In order to measure discharge, we need to measure both the area of the cross section and the velocity of the water. (We'll measure the area later.) Remember that velocity has the units of speed which can be expressed as either feet per second, or meters per second.

In a stream, velocity is measured by using a velocity sensor attached to a wading rod. Below (left) is a picture of a wading rod with the velocity sensor attached. The sensor has a set of cups (or a propeller device) that spins in moving water. The faster the cups spin, the greater the stream's velocity.

Above John Stamm, a hydrologist, is holding a wading rod with a velocity sensor attached to the lower part of the rod. The sensor is connected by a wire to a digital display meter held by Professor Stamm.	Above is a close-up of the velocity sensor (top) and its digital display meter (bottom).