1 In contrast, velocities of streamflow generally are measured in feet per second. 2  A velocity of 1 foot per second equals about 16 miles per day. 3  The low velocities of ground-water flow can have important implications, particularly in relation to the movement of contaminants. A velocity of 1 foot per day or greater is a high rate of movement for ground water, and ground-water velocities can be as low as 1 foot per year or 1 foot per decade.