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.

Plain Language Summary

High tide floods (HTFs) are shallow coastal flooding events that typically occur near the time of predicted high tide. Here we isolate and examine how sea‐level rise (SLR) and historical landscape changes related to urban development have altered tides and increased flooding frequency in Jamaica Bay, New York City. Using water level observations and digitized maps from the 1870s, we create a computer‐based model to study how HTF frequency has changed from the 1870s to now. Model results indicate that dredging and wetland landfill increased tidal ranges in the bay by nearly 20%. We then use a model simulation of 2020 to evaluate the effects of both SLR and the changed landscape on the annual number of HTF events. Results show that of 15 minor flood events in 2020, only one would have occurred without SLR and two would have occurred without landscape changes since the 1870s. A better understanding of how specific landscape changes have affected tides and caused increases in coastal flooding can help mitigation efforts and provide more rationale for restoration and nature‐based solutions.

Key Points

• Landscape change since the 1870s (e.g., dredging, land filling) increased tidal range by 20% in Jamaica Bay, New York City

• These landscape changes reduced inlet choking and increased tidal reflection, resulting in a frequency‐dependent amplification of tides

• Of 15 minor floods in 2020, there would have been only two without landscape change and one without sea level rise since the 1870s