[1] Wetland-estuarine-shelf interaction processes in the Plum Island Sound and Merrimack River system in the Massachusetts coast are examined using the high-resolution unstructured grid, finite volume, primitive equations, coastal ocean model. The computational domain covers the estuarine and entire intertidal area with a horizontal resolution of 10-200 m. Driven by five tidal constituents forcing at the open boundary on the inner shelf of the eastern coast of the Gulf of Maine, the model has successfully simulated the 3-D flooding/drying process, temporal variability, and spatial distribution of salinity as well as the water exchange flux through the water passage between the Plum Island Sound and Merrimack River. The model predicts a complex recirculation loop around the Merrimack River, shelf, and Plum Island Sound. During the ebb tide, salt water in the Plum Island Sound is injected into the Merrimack River, while during flood tide, a significant amount of the freshwater in the Merrimack River is forced into Plum Island Sound. This water exchange varies with the magnitude of freshwater discharge and wind conditions, with a maximum contribution of ∼30%-40% variability in salinity over tidal cycles in the mouth of the Merrimack River. Nonlinear tidal rectification results in a complex clockwise residual recirculation loop around the Merrimack River, shelf, and Plum Island Sound. The net water flux from Plum Island Sound to the Merrimack River varies with the interaction between tide, river discharge, and wind forcing. This interaction, in turn, affects the salt transport from this system to the shelf. Since the resulting water transport into the shelf significantly varies with the variability of the wind, models that fail to resolve this complex estuarine and shelf system could either overestimate or underestimate the salt content over the shelf.
[1] The Integrated Ocean Observing System Super-regional Coastal Modeling Testbed had one objective to evaluate the capabilities of three unstructured-grid fully current-wave coupled ocean models (ADCIRC/SWAN, FVCOM/SWAVE, SELFE/WWM) to simulate extratropical storm-induced inundation in the US northeast coastal region. Scituate Harbor (MA) was chosen as the extratropical storm testbed site, and model simulations were made for the 24-27 May 2005 and 17-20 April 2007 (''Patriot's Day Storm'') nor'easters. For the same unstructured mesh, meteorological forcing, and initial/boundary conditions, intermodel comparisons were made for tidal elevation, surface waves, sea surface elevation, coastal inundation, currents, and volume transport. All three models showed similar accuracy in tidal simulation and consistency in dynamic responses to storm winds in experiments conducted without and with wave-current interaction. The three models also showed that wave-current interaction could (1) change the current direction from the along-shelf direction to the onshore direction over the northern shelf, enlarging the onshore water transport and (2) intensify an anticyclonic eddy in the harbor entrance and a cyclonic eddy in the harbor interior, which could increase the water transport toward the northern peninsula and the southern end and thus enhance flooding in those areas. The testbed intermodel comparisons suggest that major differences in the performance of the three models were caused primarily by (1) the inclusion of wave-current interaction, due to the different discrete algorithms used to solve the three wave models and compute water-current interaction, (2) the criterions used for the wet-dry point treatment of the flooding/drying process simulation, and (3) bottom friction parameterizations.
[1] The tidal motion in Mt. Hope Bay (MHB) and Narragansett Bay (NB) is simulated using the unstructured grid, finite-volume coastal ocean model (FVCOM). With an accurate geometric representation of irregular coastlines and islands and sufficiently high horizontal resolution in narrow channels, FVCOM provides an accurate simulation of the tidal wave in the bays and also resolves the strong tidal flushing processes in the narrow channels of MHB-NB. Eddy shedding is predicted on the lee side of these channels due to current separation during both flood and ebb tides. There is a significant interaction in the tidal flushing process between MHB-NB channel and MHB-Sakonnet River (SR) channel. As a result, the phase of water transport in the MHB-SR channel leads the MHB-NB channel by 90°. The residual flow field in the MHB and NB features multiple eddies formed around headlands, convex and concave coastline regions, islands, channel exits and river mouths. The formation of these eddies is mainly due to the current separation either at the tip of the coastlines or asymmetric tidal flushing in narrow channels or passages. Process-oriented modeling experiments show that horizontal resolution plays a critical role in resolving the asymmetric tidal flushing process through narrow passages. With a horizontal resolution of 50 m, FVCOM reproduces the eddy field that is in good agreement in the intensity and spatial scale with the current measurement data.
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