Physical Setting And Hydrology

The Connecticut River forms the border between Vermont and New Hampshire and bisects west-central Massachusetts and central Connecticut. The topography of the Connecticut River's 11,250-square-mile watershed varies from the rugged terrain of

Figure 5-2 Location map for Lower Connecticut River Basin. (River miles shown are distances from Long Island Sound.)

the White Mountains in New Hampshire and the rounded hills and mountains in Vermont and Massachusetts to the lowlands of the floodplains along the river's banks in Massachusetts and Connecticut. Rising in the semi-mountainous area of northern New Hampshire, the Connecticut River drops more than half of its 2,650 feet in elevation in the first 30 miles of its course. The river is tidally influenced from Hartford to Long Island Sound (Figure 5-2).

Long-term trends in summer streamflow from the USGS gage at Thompsonville, Connecticut, shown in Figure 5-3, illustrate the interannual variability of discharge during the critical summer months. Seasonal flow conditions reflect the long, cold winters and the relatively short summers characteristic of New England. High flows are generally experienced in the spring (March-May), corresponding to large snow-melt events (Figure 5-4). Low flows occur during the summer months. In the past, flow regulation for hydropower production at Holyoke Dam (Massachusetts) periodically reduced flows in the Connecticut River to a minimum of near zero, but minimum re-

Figure 5-3 Monthly trends of mean, tenth, and ninetieth percentile streamflow for the Connecticut River at Thompsonville, Connecticut (USGS Gage 01184000), 1951-1980. Source: USGS, 1999.

Figure 5-4 Long-term trends in mean, tenth, and ninetieth percentile streamflow in summer (July-September) for the Connecticut River at Thompsonville, Connecticut (USGS Gage 01184000). Source: USGS, 1999.

POPULATION, WATER, AND LAND USE TRENDS 203

lease requirements have been established to maintain the summer low flow at a higher level. Currently, the flow is regulated by a number of headwater lakes and reservoirs, as well as power plants, with a combined usable capacity of 107 billion cubic feet (USGS, 1989) at Thompsonville, Connecticut. The 7-day, 10-year low flow (7Q10) discharge at Thompsonville is 2,200 cubic feet per second (cfs). The minimum recorded daily discharge was 519 cfs on September 30, 1984, below the Holyoke Dam and 968 cfs on October 30, 1963, at Thompsonville, Connecticut (USGS, 1989).

POPULATION, WATER, AND LAND USE TRENDS

The population density in the Connecticut River Basin generally increases from the north to the south. Approximately 85 percent of the river basin's residents live in Massachusetts and Connecticut. Approximately 1.1 million people live in Connecticut municipalities adjacent to the river; the largest city, Hartford, had a 1990 estimated population of 139,739 (CSDC, 1991). The Connecticut River case study area includes a number of counties identified by the Office of Management and Budget (OMB, 1999) as Metropolitan Statistical Areas (MSAs) or Primary Metropolitan Statistical Areas (PMSAs). The Hartford, Connecticut, MSA and three Connecticut counties, Fairfield, Middlesex, and Tolland, are included in this case study. Figure 55 presents long-term population trends (1940-1996) for the three counties. From 1940 to 1996, the population in the Connecticut River case study area about doubled (Forstall, 1995; USDOC, 1998).

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