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 Long Island Sound Region


Long Island Sound Study partners are improving the technical tools to understand and manage the sources and impacts of nutrients on Long Island Sound, including:

  • Developing computer models that represent the physical, chemical, and biological processes on the land and water, and
  • Gathering data necessary to run and test models’ abilities to represent real-world conditions.

These models will greatly improve the understanding of nutrient pollution impacts as well as how to efficiently and cost-effectively reduce them. Multiple efforts are underway in both Connecticut and New York to develop modeling tools to better estimate the sources and amounts of nutrients generated in the Long Island Sound watershed, how the nutrients are delivered via rivers or groundwater to Long Island Sound and its embayments, and the effect these nutrients have on water quality. Learn about these efforts in the Connecticut, New York, and Systemwide Regional modeling web pages.

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