insight into the effects of Sandy on this system.

Hudson Shelf Valley is a 20-30 m deep, 5-10 km wide v-shaped submarine valley that extends across the Middle Atlantic Bight continental shelf. The valley provides a conduit for cross-shelf exchange via along-valley currents of 0.5 m s-1 or more. Current profile, pressure, and density observations collected during the winter of 1999-2000 are used to examine the vertical structure and dynamics of the flow. Near-bottom along-valley currents having times scales of a few days are driven by cross-shelf pressure gradients set up by wind stresses, with eastward (westward) winds driving onshore (offshore) flow within the valley. The along-valley momentum balance in the bottom boundary layer is predominantly between the pressure gradient and bottom stress because the valley bathymetry limits current veering. Above the bottom boundary layer the flow veers toward an along-shelf (cross-valley) orientation and a geostrophic balance with some contribution from the wind stress (surface Ekman layer). The vertical structure and strength of the along-valley current depends on the magnitude and direction of the wind stress. During offshore flows driven by westward winds the near-bottom stratification within the valley increases resulting in a thinner bottom boundary layer and weaker offshore currents. Conversely, during onshore flows driven by eastward winds the near-bottom stratification decreases resulting in a thicker bottom boundary layer and stronger onshore currents.  Consequently onshore along-valley transport associated with eastward wind stress exceeds the offshore transport associated with westward wind stress of the same magnitude. 

Monthly-averaged along-axis flow in the Hudson Shelf Valley

Monthly-averaged near-bottom along-axis flow in the Hudson Shelf Valley is up-canyon throughout the year (up-canyon is negative in plot). Up-canyon flow is ~ 0.1 m/s in winter and less than 0.05 m/s in summer (from Lentz and others, 2014).

 

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