This paper presents a new type of water measuring device, the portable triangle-throated measuring flume, which is suitable for small flow conditions and easily to be manufactured and installed. The hydraulic performance of a prototype flume is tested under free flow and submerged outflow conditions at 9 flow rates such as 0.90, 1.44, 1.88, 2.36, 2.84, 3.36, 3.92, 4.57 and 4.90 L/s. The flume is located in a U-shaped channel that is similar to a field irrigation ditch in cross-section, and the water levels at 13 control sections are measured. The hydraulic performance variables such as water surface line, Froude number, critical inundation degree, and measurement accuracy were analyzed. There is a good exponential relationship between the flow rate and the upstream water depth with a correlation coefficient of 0.999 5. A formula for flow rate in terms of water depth is obtained by curve fitting under free and inundation flow conditions. Compared with the experimental flow rates, the average and maximum errors are smaller than than 5%. The change rules of Froude number are analyzed, and the specific position for the critical water depth is determined, which is downstream the throat within a distance of 334-355 mm from the flume inlet. The critical submergence of the long triangular-throated flume is stable, ranged from 0.80 to 0.86. The suitable range of flow range is 0.90-5.00 L/s for a single flume.
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