Surface water

The Westfield River basin drains about 517 mi2 and the Farmington River basin drains about 156 mi2 in Massachusetts. The Farmington River and the upper reaches of the Westfield River flow in narrow valleys bordered by steep slopes. Because of the steepness of the river banks, the low permeability of much of the surficial deposits, and large quantities of rainfall and snowmelt, the basins frequently have high runoff rates. Based on records from six long-term gaging stations, about 27 of the 47 in. of average annual precipitation become stream runoff.

Lakes and ponds in the basins were mostly created or enlarged by earthen dams, and are mostly larger than 10 acres. In the Westfield River basin, there are 78 lakes and ponds, 48 of which have an area of 10 acres or more. Only one lake, Cobble Mountain Reservoir in Blandford and Russell (1,135 acres), is larger than 500 acres. In the Farmington River basin, there are 47 lakes and ponds, 33 of which have an area of 10 acres or more. Two lakes are larger than 500 acres: Otis Reservoir (East Otis Reservoir, Clarks Pond) in Otis, which is 1,065 acres, and Colebrook River Reservoir in Sandisfield and Tolland, which is 760 acres. The Westfield River begins in Savoy in the northwestern corner of the basin and flows southward to southeastward to join the Connecticut River in West Springfield. Its major tributaries, the Middle Branch Westfield, West Branch Westfield, and Little Rivers, enter the Westfield River from the west.

The West Branch Westfield River is the largest totally uncontrolled river in the State. Overall, the Westfield River has a moderate gradient, averaging almost 29 ft/mi from its headwaters to the USGS streamflow-gaging station near Westfield, a distance of about 54 river mi.

Borden Brook and Cobble Mountain Reservoirs, located on the Little River in the southern part of the Westfield River basin, comprise the second largest water-supply storage system in the State. During 1985, an average of 37 Mgal/d of water was diverted from the Westfield River basin through this reservoir system to supply the Springfield water system.

The West Branch Farmington River begins in Becket in the northern part of the basin and flows southward into Connecticut, where it joins the Farmington River. The flow of the river is partially controlled by Otis Reservoir, but is more controlled just beyond the State line by Colebrook River Reservoir in Connecticut. Like the Westfield River, its major tributaries in Massachusetts, the Clam River and Sandy Brook, enter from the west. Overall, the West Branch Farmington River has a relatively steep gradient, averaging almost 68 ft/mi from its headwaters to the USGS streamflow-gaging station near New Boston, a distance of about 16 river mi.