Two Correct Methods for Installing Open Channel Flow Meters

Open channel flow meters are mainly used for flow measurement in reservoirs, rivers, water conservancy projects, farmland irrigation, and culverts. Since they primarily use the weir and flume method and the velocity-area method to calculate the flow rate of the water conveyance cross-section, their installation method directly affects the measurement results and accuracy.

Open channel flow measurement methods can be divided into two main categories based on the principle: the water level method and the velocity-area method.

1. The water level method requires the construction of water measuring structures, and its overall accuracy is not high. On one hand, when the head difference along the channel is small, the water measuring structure will cause head loss and affect the channel's water conveyance; on the other hand, if there are water retaining structures such as sluice gates downstream of the water measuring structure, submerged outflow will form at the structure, and the measurement accuracy will decrease significantly. The water level method is generally applied to channels with relatively small widths or small flow rates. When the channel width exceeds 1 meter, the cost of the water measuring structure increases considerably; at that point, if a water measuring structure is not built and the channel's water level-flow empirical relationship curve is used directly for flow measurement, the accuracy will be very low.

2. The velocity-area method does not require the construction of water measuring structures. It determines the flow rate by measuring the water-cross-sectional area (actually, the water-cross-sectional area is calculated indirectly from the measured water level) and the cross-sectional velocity, and it offers high accuracy without being affected by downstream backwater. Level measurement can be achieved by installing a level meter.