Byflow

Runoff measurements tended to be slightly inaccurate due to underflow or byflow of small but rapid streams flowing in solid or pebbly mountainous channels.

Source: wiktionary

The internal overflow steel dam should be used for this purpose to allow byflow. With a closed-type riser it should be possible to couple the suction pipe to the hydrant and, of course, no byflow arrangement is required.

Source: wiktionary

Why not cut St. Leonard's-on-Sea, which is a confounded Hastings circuited by a byflow of parade, and come straight here to Bournemouth — really one of the prettiest of all the English Sea-Sides, with pines growing to the sands.

Source: wiktionary

In other words, in the main flow it is the physical variable itself, the "substance", that matters; in the by-flow it is just information.

Source: wiktionary