Impact of sea level rise on tidal range in Chesapeake and Delaware Bays

Coastal inundation is affected not only by rising mean sea level but also by changing tides. A numerical model is developed to investigate how sea level rise and coastline changes may impact tides in two coastal-plain estuaries, Chesapeake Bay and Delaware Bay. Despite their different tidal characteristics, the two estuaries display similar responses to the sea level rise and shoreline management scenarios. When hypothetic sea walls are erected at the present coastline to prevent low-lying land from flooding, tidal range increases, with greater amplification in the upper part of the two estuaries. When low-lying land is allowed to become permanently inundated by higher sea level, however, tidal range in both estuaries decreases. Analyses of the tidal energy budget show that the increased dissipation over the shallow water and newly inundated areas compensates for the reduced dissipation in deep water, leading to smaller tidal range. The changes in the tidal range are not proportional to the changes in the mean sea level, indicating a nonlinear tidal response to sea level rise. The ratio of tidal range change to sea level rise varies between -0.05 and 0.1 in Chesapeake Bay and between -0.2 and 0.25 in Delaware Bay. The model results suggest a potential adaptation strategy that uses inundation over low-lying areas to reduce tidal range at up-estuary locations. Plain Language Summary Coastal inundation occurs when sea levels are higher than the normal extent of the tide. Presently, estimates of future coastal inundation due to sea level rise are made by simply adding the expected sea level rise to the present-day tides. However, tides are themselves affected by changes in water depth, thus sea level rise will change the position of high and low tide. In this study, we investigate how sea level rise will change tides in two large coastal waterways, Chesapeake and Delaware Bays. We also investigate how tides will be affected if shoreline protection measures are put in place to prevent rising sea levels from encroaching over low-lying land. We find that if no shoreline protection measures are installed, higher sea levels will reduce tides in both Chesapeake and Delaware Bays. Adding shoreline protection measures however increases the tides, particularly in the upper reaches of both estuaries, where major cities are located.