Finger Lakes history · waterway
Measuring Canadice Lake, and correcting the record
Rochester's engineers began measuring Canadice's outlet in 1903. The reports describe daily readings, unmeasured flow, and a unit-label error that survived in print for eleven years.
At Canadice Lake's outlet, someone read the depth of water over a weir each morning and again whenever the gates changed. A 1911 federal report describes this routine at the gaging station Rochester's engineers had established in February 1903.
The equipment included a standard thin-edged weir and additional rectangular gates, with the outflow controlled above the weir. The engineers used the Francis formula to calculate discharge and applied a velocity correction for larger flows.
The report also told readers where its figures came from. Rochester city engineer E. A. Fisher and principal assistant city engineer John F. Skinner had supplied the record. USGS stated that its own engineers had not verified it.
A later report shows how the measurements fitted into the water-supply system. The 1982 New York water-data report described Canadice outflow as diverted to Hemlock Lake for Rochester's supply, regulated by gates, and augmented by pumping.
Some water was not being counted. Intermittent flow over the spillway went unmonitored, the report said. That limited how accurately the adjusted record could represent natural runoff.
September 1982 marked the end of both records: the lake at station 04228950 and the outlet at station 04229000.
The same report corrected an error in the editions for 1971 through 1981. Changes in lake contents had been expressed in millions of cubic feet, but the printed labels had called them millions of cubic feet per second. The correction concerned the units attached to those figures.
The reports leave a record of more than readings. They identify the people who supplied the early data, explain how discharge was calculated, and acknowledge water the later measurements missed. Those details matter whenever the figures are used to describe the lake's past.
Source note
The station's February 1903 establishment, weir and gates, observation method, formula, and unverified Rochester provenance appear on printed page 82 of USGS Water-Supply Paper 264, Surface Water Supply of the United States, 1909, Part IV, St. Lawrence River Basin (1911). The station numbers, September 1982 discontinuation, diversion and regulation notes, spillway limitation, and unit correction appear on printed page 91 of Water Resources Data, New York, Water Year 1982, Volume 3 (USGS, 1983). This story paraphrases and cites the reports; it reproduces no scan, table, typography, or other source media.