Abstract
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 man-made changes to Jamaica Bay, New York City, on present-day 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 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 about 0.23 m since the 1870s. Specific anthropogenic changes to estuary depth and area as well as inlet depth and width are shown through targeted modeling and dynamics-based considerations to be the most important drivers of increasing storm tides.
Highlights
The characteristics of storm tides and the probability of flooding depend on both far-field forcing and on local characteristics
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
The most dramatic land cover change is from large areas of fringing wetlands to urbanized areas, and the center of the bay has shifted from marshes to open waters
Summary
The characteristics of storm tides and the probability of flooding depend on both far-field forcing (meteorological, tidal) and on local characteristics (bathymetry, bottom roughness, floodplain size). Long-term cycles in astronomic forcing (e.g., the 18.6-year nodal cycle) affect both nuisance flooding (Ray and Foster, 2016) and the probability of high-impact events (Talke et al, 2018). A recent study of New York Harbor (NYH) showed an increase in the 10-year storm tide of 0.28 m since the mid-1800s in addition to the local relative sea level rise of 0.44 m (Talke et al, 2014)
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