The common method of measuring flow through an open channel is to measure the height or HEAD of the liquid as it passes over an obstruction (a flume or weir) in the channel.

The velocity of a river or stream can also be measured using spot velocity meters such as turbine or doppler ultrasonics. There are many types of open channel flow meters

River Flow Meters can be permanent stream flow measurement devices . Also available are Portable Area Velocity Flow Meters which use Submersible Area Velocity Sensors .

These measure the average velocity of the water current directly without the need for time consuming flow profiling.

Knowing the average stream flow can significantly reducing the cost of installation and operation. They are built to withstand the outdoor usage.