Water level response to 1999 Hurricane Floyd in the Chesapeake Bay

During the passage of Hurricane Floyd, a unique water level fluctuation occurred in the Chesapeake Bay with double high peaks of storm tide in the lower Bay and a moderate set-down in the upper Bay. The response of water level inside the Bay to the hurricane has been studied through analysis of observations and model simulations. The ADvance CIRculation (ADCIRC) model was applied to the Chesapeake Bay for this study. A high-resolution tide and storm surge model capable of storm surge prediction has been developed for the Bay. The study shows that the water level variation during the hurricane inside the Bay can be well explained by the superposition of two distinct physically driven mechanisms: storm tide that developed in the offshore regions propagating into the Bay and surge generated by local wind. The double peaks of storm tide that occurred in the lower Bay regions are mainly caused by the tidal component, which modulates the incoming surge wave generated in the offshore regions. The model experiments show that the incoming storm tide can propagate to the head of the estuary without much attenuation. Consequently, the superposition of the surge generated by the local northeasterly and northwesterly winds and the incoming storm tide results in an enhanced set-up in the lower Bay region, while the set-down in the upper Bay regions is reduced. The offshore water level variation influences the lower Bay regions more significantly. The storm tide propagating into the Bay accounts for most of the water level variation in the lower Bay regions during the storm.