Weeki Wachee River System Recommended Minimum Flows and ...

1) flood flows that determine the boundaries of and shape floodplain and valley
features;
2) overbank flows that maintain riparian habitats;
3) in-channel flows that keep immediate streambanks and channels functioning;
and
4) in-stream flows that meet critical fish requirements.
As emphasized by Hill et al. (1991), minimum flows methodologies should involve more
than a consideration of immediate fish needs or the absolute minimum required to
sustain a particular species or population of animals, and should take into consideration
“how streamflows affect channels, transport sediments, and influence vegetation.”
Although, not always appreciated, it should also be noted “that the full range of natural
intra- and inter-annual variation of hydrologic regimes is necessary to [fully] sustain the
native biodiversity” (Richter et al. 1996). Successful completion of the life-cycle of many
aquatic species is dependant upon a range of flows, and alterations to the flow regime
may negatively impact these organisms as a result of changes in physical, chemical and
biological factors associated with particular flow conditions.
Recently, South African researchers, as cited by Postel and Richter (2003), listed eight
general principles for managing river flows:
1) "A modified flow regime should mimic the natural one, so that the natural
timing of different kinds of flows is preserved.
2) A river's natural perenniality or nonperenniality should be retained.
3) Most water should be harvested from a river during wet months; little should
be taken during the dry months.
4) The seasonal pattern of higher baseflows in wet season should be retained.
5) Floods should be present during the natural wet season.
6) The duration of floods could be shortened, but within limits.
7) It is better to retain certain floods at full magnitude and to eliminate others
entirely than to preserve all or most floods at diminished levels.
8) The first flood (or one of the first) of the wet season should be fully retained."
Common to this list and the flow requirements identified by Hill et al (1991) is the
recognition that in-stream flows and out of bank flows are important and that seasonal
variability of flows should be maintained. Based on these concepts, the preconception
that minimum flows (and levels) are a single value or the absolute minimum required to
maintain ecologic health in most systems has been abandoned in recognition of the
important ecologic and hydrologic functions of streams and rivers that are maintained by
different ranges of flow. And while the term “minimum flows” is still used, the concept
has evolved to one that recognizes the need to maintain a “minimum flow regime”. In
Florida, for example, the St. Johns River Water Management District (typically develops
multiple flows requirements when establishing minimum flows and levels (Chapter 40-
C8, F.A.C) and for the Wekiva River noted that, “[s]etting multiple minimum levels and
flows, rather than a single minimum level and flow, recognizes that lotic [running water]
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Proposed Minimum Flows and Levels for Weeki Wachee River
Purpose and Background Page 3 of 164