Principle and method of flow measurement: channelmaster H-ADCP is a fixed acoustic Doppler flow automatic meter for real-time monitoring of flow velocity and flow in rivers and open channels produced by Teledyne Rd instruments. H-ADCP can be used as an independent real-time monitoring system for flow velocity and flow rate by connecting with computer through cable. H-ADCP can also be integrated with other instruments and equipment to form a water quality and quantity telemetry station. At present, channelmaster H-ADCP has three frequencies: 1200 kHz, 600 kHz and 300 kHz, which are suitable for sections with different widths. Channelmaster H-ADCP measures the flow rate by two horizontal ultrasonic probes and the water level by ultrasonic water level gauge, so as to complete the flow measurement and calculation. H-ADCP can be used for flow measurement by index velocity method. The index velocity method is to establish the correlation between the measured velocity (index velocity) of H-ADCP and the average velocity of river or open channel section, that is, to calibrate the system with the measured data to measure the flow. The specific comparison and calibration method is to use H-ADCP to measure the flow velocity (index flow velocity) and other methods to calculate the real flow of the river. According to the water level and the known large cross section, the flow area of the cross section can be calculated. The average flow velocity of the cross section can be obtained by dividing the flow by the flow area of the cross section; At this time, the velocity (index velocity) measured by H-ADCP corresponds to the average velocity of the section. Under different discharge and water depth, multiple sets of index velocity and section average velocity are obtained. Through regression analysis (using the least square method), the correlation (regression equation) between section average velocity and H-ADCP measured velocity (index velocity) can be established.