Local land subsidence in Miami Beach (FL) and Norfolk (VA) and its contribution to flooding hazard in coastal communities along the U.S. Atlantic coast

Abstract

Increasing rate of sea level rise (SLR) along the US Atlantic coast has resulted in increasing flooding hazard in several coastal communities, including Boston (MA), Norfolk (VA), and Miami Beach (FL). Here, we evaluate the contribution of local land subsidence to coastal flooding hazard in two communities, Miami Beach and Norfolk, using Interferometric Synthetic Aperture Radar (InSAR) time series observations. The InSAR analysis relies on two data sets of ERS-1/2 scenes that were acquired during 1992–1999. The long period covered by the data sets and the large number of available scenes (>20), allowed us to detect movements with lower uncertainty levels (up to 2.4 mm/yr) compared to previous studies. Our results revealed the occurrence of localized subsidence in both communities. In Miami Beach, subsidence at rates of 1–3 mm/yr occurred in a small portion of the territory, mainly in parts of the city built on reclaimed wetlands. In Norfolk, relative subsidence occurred in several localized areas, some along the shore and some inland, at rates of 1–3 mm/yr, while only few sectors show subsidence up to 6 mm/yr. In these areas, the subsidence is higher and reaches ~8 mm/yr if the combined effects of regional-scale (~1.7 mm/yr) and InSAR-derived subsidence is considered. The subsidence observed in this study indicates localized areas of relative higher rate of SLR and a potential increased coastal flooding hazard for both communities.