To discourage plugging of the passageway connecting the stilling well to the channel, a small
flow rate of clean water may be introduced into the well. This forms a constant purge flow into the
channel, flushing out debris that might otherwise find its way into the connecting passageway to
plug it up. Note how the purge water enters the stilling well through a submerged tube, so it does
not cause splashing on the water’s surface inside the well which could cause measurement problems
for the ultrasonic sensor