Weeki Wachee River System Recommended Minimum Flows and ...

7.2 Manatee Approach
Establishing a thermal MFL required a number of steps in order to adequately portray
critical conditions. The steps are described in detail in Impacts of Withdrawals on the
Thermal Regime of the Weeki Wachee River 23 (ATM 2007) and are summarized herein.
An adequate thermal refuge results from sufficient discharge of warm water, appropriate
depth and access. Tide stage can greatly affect the size of refuge as cold Gulf water is
transported further inland with higher than normal tides. The thermal offset required is a
function of the temperature differential between the colder Gulf waters and the warmer
spring discharge.
While there is an adequate record of air temperature at Weeki Wachee, there is no
long-term continuous record of water temperature in Weeki Wachee. The available
continuous record of water temperature is limited to 2003-2005 at Bayport, but air
temperature extends from 1970 to 2005 at Weeki Wachee. In order to evaluate a
longer period, a regression was developed from air temperature to predict water
temperature at Bayport. Figure 7-1 summarizes the relationship developed between air
temperature and water temperature which allows an extended prediction 24 of water
temperature.
Figure 7- 1
Weeki Wachee Air Temperature vs. Bayport Water Temperature
T Water = 7.73+ 0.735 * (3-day average air temp)
n = 711, r 2 = 0.90
23 Available at http://www.swfwmd.state.fl.us/documents/
24 Some temperatures were predicted from air temperatures which were below the regression domain.
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Proposed Minimum Flows and Levels for Weeki Wachee River
Technical Approach Page 101 of 164