Algorithm with improved accuracy for real-time measurement of flow rate in open channel systems

- Supercritical flow can be measured in an unconstrained channel using two liquid levels.
- With two measured liquid levels, accurate flow rate can be determined in an accelerating flow.
- Accuracy of flow measurement with a Venturi channel can be improved to ± 0.8%.
- Unsteady state flow rates can be estimated with a reasonable accuracy of about ± 5.6%.

Most methods for flow rate measurement in open channels usually have low accuracy over a range of flow rates due to varying fluid properties, flow conditions and channel length. This paper suggests an algorithm to improve on the accuracy of flow rates computed based on hydraulic structure and slope-hydraulic radius methods. A model for determining flow rates in accelerating flows is also developed. In the proposed algorithm, the parameter used for adapting the flow rate models is obtained by comparing the measured fluid depth with the depth simulated based on the one-dimensional Saint Venant equations. The results show that an improvement from ± 2.3% to ± 0.8% accuracy in the flow rate measurement using the Venturi flume method could be achieved. In unsteady state flow in a straight-run channel, the results based on flow simulation also show possibility of achieving accurate computation over a wide range of flow rates.