Improved accuracy of short-distance measurement of water flow velocity using Pulse Boundary Model

Abstract

Salt tracer is one of the widely used shallow water velocity measurement methods. The Pulse Boundary Model method produces low velocity at short distances from the salt injection position. This study proposes a two-step approach to accu-rately estimate the flow velocity. Experiments were carried out under three flow rates of 12, 24, and 48 L min -1 and three slope gradients of 4, 8, and 12° at six measurement positions of 0.05, 0.3, 0.6, 0.9, 1.2, and 1.5 m from the solute injection positions. The new method obtains peak velocities that are 0.999 times those of the centroid velocities, indicating that either centroid or peak time can be equally used to measure flow velocity. The new method significantly improves measurement accuracy of flow velocity at short distances, as indicated by the almost equal measured velocities at all locations as those measured at longer distances. Velocities measured by the new method were significantly higher than those measured by the Pulse Boundary Model method or the centroid velocities measured by the traditional salt tracer method. In addition, the centroid and the peak velocities obtained by the new method correlates well to those by the traditional volumetric method. The velocities measured by the volumetric method were 0.79 (centroid velocity) and 0.78 (peak velocity) times of those estimated by the new and improved method. The results show that new and improved method provides an accurate and efficient approach in measuring shallow water flow velocity at short distances.