Experimental evidence on the performance of rating curves for continuous discharge estimation in complex flow situations

Abstract

The paper presents various aspects of monitoring streamflows with stage-discharge (HQRC) and index-velocity (IVRC) based ratings at a non-ideal gaging station with emphasis on their reliance during fast-varying unsteady flows. For this purpose, the paper analyzes data obtained from customized experiments whereby the flow phases are tracked as they develop during flow transitions. The analysis compares discharges obtained from HQRC and IVRC ratings with those directly measured with Acoustic Doppler Current Profilers (ADCP) and a flowmeter set in the housing of the turbines that release the flow in the downstream channel. It is found that during steady flows, both HQRC and IVRC methods perform within the widely accepted ±5% thresholds recommended for streamflow gaging despite that the site considerably deviates from the guidelines for gaging site selection. For unsteady flows, the performance of the IVRC is considerably better than HQRC. Attempts are made to complement the typical statistical analysis used for assessing the quality of discharge estimates provided by the ratings with insights into flow characteristics that deteriorate the quality of the flow estimates passing through the stations.