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Instrumentation: Salt Dilution Flow Measurement: Automation and Uncertainty

Author(s): Gabe Sentlinger, John Fraser, Evan Baddock

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Keywords: tracer method; Automated Salt Dilution system; Signal to Noise Ratio; hydrometry


The tracer method of flow measurement is a relatively convenient and accurate method to measure discharge in turbulent streams and rivers where conventional current metering flow measurement is not suitable or safe. However, it can be difficult to obtain a full range of flow measurements for a hydrometric rating curve, especially at remote locations. Resources are often wasted visiting sites at similar flow conditions, and it can be difficult and dangerous to attempt flow measurements during peak flow events in active water courses. This paper describes and presents results from our Automated Salt Dilution system, AutoSalt. We also present the derivation of the uncertainty associated with the measurements. We have developed a system that can achieve acceptable results (<7% uncertainty) using as little as 100 g per m³/s of flow by increasing the Signal to Noise Ratio (SNR). We present results from installations in New Zealand, British Columbia, and Alberta and discuss how this work is aiding in the ongoing effort to establish a Standard Operating Protocol (SOP) for Salt Dilution in British Columbia, Canada


Year: 2019

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