Physical Dynamics in the Hudson River Estuary

Katherine Nickerson

Katherine Nickerson

The Hudson River Estuary

http://education.nationalgeographic.com/media/photos/000/283/28314.jpg

• Unusual hybrid of estuarine types

• Elements of fjord, salt-wedge and coastal plain estuaries

• Highly interactive with Hudson River

• Tides, Salinity, Density

• Partially mixed estuary

• Tide-induced mixing

• Salinity varies with season, spring/neap tides, and freshwater discharge

• Estuarine "salt wedge"

Estuarine Circulation

• Strong horizontal salinity and density gradients

• Creates a baroclinic pressure gradient

• Deep water driven landward by pressure gradient

• Surface water moves seaward due to surface slope

• Moves salt into estuary against river flow

• Stronger circulation with stronger gradients

• More vigorous circulation at high river flow

http://www.chesapeakequarterly.net/images/uploads/siteimages/CQ/V12N3/Estuarine-circulation_pritchard-large.png

Stratification• Partially Mixed estuary

• Closely related to amount of vertical mixing

• Dependent on difference between salinity in top and bottom layers

• Transport increases proportional to difference

• Drives physical exchange processes

• Biogeochemistry, ecology

• Most important factor in estuary classification

• Estuarine circulation strengthens stratification

http://www.ozcoasts.gov.au/indicators/images/salinity_structure.jpg

Tidal Influences• Major energy source in the estuary

• Mixes vertically, affects stratification• Affects estuarine circulation, which provides

the source of stratification

• Large spring-neap differences

• Generates turbulence

• Stronger stratification increases shear instability, suppresses turbulence

• Both cause mixing

• Tidal excursion: Distance a parcel of water is transported by tide in half a cycle

http://inhabitat.com/stacy-levys-tide-flowers-bloom-with-the-rising-waters-of-the-hudson-river/

New York Harbor Complex

• Flow is driven primarily by tidal straits• Sea level changes driven by tidal and

meteorological forcing• Two-layer flow is persistent, but not as

important• East River

• Tidal strait, not river• Connects to Long Island Sound• Among the strongest flows

• Kill Van Kull• Connects to Newark Bay• Effective at mixing water; tidal excursion

longer than strait• Arthur Kill

• Connects Raritan Bay to Newark Bay• Ineffective at mixing water; tidal

excursion shorter than strait• Raritan River and Passaic River major

freshwater inputs Geyer and Chant, 2006

Works Cited

WR Geyer, R Chant. The Physical Oceanography Processes in the Hudson River Estuary. The Hudson River Estuary, 13-23

W. Rockwell Geyer, John H. Trowbridge, and Melissa M. Bowen, 2000: The Dynamics of a Partially Mixed Estuary*. J. Phys. Oceanogr., 30, 2035–2048.