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Discharge Measurements under Ice
|Measurement at Methow River above Goat Creek|
For the assessment of the water resources of Washington State and the data disseminated through publications and the World Wide Web (Web), the USGS operates gages for the collection of gage height data and the determination of discharge. During most of the year, discharge measurements, described in WSP 2175 and OFR 03-490, are made by wading, from a bridge, or from a cableway, but when the river has frozen, an ice measurement is necessary to determine the flow beneath the ice, which is described in a policy memo.
The photos above show the technique used to measure flow beneath the ice. In the cross-section of the river 20-28 holes are augered through the ice. At each of these points the depth and velocity is measured, and the flow in the section is determined. The total discharge is then determined from the summation of the flow in all the sections. The flow can now be used to calibrate the stage-discharge rating during ice-effected periods and estimating flow during these periods.
Photo courtesy of Robert Drzmkowski, Spokane Field Office, November 2005.