Streamflow

The discharge that occurs in a natural channel. Although the term "discharge" can be applied to the flow of a canal, the word "streamflow" uniquely describes the discharge in a surface stream. The term "streamflow" is more general than the term "runoff", as streamflow may be applied to discharge whether or not it is affected by diversion or regulation.


Source: Corrosion-Doctors.org

Wikipedia:  https://en.wikipedia.org/wiki/Streamflow