The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
The sum of these considerations in that the establishment of minimum flows for Sulphur
Springs is a management issue that primarily applies when there is no flow to the lower
river from the Hillsborough River reservoir and minimum flows for the lower river are in
effect. As a result, the District's minimum flows analysis for Sulphur Springs focused on
conditions that occur in the spring run and river during periods of no flow from the
Hillsborough River reservoir. It was concluded that these no-flow conditions represent
times when the spring run and lower river are most susceptible to impacts that can
result from reductions in springflow. Minimum flows adopted for such conditions will
protect these resources during high flow conditions at the dam as well.
4.4 Selection of management goals and ecological indicators for evaluating the
effects of reduced flows
An important component of a minimum flow evaluation is determining what ecological
characteristics of the resource are to be protected from impacts that can result from
withdrawals and reduced flows. This approach can be expressed as a series of
resource management goals. Each goal can in turn include a group of ecological
indicators, or characteristics of the resource for which hydrologic requirements can be
identified and the effect of reduced flows evaluated. The selection of ecological
indicators is an important step in a minimum flows determination, as it affects the overall
evaluation of potential impacts to the ecosystem as flows are reduced due to
withdrawals.
The nature of ecological indicators can vary. For example, the hydrologic requirements
of a single species, such as a highly prized gamefish, can be quantified and utilized as a
valuable indicator. Alternately, the hydrologic requirements of group of species with
similar life histories can be used, such as the durations and depths of inundation
suitable for wading birds. One approach is to identify the suitable habitat for a group of
species and quantify changes in the amount of suitable habitat as a function of water
levels or flow. In many cases, relationships between the amount of suitable habitat and
flow can be quantified much better than the direct response of a species to a change in
flow. By providing suitable habitats, it can be reasonably assumed that the hydrologic
requirements of the species using those habitats will be met. The identification of
habitats can vary, ranging from inundation of woody snags in a freshwater stream to
areas within suitable salinity ranges in estuarine ecosystems.
On many water bodies it is desirable to employ a variety of ecological indicators to
account for different components of the ecosystem. These indicators should be
ecologically important, in that they account for major components or processes in the
ecosystem in question. Collectively, they should be as comprehensive as possible and
address the hydrologic requirements of several key resources. Since some components
of the ecosystem may be more susceptible to flow reductions than others, it is important
that sensitive indicators be selected if they are important to ecosystem processes.
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