As part of Connecticut’s Second Generation Nitrogen Strategy, the Connecticut Department of Energy and Environmental Protection (CTDEEP) will be modeling watershed surface and groundwater flows and nutrient loading, along with estuarine modeling of the Pawcatuck River, Niantic River Estuary, and other selected embayments.
A watershed model simulates the movement of water, sediment, and pollutants over the landscape and draining to a waterbody. The model first represents the movement of water, starting with precipitation and snow melt. In pervious areas (with natural vegetation) water may evaporate, run off on the surface, or infiltrate and move through the soil or ground water. In impervious areas (roads, roofs) water does not infiltrate, so only evaporation and surface runoff are considered. The model next simulates the movement of particles, which often carry pollutants. This is done through erosion in the pervious area, and washoff of particulate matter in the impervious area. Finally, the model represents movement of pollutants, in association with either water or particulate matter.
In 2002, the Connecticut Department of Energy and Environmental Protection (CTDEEP) developed the Connecticut Watershed Model (CTWM). This statewide watershed model was developed as a tool to evaluate nutrient sources and loadings, including nitrogen, phosphorus, and organic carbon, within each of six nutrient management zones and assess their delivery efficiency to LIS. The model supported initial efforts to manage watershed nutrient sources, but the final report identified deficiencies that if addressed would improve the accuracy and utility of the model moving forward. Work is now underway to address deficiencies in the 2002 effort by updating the CTWM with the following improvements:
Groundwater discharge to Long Island Sound along the north shore coast of Long Island Sound is small relative to discharge from the major rivers but is locally an important nutrient source to coastal embayments. The US Geological Survey (USGS), in cooperation with CTDEEP, is developing a regional groundwater flow model of coastal Connecticut as well as adjacent areas of Rhode Island and New York (excluding Long Island). The model will simulate groundwater budgets, groundwater travel time distributions, and will estimate groundwater loading to receiving waters (rivers or directly to Long Island Sound).
USGS is working to calibrate the groundwater model over two years. In 2020 USGS is refining Niantic River watershed modelling to simulate groundwater nitrogen loading to freshwater receptors (mainly rivers) and the coastal embayment. In 2021, USGS will extend the nitrogen model to the entire model domain. CTDEEP will use the calibrated regional model to better understand groundwater flow systems in coastal areas on the north shore of Long Island Sound, including quantitative information such as groundwater budget components at the watershed- and model-domain scales and travel times to freshwater and coastal receptors.
The work will include:
USGS and CTDEEP expect that the outputs from the project will also provide an estimated time context for management scenarios that have an impact on nitrogen in LIS. USGS could assign travel times from recharge to discharge for different land covers in the present, past, or future to understand the nitrogen discharge input function with time or under future management scenarios. These outputs combined will help CTDEEP prioritize nitrogen reduction actions where groundwater nitrogen discharges are greatest.
The groundwater flow model and supporting data will be publicly available and study results will also be presented on the project web page.
Connecticut continues progress on its Second-Generation Nitrogen Strategy, which prioritizes embayments for further study and the preparation of protection or restoration plans.
In 2017, CTDEEP prioritized the following eight embayment complexes (some complexes include multiple embayments):
CTDEEP has initiated monitoring and modeling efforts in the Pawcatuck River Estuary and Little Narragansett Bay; CTDEEP is also conducting a data synthesis and modeling effort on the Niantic River Estuary. These efforts will serve as a framework for CT DEEP to apply in other priority embayments. In 2020 CTDEEP is initiating monitoring and modeling of Mystic River and Norwalk Harbor. In general, embayment modelling will include: