**1. Introduction**

The influence of sea level rise (SLR) on coastal storm responses is highly complex and not well understood. It has been shown that the impact of SLR on storm tide and surge can vary greatly over small spatial scales [1, 2] though the causes of these variations, likely regionally specific, have not been thoroughly explored. Due to the limited understanding of small-scale uncertainties, linear relationships between SLR and storm response patterns are commonly assumed when modeling SLR scenarios for risk management. This study is aimed at investigating the variability of storm responses sensitive to SLR along the coastline of Saco Bay and Casco Bay in the Gulf of Maine through the application of a hydrodynamic coastal ocean model. The coastline across these two bays varies greatly in topography and intertidal characteristics, which has been shown to be a major factor affecting the impact of SLR on storm surge [3]. Furthermore, coastal flooding caused by northeasters

along the New England coastline is a common occurrence during the cool seasons when cyclogenesis is driven by dynamic atmospheric forcing associated with the jet stream. This makes accurate predictions of storm response of great importance to the coastal communities.

During the October–April period, the extratropical storms affecting this domain are characterized by large, synoptic-scale cyclones, heavy precipitation, and strong wind and are accompanied by wave run-up and sea level setup. As a result, northeasters in this region often result in significant damages including loss of life and property, as well as environmental impacts such as beach erosion. The latter is particularly notable in Saco Bay in northern New England, where beach erosion has been a major issue for several decades. Conversely, in the same area, tropical cyclones are often smaller and move faster, resulting in less time for storm surges to develop over these shallow areas [4], and typically transition into extratropical cyclones before landfall. As such, this study will primarily focus on major extratropical storm events. Scarcity of real-time observation data during these storms has led to an increased reliance on numerical model results for storm forecasts along the coastline [4]. Testing the developed hydrodynamic model against these extreme events across varying SLR scenarios will also help ensure the model's capability in modeling future events.

This study was designed to quantify the relationship between sea level rise and coastal storm responses in Saco Bay and Casco Bay. In doing so, improved forecasts can be provided to coastal communities in preparation for future storm events. To accomplish these goals, a predictive storm response model was developed, building upon the Finite-Volume Coastal Ocean Model (FVCOM) [5]. Inputs for this model were derived from the Northeast Coastal Ocean Forecast System (NECOFS, http://www.smast.umassd.edu:8080/thredds/catalog/models/ fvcom/NECOFS/Archive/catalog.html) and the United States Geological Survey (USGS, https://waterdata.usgs.gov/nwis). Validation of the resultant model was carried out with data collected from NOAA buoys and stations, the University of Maine buoy deployments, and the Sustainable Ecological Aquaculture Network (SEANET). Buoy records and tidal station data along with the validated model simulation were used to establish a baseline assessment of the bays. Storm simulations were then analyzed to identify and dissect storm responses to be tracked across a range of sea level rise scenarios.

The present investigation differentiates itself from past studies in three prominent ways. First, no hydrodynamic model study has been conducted over this domain at the high-resolution used herein. By simulating storms with the minimum 10-m resolution nearshore, we can identify very-small-scale features and provide more accurate dynamic inundation and storm response predictions than what is currently available. Additionally, the methodology of tracking modeled storm responses under elevating SLR scenarios has not yet been applied to the Gulf of Maine, a region particularly vulnerable to the impacts of northeasters. Finally, this study provides a comparison of storm responses and SLR vulnerability in two adjacent bays, distinct from each other in geomorphological and hydrodynamic characteristics.

The following section provides a review of studies contributing to the understanding of SLR storm response interactions and includes a brief overview of the Saco and Casco domain and of the storm events being examined. The rest of the paper is organized as follows. The design, configuration, and validation of the model are discussed in Section 3, followed by an analysis in Section 4 to depict the modeled storm responses. Section 5 looks at the modeled responses in the events of sea level rise, including inundation and circulation patterns. Finally, Section 6 provides a summary of the findings revealed by this study.

*Linear and Nonlinear Responses to Northeasters Coupled with Sea Level Rise: A Tale of Two Bays DOI: http://dx.doi.org/10.5772/intechopen.87780*
