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Open-File Report 2010–1045

Prepared in cooperation with the
Providence Water Supply Board and the
Rhode Island Department of Environmental Management

Streamflow, Water Quality, and Constituent Loads and Yields, Scituate Reservoir Drainage Area, Rhode Island, Water Year 2005

By Robert F. Breault and Jean P. Campbell


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Streamflow and water-quality data were collected by the U.S. Geological Survey (USGS) or the Providence Water Supply Board, Rhode Island’s largest drinking-water supplier. Streamflow was measured or estimated by the USGS following standard methods at 23 streamgage stations; 10 of these stations were also equipped with instrumentation capable of continuously monitoring specific conductance. Streamflow and concentrations of sodium and chloride estimated from records of specific conductance were used to calculate instantaneous (15-minute) loads of sodium and chloride during water year (WY) 2005 (October 1, 2004, to September 30, 2005). Water-quality samples were also collected at 37 sampling stations in the Scituate Reservoir drainage area by the Providence Water Supply Board during WY 2005 as part of a long-term sampling program. Water-quality data are summarized by using values of central tendency and are used, in combination with measured (or estimated) streamflows, to calculate loads and yields (loads per unit area) of selected water-quality constituents for WY 2005.

The largest tributary to the reservoir (the Ponaganset River, which was monitored by the USGS) contributed about 30 cubic feet per second (ft3/s) to the reservoir during WY 2005. For the same time period, annual mean streamflows1 measured (or estimated) for the other monitoring stations in this study ranged from about 0.42 to 19 ft3/s. Together, tributary streams (equipped with instrumentation capable of continuously monitoring specific conductance) transported about 1,300,000 kilograms (kg) of sodium and 2,000,000 kg of chloride to the Scituate Reservoir during WY 2005; sodium and chloride yields for the tributaries ranged from 13,000 to 77,000 kilograms per square mile (kg/mi2) and from 19,000 to 130,000 kg/mi2, respectively.

At the stations where water-quality samples were collected by the Providence Water Supply Board, the median of the median chloride concentrations was 25.3 milligrams per liter (mg/L), median nitrite concentration was 0.002 mg/L as N, median nitrate concentration was 0.02 mg/L as N, median orthophosphate concentration was 0.07 mg/L as P, and median concentrations of total coliform and Escherichia coli (E. coli) bacteria were 23 and 15 colony forming units per 100 milliliters (CFU/100 mL), respectively. The medians of the median daily loads (and yields) of chloride, nitrite, nitrate, orthophosphate, and total coliform and E. coli bacteria were 230 kg/d (93 kg/d/mi2), 16 g/d (6.1 g/d/mi2), 150 g/d (71 g/d/mi2), 530 g/d (250 g/d/mi2), and 1,500 million colony forming units per day (CFU×106/d) (630 CFU×106/d/mi2) and 420 CFU×106/d (290 CFU×106/d/mi2), respectively.

1The arithmetic mean of the individual daily mean discharges for the year noted or for the designated period.

First posted June 1, 2010

For additional information contact:
U.S. Geological Survey
Massachusetts-Rhode Island Water Science Center
42 Albion Road, Suite 107
Lincoln, RI 02865

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Suggested citation:

Breault, R.F., and Campbell, J.P., 2010, Streamflow, water quality, and constituent loads and yields, Scituate Reservoir drainage area, Rhode Island, water year 2005: U.S. Geological Survey Open-File Report 2010–1045, 24 p. (Also available at




Streamflow Data Collection and Estimation

Water-Quality Data Collection and Analysis

Data Collected by the U.S. Geological Survey

Data Collected by the Providence Water Supply Board

Estimating Daily, Monthly, and Annual Loads and Yields


Water Quality and Constituent Loads and Yields

Sodium and Chloride Loads and Yields Estimated from Specific-Conductance Monitoring Data

Physical and Chemical Properties and Daily Loads and Yields Estimated from Data Collected by the Providence Water Supply Board

Physical and Chemical Properties

Constituent Concentrations and Daily Loads and Yields




References Cited

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