Storm Induced Water Levels In Norfolk Virginia And Chesapeake Bay: A Model And Observations

Bao S, Leonard J. Pietrafesa, Yan T, Peng M and Gayes PT

An assessment of storm induced water levels in Norfolk Virginia (VA) and Chesapeake Bay using an interactively coupled wave and current numerical model driven by a numerical atmospheric model versus actual observations is presented. The reason for the interactive coupling is that this type of model coupling has been found to greatly improve coastal inundation modeling in another coastal domain. The model system is applied in an area where coastal flooding is likely to increase in the near future and beyond, because the Norfolk VA area has been found to be a “hot spot” along the eastern seaboard as regards rising coastal water levels along the U.S. Atlantic Eastern Seaboard. To assess the variability of sea level we conducted an empirical decomposition of the Sewell’s Point water level data and found that there are eight modes of variability ranging from monthly to seasonal to annual to inter-annual to 5-7 years to 10-12 years to about 25 years, with an overall upward trend which has varied from 0.35 t0 0.85 cm/year and is presently 0.65 cm/year. As modes 1 through 7 all have separate temporal periods of oscillation it is unlikely for all seven modes to be positive or negative at any particular time, however that occurrence is a possibility, and if that were to occur, the base water level could be 20 or 35 cm or 50 cm higher. Our numerical model results are validated against National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) observed wind fields, and National Ocean Service (NOS) water levels and surface gravity wave significant wave field heights, collected in the Chesapeake Bay domain, show excellent agreement. Given our documented assessment of the variability of coastal water level along the southern VA coastline, future, hurricanes and winter cyclones will subject the Norfolk region to far more coastal inundation and flooding in excess and more frequently than what it has experienced in the past. Norfolk residents will very likely experience frequent “nuisance” flooding and coastal erosion during periods of even moderately strong atmospheric winds associated with the passages of typical winter storms, especially Mid-Latitude cyclones and tropical cyclones; especially during high tides.