DISCUSSION 
The two physical attributes giving the most insight into the type 
of circulation that exists in each system are the tidal prism (the volume 
of water added to the bay between low slack and high slack tides at the 
bay mouth) and average annual freshwater inflow volume. These attributes 
are convenient measures that are often used to represent tidal (mixing) 
and freshwater (stratification) influences, respectively. In situations 
where freshwater inflow dominates, conditions are favorable for formation 
of significant vertical density stratification with denser salty water on 
the bottom and less dense fresher water on the top. In conditions where 
tidal effects predominate, fresh and salt waters are well-mixed with 
little vertical variation of density. This distinction is important 
because the type of circulation likely to be found in an estuary is 
closely linked to its degree of stratification. 
Harleman and Abraham (1966) combined tidal prism and average 
freshwater inflow into an "estuary number" that can be used as a general 
index of the degree of stratification in bays and estuaries. Using this 
technique, an estuary number of 100 is a dividing point with values 
greater than 100 indicating increasingly well-mixed conditions and values 
less than 100 indicating increasingly stratified conditions. The 
stratification numbers for Sarasota, Tampa, and San Francisco Bays are 
about 1,000, 200, and 30, respectively. 
For well-mixed conditions --such as those found in Tampa and 
Sarasota Bays-- tidally averaged horizontal circulation patterns 
predominate (Figure 2). These patterns are caused by the interaction of 
tidal water motion with the bottom configuration and general shape of the 
estuary. For stratified conditions --such as in San Francisco Bay-- 
horizontal patterns can still exist, with the added complication of a 
vertical circulation (Figure 2). The vertical pattern is caused by the 
tendency for freshwater to override the denser saltwater. 
Little is known about the overall circulation pattern in Sarasota 
Bay. A few glimpses are available from the literature, however, that 
indicate existence of interesting circulation patterns. Fortune (1985, 
written communication) has reported on the paths of a series of drogues 
released in Sarasota Bay for a period of about 36 hours. Several drogues 
grounded in close proximity and others showed large net motion between 
tidal cycles. As part of a numerical modeling study of hurricane surge 
heights, Ross, Anderson, and Jerkins (1976) reported a nodal point in the 
central part of the bay. 
In contrast, circulation in Tampa Bay has been the subject of 
several studies, including those by Ross and Anderson (1972), Ghioto 
(1973, written communication). Cote (1973, written communication), Ross 
(1973), and Goodwin (1977, 1980, and 1987). Results from many of these 
studies have shown numerically that tidally averaged water motion in 
Tampa Bay is comprised of a series of horizontal circulation features 
that are thought to control the overall movement and distribution of 
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