The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
as manatees seek fresh water to drink. Use of the river varied from quick trips to the
spring run or dam spillway to extended stays in the river for two to three days. Manatees
were observed feeding on cattails and floating vegetation.
In August 1992, one of the tagged manatees was observed with nine others upstream
of the springs. One of the tagged females was observed in the river with her calf in the
summer of 1995 and then with a second calf in the fall of 1996. Although there are no
specific data for manatees giving birth in the Lower Hillsborough River, it may be a
calving area, as are other rivers in the Tampa Bay area.
Other documentation is recorded by FWC as part of a recent photo-identification
program, in which sites are visited and photographs are taken of manatee use. FWC
staff visited the spring on two dates in January and December of 2002, and on six dates
between January and March of 2003. Manatees were observed at Sulphur Springs on
half of these eight dates, with two animals observed on two dates and four animals on
one date. The staff report that the manatees generally congregate in the lower pool, but
have been observed in the upper pool. FWC staff visits the spring run at high tide
because manatees have trouble accessing the spring when tides are low due to shallow
water depths.
In summary, Sulphur Springs is not a major over wintering site for manatees in Tampa
Bay, as there are much larger and warmer thermal refuges available at the nearby
Apollo Beach power plant. However, manatees are observed in the lower river and
spring run during winter months and experience thermal benefits from the spring
discharge.
The seasonal thermal characteristics of the spring run and lower river are described in
the section below. Criteria that were used to evaluate the effects of removing or
diverting flow from Sulphur Springs on a thermal refuge for manatees in the Lower
Hillsborough River are described in Chapter Four. The results of thermal modeling
simulations in which various quantities of springflow were removed from, or re-routed
within, the river/spring system are presented in Chapter Five in support of the
determination of minimum flows for Sulphur Springs.
3.11.1 Thermal characteristics of Sulphur Springs pool and run
Water temperature data for the Sulphur Springs complex are available as monthly
values from the spring pool collected by the City of Tampa and 15 minute values
measured at three continuous recorders in the spring pool, the upper spring run, and
mouth of the spring operated by the USGS. The average water temperature for the
spring pool was 25 o C for 1991-2003 based on the monthly City data. The pool
temperature exhibited a slight seasonal pattern over this period (Figure 3-25), but the
monthly variations were very small (standard deviation = 0.4 o C).
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