Studies on water movements and sediments in Southern Lake Michigan : part 1[-3] ... / by John C. Ayers.

Volume Transport and Flushing Time
Although the dynamic height method of determining volume
transport is still subject to some unanswered questions, it remains to date the fastest and most feasible means of obtaining
such information where distances are great and/or where relative
wealth of indicative detail is needed.
Perhaps the best assessment is still that of Sverdrup,
Johnson and Fleming (1942, p. 394): "So many reservations have
been made that it may appear as if the computed currents have
little or no relation to the actual currents. Fortunately,
however, most of the assumptions made lead only to minor errors,
and currents can be correctly represented in the first approximation by means of the slopes of a series of isobaric surfaces
relative to one reference surface.'
To take the present volume transport results as first approximations is apparently within the validity of the method.
It is certainly compatible with the intent with which these preliminary investigations are presented.
Even as first approximations, the present results allow us
to take an initial step toward a more realistic determination of
the flushing time of the southern basin of Lake Michigan.
Large volumes of water cross the mid-lake sill, both into
and out of the southern basin. Water crossing the sill and
entering the southern basin joins with the inflows from the
rivers tributary to the southern basin in replacing the volume
of water that is contained in the basin at a given instant.
Continuity requires that the combined inflows be countermatched

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