6/30/08 CMOP Seminar: The Response of a Partially-Stratified Estuary to Changes in River Flow and Tidal Amplitude
Jim Lerczak, Ph.D. from OSU to present on June 30th
TITLE
The Response of a Partially-Stratified Estuary to Changes in River Flow and Tidal Amplitude
SPEAKER
Jim Lerczak, Ph.D.
WHERE
OHSU West Campus, Paul Clayton Building, Room PC401
ABSTRACT
The Hudson River estuary is a partially-stratified estuary adjacent to New York City for which vertical stratification of salinity and the strength of its estuarine exchange circulation are both strongly dependent on the strength of river flow and on the amplitude of tidal currents. The length of the estuary – i.e., the landward extend of the salinity intrusion – also varies significantly. During high flow conditions in the spring, the estuary can undergo factor-of-three oscillations in length (from <30 km to >100 km in length) with fortnightly variations in tidal amplitude. Late in the summer, when river flow is comparatively weak, variations in length are muted, and the estuary approaches a steady length.
Using data collected over the last 15 years and a linear response model based on the global estuarine salt balance, we quantify the amplitude of variations in the length of the Hudson estuary and the time-scale over which the estuary responds to variations in river flow and tidal amplitude. This analysis shows that the response time scale of the estuary can vary by more than an order of magnitude, depending on the strength of river flow. When river flow is strong, the response time scale is ~2-3 days allowing the estuary to effectively respond to changes in the tides. When river flow is comparatively weak, the response time is long (~30 days) compared to the fortnightly cycle. The estuary cannot keep pace with tidal variations and the estuary approaches a steady length.
SPEAKER BIO
Jim Lerczak is a physical oceanographer at Oregon State University. His research interests are in coastal physical oceanography including the study of internal tides, high-frequency internal waves, and circulation in the vicinity of fronts; estuarine oceanography including the dynamics that drive the three-dimensional circulation, the mechanisms that transport and disperse materials within estuaries, and the time response of estuaries to changes in forcing; physical/biological interactions which influence larval dispersal.
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