The flow pattern resulting from a circular flume immersed in a rectangular channel is investigated. The circular flume consists of two PVC pipes. The larger diameter pipe is laid horizontally and the smaller pipe is fixed vertically inside it. The presence of the vertical pipe reduces the cross section of flow inside the horizontal pipe, creating a critical-flow condition. A gage is installed at the upstream side of the vertical pipe. The depth reading on the gage is directly related to the flow-rate and hence can be used as a measure for flow-rate. This mobile apparatus can be used on both lined and unlined canals. The circular shape of the flume fits to the natural shape of a furrow, reducing the possibility of lateral flow around the flume and makes it a convenient apparatus for measurement in furrows. The results showed variations between the real and the calculated flow-rates. These variations were due to the effect of streamlines curvature and were between 0.9% to 12.1%. Calibration equation of the flow-rate correction factor was developed taking into account the streamlines curvature effect.
Keywords: water measurement, flow measurement, canal discharge.