Skew surge and extreme coastal flooding events in the Delaware and Chesapeake Bays of the US Mid-Atlantic coast for 1980-2019
Date
2021
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Publisher
University of Delaware
Abstract
Coastal storms are a multi-threat hazard to the Mid-Atlantic region of the US East Coast. They bring heavy precipitation, strong winds, large waves, extensive flooding, and dangerous rip currents. Of all these threats, it is coastal flooding that poses the greatest risk to human life and is often the source of much of the damage. The Mid-Atlantic is a heavily populated and commercially active region with many of its natural resources and man-made infrastructure located along its coasts. However, this region is directly impacted by tropical cyclones (TCs) and extra-tropical cyclones (ETCs), and is also a hotspot of sea-level rise (SLR), with relative rates of SLR approximately twice that of the global mean sea level. Extreme coastal flooding events are commonly associated with multiple simultaneous threats and can overwhelm many protections in place. Albeit rare, the net negative effect due to an extreme coastal storm is profound and often is greater than the sum of its parts. SLR, frequency of minor and major flooding, and the frequency and intensity of major TCs, are all expected to increase in the region under current future global warming scenarios. ☐ The three studies described in this dissertation investigate tropical cyclone and mid-latitude weather system-caused extreme storm surge events in the Mid-Atlantic by analyzing tide gauge data throughout the Delaware and Chesapeake Bays over the time period 1980 – 2019. Focus is on storm events that produced the largest meteorological component of coastal flood levels, approximated by the skew surge metric. Skew surge, defined as the difference between the maximum observed total water level and the maximum predicted tide during a tidal cycle, even if the observed and predicted tidal peaks are offset (i.e., skewed) from each other, is arguably the most appropriate measure for long-term planning and estimating extreme storm surges. ☐ Extreme surge events from mid-latitude weather systems have strong seasonal dependence (primarily during Oct – Apr) and occur much more often than from tropical cyclones (almost exclusively occurring during Sep – Oct). Within the Delaware Bay and upper Chesapeake Bay, TCs account for 30-45% of the 10 largest surge events whereas the lower Chesapeake Bay has a higher percentage of TCs at 40 – 45%. Across all regions, the percent of TCs approaches 10-15% for larger numbers of top events. Location of TC storm track play a significant role on extreme surge levels, however, the relationship nearly disappears at lower levels. TCs that stayed offshore to the east of Delmarva result in larger surges in the lower bays, whereas tracks that stayed to the west commonly result in larger surges in the upper bays. Similarly, the atmospheric circulation patterns with respect to sea-level pressure and 500 mb geopotential height fields play a large role in extreme surges produced by mid-latitude weather systems. Low-pressure centers to the south and west of Delmarva, and high-pressure centers to the north and east, are aligned under an area of upper-level divergence to the east of a geopotential height trough. Lastly, throughout the study area, 100-year return levels are largest at Lewes, DE, and Sewells Pt, MD, each located in the lower southwest portion of their respective bays. ☐ Overall, the primary goals of this work are to enhance scientific understanding, to promote public awareness, and to aid in long-term planning of extreme coastal flooding events in the Mid-Atlantic region.
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Keywords
Coastal flooding, Coastal processes, Natural hazards, Storm surge, Tidal analysis, Tropical cyclones