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IMPACTS OF RELATIVE SEA LEVEL RISE ON COASTAL FLOODING RECURRENCE INTERVALS IN THE NORTHEASTERN USA
Sea level elevation relative to land (RSL) is related to both ASL rise and geologic processes that affect a specific region, including tectonic uplift and down dropping, isostatic rebound and depression, land surface changes due to compaction, dewatering, fluid extraction, and diagenetic processes.
Sea level data from the NOAA/NOS Tides and Current web site were obtained for five sites: Boston, Woods Hole, New London, New York City, and Atlantic City, The first step in data reduction involved removing trends in sea level rise from the raw time series. The linear regression slopes provided by NOAA/NOS were used to remove the historical trends in sea level rise at each station. Theoretical tidal variations from the NOAA/NOS tide model for each station were then subtracted from the detrended sea level time series. The resulting datasets were defined as sea level anomalies. We selected a threshold of 25 cm to remove positive anomalies that could be attributed to model error. Cluster analysis was performed on the anomaly time series to remove multiple anomalies from the same storm. We selected the maximum of these within-storm anomalies to represent the storm surge height
The last step in this process was to add in the tidal component so that storm surge heights could be converted to water level elevations. To be conservative, we used mean higher high water (MHHW) to represent tide height. The difference between MHHW and mean sea level, relative to the North American Vertical Datum of 1988 was used to represent the tidal height and was added to the storm surge heights computed for each station. Wave runup elevation impacts were not included; they can be significant right along the coastline. The result of these analyses show that what we consider extreme events now could become much more commonplace in the future.