Connecticut Watersheds and Long Island Sound

Where Better Data Leads to Better Water Quality

Nutrient loadings from Connecticut’s watersheds play a decisive role in water quality across the state and in Long Island Sound, where excess nitrogen has long driven low-oxygen zones that affect fisheries, coastal communities, and interstate restoration efforts. Managing these risks starts with understanding them and requires models that reflect today’s data, conditions, and regulatory needs.

Working with the Connecticut Department of Energy & Environmental Protection, RESPEC has updated the Hydrologic Simulation Program–Fortran (HSPF) models for watersheds across the state that ultimately drain to Long Island Sound. These updates included incorporating current datasets, validating model performance, and configuring the models within RESPEC’s Scenario Application Manager (SAM) to support consistent scenario evaluation across watersheds.

We integrated the HSPF outputs into a Water Quality Analysis Simulation Program, creating a more complete picture of how nutrients move through watersheds and affect downstream waters. This integrated framework allows users to explore scenarios and compare management strategies. The framework also helps users understand cause-and-effect relationships, without losing sight of regulatory and operational realities.

A Defensible Foundation for Nutrient Management

The updated watershed models provide a clear basis for identifying nutrient sources, understanding transport mechanisms, and evaluating management options. For Connecticut, this work supports targeted, science-based actions to preserve and improve water quality in Long Island Sound, helping ensure the sound remains a resilient resource for ecosystems and the people who depend on them.