The Corps Water Management System (CWMS) includes four interrelated models to assist with water management for the basin:
- GeoHMS (Geospatial Hydrologic Modeling Extension)
- ResSIM (Reservoir System Simulation)
- RAS (River Analysis System)
- FIA (Flood Impact Analysis)
The Connecticut River basin is the largest watershed in New England, extending from the northernmost part of New Hampshire to Long Island Sound. The watershed, which drains in a southerly direction, includes a small area of the Province of Quebec, and parts of New Hampshire, Vermont, Massachusetts, and Connecticut. Long and narrow in shape, it has a maximum length of about 280 miles and a maximum width of approximately 60 miles. The basin is bounded principally by the Androscoggin, Merrimack, and Thames River basins on the east and by the St. Lawrence, Hudson, and Housatonic River basins on the west.
Elevations range from sea level to over 5000 ft in the northern headwaters. Areas of well developed flood plains occur from Indian Stream in Pittsburgh, NH to Long Island Sound, the most extensive being in Massachusetts and Connecticut. The basin has a total drainage area of 11,250 square miles of which 114 mi2 are in Quebec, 3046 mi2 in New Hampshire, 3928 mi2 in Vermont, 2726 mi2 in Massachusetts, and 1436 mi2 in Connecticut.
The Connecticut River follows a general southerly course along the approximate centerline of its watershed for about 404 miles to its mouth on Long Island Sound at Saybrook, Connecticut. In the first 29 miles below its source, the river flows entirely within the State of New Hampshire, then for a distance of about 238 miles, between New Hampshire and Vermont, the western edge of the river forming the boundary; and finally across Massachusetts for 67 miles and Connecticut for 70 miles. The lower 60-mile reach of the river is tidal, with a mean tidal range during low river stages of 3.4 feet at the mouth, and about 1.2 feet at Hartford, 52 miles above the mouth. The fall in the river is about 2200 feet with the steepest portion averaging 30 feet per mile, occurring in the first 30 miles below the outlet of Third Connecticut Lake. From Wilder Dam, VT to the head of tidewater, 8 miles above Hartford, CT, the fall average about 2 ft per mile.
Wide and extensive flood plains are located at various reaches along the main stem. During major floods, these meadowlands become inundated to depths of 10 to 20 feet and act as large detention reservoirs which significantly reduce peak discharge at downstream locations. The most noteworthy are located in the following areas: the reach between West Stewartstown and Lancaster, NH; the 15-mile stretch between Woodsville, NH and Bradford, VT; in central Massachusetts between Montague City and Holyoke; and the extensive flood plains of Connecticut between Windsor Locks and Middletown.
There are important hydropower dams on the Connecticut River throughout its length. In the northern areas upstream of White River Junction are the Moore, Comerford, and Wilder projects; the Bellows Falls, Vernon, and Tuners Falls dams are located along the central reaches; and the Holyoke dam is in the southern portion of the basin.
The Connecticut River, in its southerly course to the ocean, is fed by numerous rivers and streams entering from the east and west. Rivers and streams on the western side of the basin are generally steeper and because the watersheds are steeper, flood runoff occurs more rapidly and peak contributions to Connecticut River flood flows have higher cfs/mi2 values than the eastern tributaries. The 15 largest tributaries, with watersheds larger than 200 mi2 and an aggregate area equal to 6517 mi2, or about 58 percent of the total basin area, include the Upper Amoonosuc River, Passumpsic River, Amoonosuc River, White River, Mascoma River, Ottauquechee River, Sugar River, Black River, West River, Ashuelot River, Millers River, Deerfield River, Chicopee River, Westfield River, and Farmington River.