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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Flood risk management and adaptation : Hazard assessment from storm tides and rainfall on a tidal river estuary
Hazard assessment from storm tides and rainfall on a tidal river estuary
Author : P. ORTON(1), F. CONTICELLO(2), F. CIOFFI(3), T. HALL(4), N. GEORGAS(5), U. LALL(6) & A BLUMBERG(7)
ABSTRACT
Here, we report on methods and results for a model-based flood hazard assessment we have conducted for the Hudson
River from New York City to Troy/Albany at the head of tide. Our recent work showed that neglecting freshwater flows
leads to underestimation of peak water levels at up-river sites and neglecting stratification (typical with two-dimensional
modeling) leads to underestimation all along the Hudson. As a result, we use a three-dimensional hydrodynamic model
and merge streamflows and storm tides from tropical and extratropical cyclones (TCs, ETCs), as well as wet extratropical
cyclone (WETC) floods (e.g. freshets, rain-on-snow events). We validate the modeled flood levels and quantify error with
comparisons to 76 historical events.
A Bayesian statistical method is developed for tropical cyclone streamflows using historical data and consisting in the
evaluation of (1) the peak discharge and its pdf as a function of TC characteristics, and (2) the temporal trend of the
hydrograph as a function of temporal evolution of the cyclone track, its intensity and the response characteristics of the
specific basin. A k-nearest-neighbors method is employed to determine the hydrograph shape. Out of sample validation
tests demonstrate the effectiveness of the method. Thus, the combined effects of storm surge and runoff produced by
tropical cyclones hitting the New York area can be included in flood hazard assessment.
Results for the upper Hudson (Albany) suggest a dominance of WETCs, for the lower Hudson (at New York Harbor) a
case where ETCs are dominant for shorter return periods and TCs are more important for longer return periods (over 150
years), and for the middle-Hudson (Poughkeepsie) a mix of all three flood events types is important. However, a possible
low-bias for TC flood levels is inferred from a lower importance in the assessment results, versus historical event top-20
lists, and this will be further evaluated as these preliminary methods and results are finalized. Future funded work will
quantify the influences of sea level rise and flood adaptation plans (e.g. surge barriers). It would also be valuable to
examine how streamflows from tropical cyclones and wet cool-season storms will change, as this factor will dominate at
upriver locations.
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Flood risk management and adaptation
Date Published : 18/08/2015
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