Comparison of Estimates of Uncertainty of Discharge at US Geological Survey Index-Velocity Gages on the Chicago Sanitary and Ship Canal, Illinois

Abstract

Estimates of uncertainty of discharge at time scales from 5 minutes to 1 year were obtained for two index-velocity gages on the Chicago Sanitary and Ship Canal (CSSC), Ill., instrumented with acoustic velocity meters (AVMs). The velocity measurements obtained from the AVMs are corrected to a mean channel velocity by use of an index-velocity rating (IVR). The IVR is a regression-derived relation between the AVM velocity estimates and those obtained using acoustic Doppler current profilers (ADCPs). The uncertainty estimation method is based on the firstorder variance method, but the AVM velocity error is estimated from an empirical perspective, using the statistics of the IVR regression. It is not clear whether to include the standard error of the IVR regression ( ) in the discharge uncertainty. At the 5-minute time scale when is included, has the dominant contribution to the discharge uncertainty, and the discharge uncertainty (expressed as the standard deviation of the discharge estimate) is about 5 m 2 e σ 2 e σ 2 e σ