The Determination of Minimum Flows for Sulphur Springs, Tampa

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DRAFT
Lastly, the effects of flow from Sulphur Springs on both the spring run and lower river are
strongly related to the rate of flow to the lower river from the Hillsborough River reservoir.
In recent decades there have been no flows to the lower river from the Hillsborough River
reservoir for about half the days each year on average. In the year 2000, the District
established a minimum flow of 10 cubic feet per second (cfs) for the Lower Hillsborough
River. The District also stipulated that alternate sources of water, including diversions from
Sulphur Springs, could be used to provide that flow.
As described in Chapter 3, the ecological benefits of flows from the spring to the river are
most critical when there would otherwise be no flow from the reservoir and minimum flows
to the lower river are in effect. Also, because water flowing from Sulphur Springs exceeds
potable water standards for certain constituents, it was assumed there would be little desire
to withdraw water from the spring when the reservoir is full and discharging. In
consideration of these factors, the District's analysis of minimum flows for Sulphur Springs
focused on periods of when there minimum flows to the lower river are in effect, rather than
on the historical seasonal characteristics of flow from the spring.
The District evaluated rates of flow from Sulphur Springs that would meet management
goals in the spring run and lower river during periods of minimum flow from the
Hillsborough River reservoir. Relying on data from a variety of sources, these goals were
based on analyses of the relationships of springflow to the ecological characteristics of the
spring run and lower river. As described in Chapter 4, these management goals are to:
1. Minimize the incursion of water from the Lower Hillsborough River into the upper
spring run
2. Maintain low salinity habitats in the Lower Hillsborough River
3. Maintain a thermal refuge for manatees near the mouth of the spring run during
winter months
These goals were developed to address the needs of biological communities in the spring
run and lower river that are sensitive to the effects of reduced flows. The purpose of goal
number one is to protect benthic macroinvertebrate populations in the upper spring run
from adverse effects resulting from the incursion of high salinity water from the lower
Hillsborough River during periods of low springflow. The purpose of goal number two is to
provide a salinity gradient in the lower river that includes low salinity habitats in order to
support the diversity of plant, invertebrate and fish populations that inhabit the lower river.
Goal number three provides for the thermal requirements of the Florida manatee, an
endangered marine mammal, that can be stressed or killed by cold water temperatures.
Within the context of these goals, the District used ecological indicators as parameters to
determine how well a minimum flow would meet each management goal. For goal number