**3.2 Model validation**

In situ observations from multiple sources were used to validate the model. Data from the NOAA-operated tidal stations (http://tidesand currents.noaa.gov/) were used for the sea surface height and water temperature validation. The University of Maine Physical Oceanography Group initiated the development of the Gulf of Maine Ocean Observing System (GoMOOS) in 2001 [24]. The moored buoys designed for this project were equipped with sensors specific to their installation site in addition to a standard set of instruments allowing for the collection and archive of wind speed and direction, visibility, air temperature, wave parameters, water temperature, and conductivity at 1-m depths and current velocity at 2-m depths [25]. For the Saco and Casco modeling project, data were collected from

the University of Maine Mooring C0201, Maine EPSCoR Mooring D0301 as well as Lobo 1 and Lobo 2 (http://umaine.edu/epscor/seanet/), and NOAA National Data Buoy Center Buoy 44007 (http://www.ndbc.noaa.gov) (see **Figure 1**). These datasets were used for the validation of additional test runs performed over the deployment periods of the buoys.

Time series validation of selected model output variables was performed. Only one station 8418150 (Portland, Maine) existed within the Saco and Casco domain with water level data for these two historic events. Tidal analyses were conducted using the "UTide" Matlab package to assess the model's ability at capturing tides and tidal residuals. **Figure 3a** and **d** compares the modeled SSH with the observations at the Portland station. **Figure 3b** and **e** compares the reconstructed tidal signals with UTide, which were removed from the raw signals to calculate the residuals (**Figure 3c** and **f**). After correcting for a constant negative bias of 2 feet detected between buoy records and NECOFS output, the modeled water level was able to capture the observed storm surge for the February 1978 event. However, the storm water level was lower than the observation in the first half of the storm window for the 2007 event. This was likely caused by the weaker predicted storm in the first half of the storm window wind seen in **Figure 2b**.

#### **Figure 3.**

*Comparison of the water level for the baseline simulation of the 1978 event (a–c) and the 2007 event (d–f) for the raw signals (a and d), tidal harmonics (b and e), and tidal residuals (c and f). Tidal constituents used in UTide include M2, N2, S2, K1, O1, NU2, and T2. Storm windows are indicated by vertical black lines.*

*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*

**Figure 4.**

*Comparisons of near-surface currents observed at buoy C0201 and modeled current for the April 2007 event. Negative velocities indicate westward (top) or southward (bottom) currents. The storm window is indicated by vertical black lines.*

Furthermore, current data was available at buoy C0201 for the 2007 event (**Figure 4**). The increase in westward velocity was revealed by the model, but at about half of the magnitude. The southward tendency was completely missed in the first half of the storm window again due to the errors in NECOFS-predicted wind direction. Discrepancies in modeled current output were examined by modifying the wind forcing. When the model run was repeated using the buoy-observed wind (red vectors in **Figure 2** and spatially uniform), the southward velocity in the first half of the storm window was improved, but the simulated currents deteriorated before and after the storm (not shown). Therefore, in this study we still used the simulations with NECOFS-predicted winds for the consistency between the surface and lateral boundary conditions because the open boundary condition adopted from the NECOFS was produced with the same set of meteorological forcing. As such, the 2007 event cannot be confidently referred to as a "storm scenario" with regards to modeled currents. However, the high discharge rates and availability of discharge data allowed us to utilize the April 2007 model runs as SLR simulations of a freshwater discharge event.
