The length of time required for an
estuary to exchange its water with the open
ocean.
If an estuary is small, net circulation will be rapid so the
flushing time will be short. This allows for the quick removal of wastes. On the other hand, an estuary with a slow flushing time risks the accumulation of
wastes and
pollutants.
I supposed you could also time a
toilet to determine its flushing time.