Effect of Estuary Urbanization on Tidal Dynamics and High Tide Flooding in a Coastal Lagoon

Abstract

High tide floods (HTFs) are minor, shallow flooding events whose frequency has increased due to relative sea-level rise (SLR) and secular changes in tides. Here we isolate and examine the role of historical landscape change (geomorphology, land cover) and SLR on tides and HTF frequency in an urbanized lagoonal estuary: Jamaica Bay, New York. The approach involves data archeology, historical (1870s) map digitization, as well as numerical modeling of the bay. Numerical simulations indicate that a century of landscape alterations (e.g., inlet deepening and widening, channel deepening, and wetland reclamation) increased the mean tidal range at the head of the bay by about 20%. The observed historical shift from the attenuation to amplification of semidiurnal tides is primarily associated with reduced tidal damping at the inlet and increased tidal reflection. The 18% decrease in surface area exerts a minor influence. A 1-year (2020) water level simulation is used to evaluate the effects of both SLR and altered morphology on the annual number of HTFs. Results show that of 15 “minor flood” events in 2020, only one would have occurred without SLR and two without landscape changes since the 1870s. Spectral and transfer function analyses of water level reveal frequency-dependent fingerprints of landscape change, with a significant decrease in damping for high-frequency surges and tides (6–18 hr time scale). By contrast, SLR produced only minor effects on frequency-dependent amplification. Nonetheless, the geomorphic influence on the dynamical response significantly increases the vulnerability of the system to SLR, particularly high-tide flooding.