Streamflow - Measurement

Measurement

There are a variety of ways to measure the discharge of a stream or canal. A Stream gauge provides continuous flow over time at one location for water resource and environmental management or other purposes. For purposes that do not require a continuous measurement of stream flow over time, current meters or acoustic Doppler velocity profilers can be used. For small streams — a few meters wide or smaller — weirs may be installed. One informal method that provides an approximation of the stream flow termed the Orange Method or Float Method is:

1. Measure a length of stream, and mark the start and finish points. The longest length without changing stream conditions is desired to obtain the most accurate measurement.
2. Place an orange at the starting point and measure the time for it to reach the finish point with a stopwatch. Repeat this at least three times and average the measurement times.
3. Express velocity in meters per second. If the measurements were made at midstream (maximum velocity), the mean stream velocity is approximately 0.8 of the measured velocity for rough (rocky) bottom conditions and 0.9 of the measured velocity for smooth (mud, sand, smooth bedrock) bottom conditions.