Water Quality Modeling

A Brief History in Long Island Sound

A grid domain of New York Harbor Observing and Prediction (NYHOPS) hydrodynamic modeling along with LIS Embayments (Points Represent the Center of Grid Cells; Selected Watersheds are In Yellow)

A scientific model is a mathematical, conceptual, or physical representation of a real phenomenon that might otherwise be difficult to observe or understand. These models can be used to explain or predict the behavior of a particular phenomenon and help make more informed management decisions. Mathematical models, in particular, are widespread throughout science. Climate change models are a prominent example. The Long Island Sound Study initiated modeling the late 1980s to simulate the impacts of nutrients on water quality in Long Island Sound (LIS). Called LIS 3.0, the model evaluated water quality conditions in 1988-1989. This model was used to support development by Connecticut and New York of the Total Maximum Daily Load Analysis to Achieve Water Quality Standards for Long Island Sound, approved by EPA in 2001.

The next major modeling effort was developed by the New York City Department of Environmental Protection of the System-Wide Eutrophication Model (SWEM) based on a much larger geographic domain. NYCDEP needed the model to support regional water quality management strategies for Combined Sewer Overflow controls and water quality evaluations of the New York-New Jersey Harbor, in addition to Long Island Sound. While SWEM provided useful insights that supported regional water quality management, it did not improve predictions of bottom-water dissolved oxygen concentrations in the Western LIS sufficiently to use it to evaluate the LIS TMDL. Instead, an independent review of SWEM recommended that a new modeling effort be initiated with a finer resolution grid for LIS.

Developing A New Generation of Models for the New York Harbor Region

The Long Island Sound Study and its partners have taken the initiative to develop a new generation of models to better describe dissolved oxygen concentrations as well as address new challenges such as warming temperatures, increasing precipitation and more development that can threaten the progress that has been made. In 2019, for example, the New York City Department of Environmental Protection (NYCDEP), with support from LISS, released a Request for Proposals (RFP) for the development of a new regional integrated model framework for water quality modeling in New York City waters (see nyc.gov website). These waters include Ling Island Sound, New York Harbor, and New York-New Jersey Bight (the waters along the Atlantic coast extending from Cape May in New Jersey to Montauk Point on the eastern tip of Long Island). This initial effort will include hydrodynamic and water quality models as well as a graphical user interface and decision support tool. It will build and improve upon the previous generation of models to guide future planning and management based on the best currently-available science. This RFP was developed following the production of a detailed report by a technical advisory committee composed of local and outside modeling experts. Work is expected to begin in summer 2020 and continue to 2024. Future projects to add ecological and related models are planned. 

Other Modeling in New York State

In addition to the New York City work, water quality modeling projects in New York are underway or have been recently completed around Long Island, including Long Island Sound.  The Long Island Nitrogen Action Plan (LINAP), a program initiated by the New York State Department of Environmental Conservation (NYSDEC), is identifying surface and groundwater sources of nitrogen, establishing nitrogen reduction endpoints, and developing nitrogen reduction plans in both Nassau and Suffolk Counties (see NYSDEC website). In 2019, Suffolk County released its detailed Subwatersheds Wastewater Plan, which established nitrogen load reduction goals and priorities for 191 sub-watersheds, including 27 which discharge into Long Island Sound (see Reclaim Our Water website). Related new efforts by the NYSDEC will model Nassau County sub-watersheds and potential hydrodynamic modifications on the north shore of Long Island to improve water quality. In addition, the United States Geological Survey (USGS) has undertaken a broader project to comprehensively delineate groundwater recharge areas, travel times, and outflows to Long Island streams and estuaries (see USGS website).

Water Quality Modeling in Connecticut

As part of Connecticut’s Second Generation Nitrogen Strategy the Connecticut Department of Energy and Environmental Protection (CTDEEP) will increase its focus on watersheds and update the statewide model of nutrient and sediment loads from rivers (see CTDEEP website).  Increased monitoring and estuarine modeling will also be conducted in the Niantic River Estuary and other selected embayments. These studies will build on previous University of Connecticut nitrogen loading modeling studies on 116 embayments around LIS and some the support for them comes from the LISS. USGS is also modeling groundwater flows in CT coastal areas as well as nitrogen loading to the Niantic estuary in collaboration with CTDEEP.

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