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Open-File Report 2011–1076

Prepared in cooperation with the Providence Water Supply Board

Streamflow, Water Quality, and Constituent Loads and Yields, Scituate Reservoir Drainage Area, Rhode Island, Water Year 2010

By Kirk P. Smith and Robert F. Breault

ABSTRACT

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Streamflow and water-quality data were collected by the U.S. Geological Survey (USGS) or the Providence Water Supply Board (PWSB), Rhode Island's largest drinking-water supplier. Streamflow was measured or estimated by the USGS following standard methods at 23 streamgages; 14 of these stations were also equipped with instrumentation capable of continuously monitoring specific conductance and water temperature. Streamflow and concentrations of sodium and chloride estimated from records of specific conductance were used to calculate loads of sodium and chloride during water year (WY) 2010 (October 1, 2009, to September 30, 2010). Water-quality samples also were collected at 37 sampling stations by the PWSB and at 14 monitoring stations by the USGS during WY 2010 as part of a long-term sampling program; all stations are in the Scituate Reservoir drainage area. Waterquality data collected by PWSB 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 2010.

The largest tributary to the reservoir (the Ponaganset River, which was monitored by the USGS) contributed a mean streamflow of about 39 cubic feet per second (ft3/s) to the reservoir during WY 2010. For the same time period, annual mean streamflows measured (or estimated) for the other monitoring stations in this study ranged from about 0.7 to 27 ft3/s. Together, tributary streams (equipped with instrumentation capable of continuously monitoring specific conductance) transported about 1,500,000 kilograms (kg) of sodium and 2,500,000 kg of chloride to the Scituate Reservoir during WY 2010; sodium and chloride yields for the tributaries ranged from 11,000 to 66,000 kilograms per square mile (kg/mi2) and from 18,000 to 110,000 kg/mi2, respectively.

At the stations where water-quality samples were collected by the PWSB, the median of the median chloride concentrations was 20.2 milligrams per liter (mg/L), median nitrite concentration was 0.002 mg/L as nitrogen (N), median nitrate concentration was 0.01 mg/L as N, median orthophosphate concentration was 0.06 mg/L as phosphorus, and median concentrations of total coliform and Escherichia coli (E. coli) bacteria were 93 and 16 colony forming units per 100 milliliters (CFU/100mL), respectively. The medians of the median daily loads (and yields) of chloride, nitrite, nitrate, orthophosphate, and total coliform and E. coli bacteria were 170 kg/d (73 kg/d/mi2), 11 g/d (5.3 g/d/mi2), 74 g/d (39 g/d/mi2), 340 g/d (170 g/d/mi2), 5,700 million colony forming units per day (CFU×106/d) (2,300 CFU×106/d/mi2), and 620 CFU×106/d (440 CFU×106/d/mi2), respectively.

First posted May 26, 2011

For additional information contact:
Director
U.S. Geological Survey
Massachusetts-Rhode Island Water Science Center
U.S. Geological Survey
10 Bearfoot Road, Northborough, MA 01532
(508) 490–5000
http://ma.water.usgs.gov

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Suggested citation:

Smith, K.P., and Breault, R.F., 2011, Streamflow, water quality, and constituent loads and yields, Scituate Reservoir drainage area, Rhode Island, water year 2010: U.S. Geological Survey Open-File Report 2011–1076, 26 p. (Also available at https://pubs.usgs.gov/of/2011/1076.)



Contents

Abstract

Introduction

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

Streamflow

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

Bacteria

Chloride

Nutrients

References Cited

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