Considerations on discharge estimation using Index-Velocity Rating Curves

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Marian Muste, Zhengyang Chen, Peter Vidmar, Jim Hulme

Thursday 2 july 2015

8:30 - 8:45h at Africa (level 0)

Themes: (T) Special session, (ST) Acoustic monitoring of flow, turbulence and river discharge

Parallel session: 10F. Special session: Acoustic monitoring of flow, turbulence and river discharge

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Horizontal- Acoustic Doppler Current Profilers (H-ADCP) in conjunction with the index-velocity method are extensively used for replacing the conventional stage-discharge for computing continuous records of discharge in natural streams. The index velocity-velocity is recommended over the stage-discharge method for inland river gaging sites where backwater or unsteady flows can occur (e.g., confluences, in the vicinity of hydraulic structures). Previous comparisons of discharge estimates provided by stage-discharge and index-velocity Rating Curves with simultaneous transect ADCP measurements in unsteady flows conditions suggest that the magnitude of the deviations from the direct measurements are much reduced for index-velocity RC (IVRC) compared to stage-discharge RC (HQRC). This is mainly attributable to the fact that IVRC relies on two direct measurements (stage and velocity along a cross section) vs just one direct measurement in HQRC, hence the flow dynamics are better captured with the first measurement approach. This paper reports new experimental evidence on discharge determination downstream from a dam with frequent and rapid flow changes as documented with four alternative real-time discharge monitoring methods. Findings inferred from the new set of measurements in steady and unsteady flows complement those from prior investigations and offer additional insights into the potential causes of the differences between various discharge measurement methods.