Under-Ice: Computing Real-time Discharge

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Under-ice discharge is estimated using open-water reference hydrographs; however, the ratings for ice-affected sites are generally qualified as poor.

The U.S. Geological Survey (USGS), in collaboration with the Colorado Water Conservation Board, conducted a proof-of-concept to develop an alternative method for computing under-ice discharge using hydroacoustics and the Probability Concept.


Six conventional discharge measurements were collected concurrently with Probability Concept-derived discharges with percent differences (%) of -9.0%, -21%, -8.6%, 17.8%, 3.6%, and -2.3%.

This proof-of-concept demonstrates that riverine discharges can be computed using the Probability Concept for a range of hydraulic extremes (variations in discharge, open-water and under-ice conditions) immediately after the siting phase is complete, which typically requires one day. The Probability Concept and conventional methods such as index-velocity ratings offer water-resource managers and decision makers alternatives for computing real-time discharge for open-water and under-ice conditions.

Measuring discharge with hydroacoustics instrument under ice

Uplooking SonTek IQ Plus (in background) and TRDI V-ADCP (in foreground) and mounting bracket during ice-cover as captured on with a GoPro HERO3 on February 4, 2015 at the USGS streamgage 09064600 Eagle River near Minturn, Colorado, USA