Natural flow

The rate of water movement past a specified point on a natural stream. The flow comes from a drainage area in which there has been no stream diversion caused by storage, import, export, return flow, or change in consumptive use caused by man-controlled modifications to land use. Natural flow rarely occurs in a developed country.


Source: Corrosion-Doctors.org

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