Alafia River Minimum Flows and Levels - Southwest Florida Water ...

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), any minimum flows methodology should involve
more than a consideration of immediate fish needs or the absolute minimum needed
to sustain a particular species or population of animals, but 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 (2004), 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 seasons 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
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