Storm tide amplification and habitat changes due to urbanization of a lagoonal estuary

Abstract

In recent centuries, human activities have greatly modified the geomorphology of coastal regions. However, studies of historical and possible future changes in coastal flood extremes typically ignore the influence of geomorphic change. Here, we quantify the influence of 20th-century manmade changes to Jamaica Bay, New York City, on presentday storm tides. We develop and validate 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 increased from 1.7 to 4.5 m, tidal surface area decreased from 92 to 72 km2, and the inlet minimum cross-sectional area expanded from 4800 to 8900m2. 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 0.28m (12 %) in the 100-year storm tide, even larger than the influence of global sea level rise of about 0.23m since the 1870s. Specific anthropogenic changes to estuary depth and area as well as inlet depth and width are shown through targeted modeling and dynamicsbased considerations to be the most important drivers of increasing storm tides.