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Freshwater Input

Fresh water was introduced directly into the model at grid cell locations representing the mouths of the Merrimack, Charles, Neponset and Mystic rivers as well as at the existing sewage effluent discharges at Nut and Deer Islands. In addition, input from the Penobscot, Androscoggin, Kennebec, and Saco Rivers were used to drive an adjunct model of the western Gulf of Maine that was used to help improve salinity open boundary conditions for the Massachusetts Bay model described here. (The western Gulf of Maine adjunct model is described in the open boundary condition chapter 2.9.) To indicate the relative importance of these sources, the mean flow during 1990 is shown in Table 2.1 and indicates that the Penobscot, Androscoggin/Kennebec and Merrimack River systems dominate the freshwater input to this region.

  
Table 2.1: Average freshwater inputs for the model during 1990. The scale factor is the amount that the gauged discharge was multiplied by to account for drainage area downstream of the gauge.

The Androscoggin and Kennebec Rivers are combined because they merge before discharge into the Gulf of Maine. The daily flows from the Neponset and Mystic Rivers were inferred by multiplying the daily flow from the Charles River by 0.431 and 0.195 respectively, factors determined by the ratio of the annual average.

Examination of the daily discharge over the three year simulation period shows that although the maximum discharge occurs during the spring of each year, there are secondary maxima in the fall (Figure 2.4). Fall 1990 in particular has unusually high discharge, almost as large as the preceding and following spring discharges.