Storm Tide Amplification due to Estuary Urbanization and Harbor Development

In recent centuries, human activities have greatly modified the geomorphology of coastal regions, yet studies of historical and possible future changes in coastal flood extremes typically ignore the influence of geomorphic change. Here, we quantify the influence of 20^th Century manmade changes to Jamaica Bay, New York City, on present-day storm tides. Our work creates and validates a hydrodynamic model for the 1870s, based on detailed maps of bathymetry, seabed characteristics, topography, and tide observations, for use alongside a present-day model. Predominantly through dredging, landfill and inlet stabilization, the average water depth of the bay has changed from 1.7 to 4.5 m, tidal surface area from 92 to 72 km², and the inlet minimum cross-sectional area from 4800 to 8900 m². Total (freshwater plus salt) marsh habitat area has declined from 61 to 15 km² and intertidal unvegetated habitat area from 17 to 4.6 km². A probabilistic flood hazard assessment with simulations of 144 storm events reveals that the landscape changes caused an increase of 0.28 m (12%) in the 100-year storm tide, even larger than the influence of global sea level rise of 0.23 m since the 1870s. Specific anthropogenic changes to estuary depth, area and inlet depth and width are shown through targeted modeling and dynamics-based considerations to be the most important drivers of increasing storm tides. An initial comparison with several other urbanized U.S. East Coast estuaries reveals that increases to storm tides are common and have a spatial footprint in the estuary that depends on long-wave dynamics. We suggest that the ensemble storm simulation methodology described here should be applied to other estuaries to assess storm tide non-stationarity, since these storm tide changes depend both on storm features (track, speed, size) and on individual geomorphic features.