The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
CHAPTER 4
TECHNICAL APPROACH FOR DETERMINING MINIMUM FLOWS FOR
SULPHUR SPRINGS
4.1 Overview
The chapter presents the District's approach for determining minimum flows for Sulphur
Springs. As discussed in Chapter 3, flows from Sulphur Springs provide important
ecological functions to both the spring run and the Lower Hillsborough River. The
District's approach to establishing minimum flows for Sulphur Springs therefore
considered potential impacts to natural systems in both the spring run and lower river.
The resource characteristics and management goals upon which the minimum flows for
Sulphur Springs are based are described below. The results of empirical data analyses
and mechanistic modeling that were used to determine the minimum flow are described
in Chapter Five, along with the proposed minimum flows.
4.2 Consideration of structural alterations to the determination of minimum
flows
In keeping with directives provided by Florida Statutes (373.0421(1a) F.S., the District
took into consideration structural alterations to the spring and river system in the
determination of minimum flows. One of the most important alterations is that the spring
pool is enclosed by a circular concrete wall that extends about three feet above the land
surface. Under normal operations, the pool is hydraulically isolated from the spring run
and is not used as habitat by aquatic biota in the spring run or lower river. As a result of
this physical isolation, the determination of minimum flows for Sulphur Springs did not
evaluate the ecology of the spring pool proper, but instead focused on the functions of
flow from the pool on the downstream biological communities in the spring run and
lower Hillsborough River. Other structural alterations, such as the presence of the weir
in the run and the hardening of much of the shoreline, were accounted for as they affect
the hydraulic and ecological characteristics of the spring run and river system.
The term "minimum flows and levels" is often used to identify regulations that address
the hydrologic requirements of natural systems, as many biological communities
respond to changes in water levels as well as flow. However, the determination of
minimum flows and levels for Sulphur Springs only involved a flow component, as it was
concluded that water level fluctuations in the spring pool are relevant only as they affect
discharge from the spring pool. Therefore, the term "minimum flows" (without levels) is
used throughout this report
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