Drinking Water Quality Management Plan

295 Meridian Street
Groton CT 06340
(860) 446-4000

Watershed Information

Active Public Water Supply Watershed

Active Potential Public Watershed Map

The watershed of a particular point is the area surrounded by high spots, or divides, from which water drains or flows downhill to or past the point in question.

Surface water movement through a watershed begins with runoff flowing downhill as sheet flow, collection in small rivulets that erode shallow channels in the soil, and joining of small streams. These small streams receive additional runoff downstream and groundwater discharge from locally infiltrated precipitation, eventually merging where valleys meet.

The Connecticut Public Health Code defines a public drinking water watershed as an area that drains to a drinking water source.

The Great Brook watershed is approximately 16 square miles in size and is a direct drainage to Long Island Sound. The northern part of the watershed lies in the Town of Ledyard and the southern part of the watershed lies in the Town of Groton. Water flow trends in a general north to south direction in streams and waterbodies before ultimately reaching the coast. Approximately 6.5 million gallons per day (mgd) of the water in the watershed is removed 3.5 miles upstream from Long Island Sound at Groton Utilities' Poquonnock Reservoir for treatment and distribution to the water system.

The remaining flow in Great Brook passes through the downstream estuary that is bordered by a peninsula to the east where Bluff Point State Park is located and the Groton-New London Airport to the west.

Five active drinking water supply reservoirs serve the Groton Utilities system. Each of these reservoirs has several tributaries that drain the primary subwatersheds.

A diversion dam is located on Billings-Avery Brook. This diverts water from a 1.2 square mile drainage area via an open channel into Morgan Pond Reservoir, the most upstream of the water supply reservoirs. Morgan Pond Reservoir is located entirely within the Town of Ledyard. Water passing over the Morgan Pond Reservoir spillway flows into Ledyard Reservoir. The Ledyard-Groton municipal border runs through the Ledyard Reservoir, with roughly half of the water body in each town. Water that flows over the Ledyard Reservoir spillway flows via Great Brook into the terminal Poquonnock Reservoir.

From the east within the Town of Groton, Poheganut Reservoir flows into Smith Lake Reservoir, which in turn flows via open channel into the Poquonnock Reservoir. There is no direct hydrologic connection between the reservoirs to the east (i.e. Poheganut and Smith Lake Reservoir) and the upper watershed (i.e., Morgan Pond and Ledyard Reservoir).

Future Potential Public Water Supply Watersheds

Future Potential Public Watershed Map

Groton Utilities has identified future potential water supply sources in the Shewville Brook watershed, located within the Towns of Ledyard, Preston, and North Stonington; in the Joe Clark Brook watershed, located in the Town of Ledyard; and in the Haleys Brook watershed, located in the Towns of Groton and Ledyard.

The Shewville Brook watershed is approximately 17.3 square miles in size and drains to the Poquetanuck Brook, which meets the Thames River 11.2 miles upstream of Long Island Sound. The northern part of the watershed lies in the Town of Preston and the southern part lies in the Town of Ledyard, with a small part of the eastern watershed located in North Stonington. Water flow trends east to west in streams and waterbodies before ultimately reaching the Poquetanuck Brook.

In the eastern portion of the watershed, Lake of Isles Brook flows into Main Brook. The outflow from Avery Pond and Main Brook combine into Indiantown Brook, which also receives water from the Cedar Swamp in Preston before Indiantown Brook becomes Shewville Brook. Upstream of the future potential pump station location, Hewitt Brook and Myers Brook flow into Shewville Brook from the north.

The future potential pump station location on Joe Clark Brook would capture a two square mile watershed, including the upper two thirds of the entire Joe Clark Brook drainage. Flow generally flows southeast to northwest before entering Joe Clark Brook, which like Shewville Brook, drains to the Poquetanuck Brook. This watershed is located entirely within the Town of Ledyard.

The watershed upstream of the future potential Haleys Brook pump station is 7.3 square miles. The northern section of the watershed is located in the Town of Ledyard and the southern part in the Town of Groton. Haleys Brook flows northwest to southeast, with West Branch Brook and Red Brook joining from the north upstream of the future pump station location. Downstream of the pump station, Haleys Brook joins the Mystic River 3.2 miles upstream of Mystic Harbor, an embayment of Long Island Sound.

Working in conjunction with:

Town of Groton ConnecticutCity of Groton ConnecticutTown of Ledyard ConnecticutTown of Preston ConnecticutGroton Utilities