Talke Stefan

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Talke
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Stefan
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  • Article
    Bigger tides, less flooding: Effects of dredging on barotropic dynamics in a highly modified estuary.
    (American Geophysical Union, 2018-12-11) Ralston, David K. ; Talke, Stefan ; Geyer, W. Rockwell ; Al‐Zubaidi, Hussein A. M. ; Sommerfield, Christopher K.
    Since the late nineteenth century, channel depths have more than doubled in parts of New York Harbor and the tidal Hudson River, wetlands have been reclaimed and navigational channels widened, and river flow has been regulated. To quantify the effects of these modifications, observations and numerical simulations using historical and modern bathymetry are used to analyze changes in the barotropic dynamics. Model results and water level records for Albany (1868 to present) and New York Harbor (1844 to present) recovered from archives show that the tidal amplitude has more than doubled near the head of tides, whereas increases in the lower estuary have been slight (<10%). Channel deepening has reduced the effective drag in the upper tidal river, shifting the system from hyposynchronous (tide decaying landward) to hypersynchronous (tide amplifying). Similarly, modeling shows that coastal storm effects propagate farther landward, with a 20% increase in amplitude for a major event. In contrast, the decrease in friction with channel deepening has lowered the tidally averaged water level during discharge events, more than compensating for increased surge amplitude. Combined with river regulation that reduced peak discharges, the overall risk of extreme water levels in the upper tidal river decreased after channel construction, reducing the water level for the 10‐year recurrence interval event by almost 3 m. Mean water level decreased sharply with channel modifications around 1930, and subsequent decadal variability has depended both on river discharge and sea level rise. Channel construction has only slightly altered tidal and storm surge amplitudes in the lower estuary.
  • Article
    Mechanics and historical evolution of sea level blowouts in New York harbor
    (MDPI, 2019-05-23) Gurumurthy, Praneeth ; Orton, Philip M. ; Talke, Stefan ; Georgas, Nickitas ; Booth, James F.
    Wind-induced sea level blowouts, measured as negative storm surge or extreme low water (ELW), produce public safety hazards and impose economic costs (e.g., to shipping). In this paper, we use a regional hydrodynamic numerical model to test the effect of historical environmental change and the time scale, direction, and magnitude of wind forcing on negative and positive surge events in the New York Harbor (NYH). Environmental sensitivity experiments show that dredging of shipping channels is an important factor affecting blowouts while changing ice cover and removal of other roughness elements are unimportant in NYH. Continuously measured water level records since 1860 show a trend towards smaller negative surge magnitudes (measured minus predicted water level) but do not show a significant change to ELW magnitudes after removing the sea-level trend. Model results suggest that the smaller negative surges occur in the deeper, dredged modern system due to a reduced tide-surge interaction, primarily through a reduced phase shift in the predicted tide. The sensitivity of surge to wind direction changes spatially with remote wind effects dominating local wind effects near NYH. Convergent coastlines that amplify positive surges also amplify negative surges, a process we term inverse coastal funneling.