The flow measurement system operates by transmitting an acoustic wave signal from its transducer towards the liquid being monitored. The reflected signal or echo is received by the transducer and processed. The time between transmission of the acoustic signal and reception of the echo is measured, and using the speed of sound through air, the distance from the transducer to the liquid level is calculated. Flow through the channel or structure is then calculated from the level measurement and the user entered properties of the channel.