Linear and Nonlinear Responses to Northeasters Coupled with Sea Level Rise: A Tale of Two Bays

Abstract

This study aimed at dissecting the influence of sea level rise (SLR) on storm responses in two bays in the Gulf of Maine through high-resolution, three-dimen-sional, hydrodynamic modeling. Saco Bay, an open bay characterized by gentle coastal slopes, provided a contrast to Casco Bay that has steep shorelines and is shel-tered by barrier islands and peninsulas. The Finite-Volume Coastal Ocean Model (FVCOM) was implemented for Saco Bay and Casco Bay to simulate the February 1978 northeaster and an April freshwater discharge event in 2007 following the Patriots Day storm. Both events were repeatedly simulated under SLR scenarios ranging from 0 to 7 ft. Modeled storm responses were identified from the 1978 Blizzard simulations and were tracked across SLR scenarios. By comparing changes in inundation, storm currents, and salinity distribution between the two bays, freshwater discharge and bathymetric structure were isolated as two determining factors in how storm responses change with the rising sea level. The steplike bottom relief at the shoreline of Casco Bay sets up nonlinear responses to SLR. In contrast, storm responses in Saco Bay varied significantly with SLR due to alterations in river dynamics attributed to SLR-induced flooding.