Introduction

    The goal of the Great South Bay program is to gain a thorough understanding of the biogeochemistry of the Bay and its effect on pelagic and benthic communities.  An early focus of the modeling effort was on the impact that breaches might have on the ecology of the region as a result of changes in circulation, salinity, temperature, stratification, nutrient supply, productivity, bed-form and SAV, to name just a few of the potentially affected variables.  Modeling represents a potentially very useful tool for gaining a unified picture of how the various components of the system interact and are affected by alterations in the system.  Salinity is a keystone parameter in any estuarine modeling project as it is a conservative tracer intimately connected to critical features of the flow of water and dissolved constituents through the Bay system.  Without being able to accurately describe the salinity distribution throughout the Bay, not just at the inlets, there will be little prospect of understanding the sources and sinks of nutrients or making progress in the much more difficult task of modeling primary and secondary production.  Thus, we have attempted to carry out a staged effort to first replicate existing tidal and salinity conditions, concentrating in the back bay areas which are the most difficult to model, and then to see how these conditions are altered as a result of proto-type breaches in Fire Island Two potential breach locations, Old Inlet and Atlantique, have been examined by punching holes in Fire Island with cross-sections that are consistent with breach modeling studies carried out for the USACE.

Model Results

    A relatively new numerical circulation model, called the Finite Volume Coastal Ocean Model or FVCOM, can deal with the advection and dispersion of mass and material in the complicated geometries typified by coastal estuaries (Chen, Liu and Beardsley, 2003).  FVCOM is a three-dimensional primitive equation ocean model that conserves momentum, energy, heat, salinity and density, includes the Mellor-Yamada level 2.5 turbulent closure scheme, and matches a quadratic bottom drag with the interior through a logarithmic bottom boundary layer.  The 3-D solution is determined using a mode-splitting technique by which a 2-D external mode is updated at frequent intervals while the more slowly evolving internal mode is obtained less frequently.  By discretizing the integral form of the conservation equations within volume elements, it is easier to preserve mass and material than is possible with the usual finite difference techniques.  Thus the model is particularly suited to applications where the advection and mixing of salt, heat, nutrients and biological constituents are important issues.  In the FVCOM formulation the shape of the volume elements is arbitrary which means that the elements can be adapted to local conditions rather than attempting some global balancing act that minimizes the differences between the actual and grid geometries. At the same time, the model computes the fluxes between elements making the details of the dynamical balances and fluxes much more accessible than is possible with finite element models.