by the 12-year average salinity distribution of Hillsborough Bay 
(Figure 10). 
Assuming that this generalized, tidal 1y averaged flow concept is 
correct, Goodwin (in press) estimated how circulation increases between 
1880 and 1985 may have changed the average time needed for suspensed or 
dissolved material to transit from the head to the mouth of Hillsborough 
Bay. The transit time in 1880 is estimated to have been about 60 days. 
Due to increased circulation, the transit time in 1985 is estimated to 
have been about 30 days. This indicates that Hillsborough Bay may now be 
able to flush itself of waterborne material having a landward source in 
about half the time that it took in 1880. 
It is likely that increased flushing has also caused an increase 
in bay salinity because tributary freshwater inflow to Hillsborough Bay 
can also be conveyed through the bay in about half the time that it took 
in 1880. The salinity increase in the bay from 1880 to 1985 due to 
increased flushing is computed to be in the range of 2 to 3 parts per 
thousand. Reductions in Hillsborough River discharge (Flannery, this 
report) probably have also contributed to an increase in bay salinity, 
but this effect has not been quantified. 
In spite of the circulation information available for the Tampa 
Bay system, much more remains unknown. Questions regarding the effects 
of wind are unanswered for both Tampa and Sarasota Bays. Are wind 
effects dominant or do they represent short-term perturbations on the 
tide-induced circulation? Another unanswered, circulation-related 
question that has a large bearing on overall flushing rates and the 
concentration of waterborne constituents is the mechanism of exchange 
between bay and gulf waters. Of the water exiting Tampa and Sarasota 
Bays during ebb tide, what percentage returns during the next flood tide? 
These and other Tampa Bay questions are addressed in a comprehensive 
management plan, as requested in Florida’s Surface Water Improvement and 
Management Act of 1987. Similar answers are being sought for Sarasota 
Bay through a federally sponsored estuarine initiative administered by 
the U.S. Environmental Protection Agency. 
62 
