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 Housatonic River Basin comprises an area of 1,949 square miles and is located in the western portion of Massachusetts and Connecticut and eastern New York. The basin is roughly elliptical in shape, oriented in a north – south direction with a maximum length and width of 98 and 35 miles, respectively. It is a hilly basin with forested uplands and cleared valleys. Elevations vary from mean sea level (msl) to 2,620 feet msl along the northern divide. There are numerous lakes and ponds scattered throughout the basin which have a modifying influence on minor floods, but generally have little effect on major floods. There is considerable valley storage on the main stem Housatonic River between Great Barrington and Falls Village, which has a significant effect in desynchronizing flood-flows from the upper watershed. The coordinated flood control plan for the basin, described in the Housatonic River Basin Master Manual of Water Control, includes seven dams and five local flood protection projects. Although the title Master Manual of Water Control is the Housatonic River Basin, all the flood control projects are located within the Naugatuck River watershed, the most significant tributary of the Housatonic River, having major damage centers with urban, highly developed areas. Of the seven dams, five are owned and operated by the Corps of Engineers and two are owned by the Connecticut Department of Environmental Protection (CT-DEP). The five Corps dams consists of three fully staffed dams with gated outlet works (Thomaston, Black Rock, and Hop Brook Dams), and two unstaffed with ungated, fixed opening outlet works, considered self-regulating (Hancock Brook and Northfield Brook Dams). The two dams owned by CT-DEP are also self-regulating dams (East Branch and Hall Meadow Dams). The Naugatuck River is the largest and most important watershed of the Housatonic River, and thus the CWMS modeling effort focused primarily on the Naugatuck River Watershed.
The general flow of the Naugatuck River Watershed is southerly through the communities of Torrington, Thomaston, Waterbury, Naugatuck, Beacon Falls, Seymour, and Ansonia to Derby where it discharges into the Housatonic River, 12 miles above its mouth. The watershed of the Naugatuck River is located primarily within the boundaries of Litchfield and New Haven Counties, with a small portion extending into Hartford County. The Naugatuck River watershed has a maximum length and width of approximately 50 and 12 miles respectively, and drainage area of 312 square miles. It has a rather uniform slope of about 14 feet per mile between the headwaters at Torrington and tidewater in Derby, Connecticut. The river valley is narrow with rocky hills rising on either side making it conducive to rapid runoff with little to no moderating effect on flood flows. Elevations vary from maximum of 1,625 feet msl on Dennis Hill in Norfolk along the northern divide to approximately 5 feet at the mouth. Its several relatively short and steep tributaries are conducive to rapid runoff. Major tributaries are the East and West Branches, Leadmine Brook, Branch Brook, Hancock Brook, Mad River, Meadow Brook, Little River, Bladdens River and Beaver Brook.