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ICE EFFECTS ON STREAMFLOW
The formation of ice on rivers can cause discharge values to appear unusually high. Display of these erroneous discharge data may result in improper assessment of flow conditions and misuse of the data. For this reason, display of discharge values for streams significantly affected by ice may be disabled from view. Display of discharge data will resume when ice conditions are no longer present. Discharge values for streams minimally affected by ice will continue to be displayed. Flows for streams with these conditions appear to increase during the night and decrease to near-base-line conditions around midday. To estimate the correct discharge for these streams, use the flow rate that corresponds to the bottom of the discharge curve, rather than the peak that corresponds to the top of the curve. Note that this method of estimation is possible only when no surface runoff is occurring. Daily mean discharges for periods of both significant and minimal ice-effect will be estimated and published in the Annual Water-Data Report for the water year in which they occurred.
LOCATION--Lat 42° 38’45", long 71°
17’56", Middlesex County, Hydrologic Unit 01070002, on right
bank at Lowell, 1,100 ft downstream from Concord River.
DRAINAGE AREA--Total above gage, 4,635 mi2; net above gage, 4,421 mi2—excludes 214 mi2 for use of Boston metropolitan district and city of Worcester.
PERIOD OF RECORD--Discharge: June 1923 to current year.
Water-quality records: Water years 1954, 1966–74, 1999.
GAGE--Data Collection Platform with satellite telemeter. Datum of gage is 5.18 ft above National Geodetic Vertical Datum of 1929. Prior to Mar. 7, 1934, at Boot Mills, 1,800 ft upstream and 700 ft above mouth of Concord River, in same gage pool and at same datum; gage-height record (provided by Proprietors of the Locks and Canals on Merrimack River) was indicative of flow including that of Concord River.
REMARKS--Daily discharge includes water released from 210 mi2 in basins of Sudbury and Nashua Rivers and Lake Cochituate. Flow regulated by powerplants, by Franklin Falls Reservoir since 1942, and by Squam, Newfound, Winnipesaukee, Winnisquam, and other lakes and reservoirs upstream.
COOPERATION BY--Massachusetts Department of Conservation and Recreation, Office of Water Resources.
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Value May 20