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

flow regimes and these life history requirements can be used to develop
protective minimum flows.
To achieve this goal, Physical Habitat Simulation (PHABSIM) protocols have
been added to the District's approach for establishing minimum flows for river
systems. PHABSIM is the single most widely used methodology for establishing
"minimum flows" on rivers (Postel and Richter 2003), and its use was
recommended in the peer review of proposed MFLs for the upper Peace River
(Gore et al. 2002). The technique has, however, been criticized, because it is
based on the specific requirements of a few select species (typically fish of
economic or recreational value), and it is argued that such an approach ignores
many ecosystem components. This criticism is overcome in the current District
approach for MFLs development, since PHABSIM represents only one of several
tools used to evaluate flow requirements. Results of PHABSIM analyses are
used to assess flow needs during periods of low to medium flows.
3.3.4 Woody Habitats
Stream ecosystem theory emphasizes the role of instream habitats in
maintaining ecosystem integrity. These habitats form a mosaic of
geomorphically defined substrate patches (Brussock et al. 1985), each with
characteristic disturbance regimes and macroinvertebrate assemblages (Huryn
and Wallace 1987). For instance, invertebrate community composition and
production in a blackwater river varies greatly among different habitat types,
where the habitats are distinguished by substrates of different stability (e.g.,
sand, mud and woody debris) (Benke et al. 1984, Smock et al. 1985, Smock and
Roeding 1986). Ecosystem dynamics are influenced by the relative abundance
of these different habitat types. Changes in community composition and function
occurring along the river continuum are in part a consequence of the relative
abundance of different habitat patches, which are under the control of channel
geomorphology and flow. For determining MFLs, we identify key habitats and
features that play a significant role in the ecology of a river system using a
habitat-based approach that includes a combination of best available data,
published research, and site specific field work.
Among the various instream habitats that can be influenced by different flow
conditions, woody habitats (snags and exposed roots) are especially important.
In low-gradient streams of the southeastern U.S.A. coastal plain, wood is
recognized as important habitat (Cufney and Wallace 1980; Benke et al. 1984,
Wallace and Benke 1984; Thorp et al. 1990; Benke and Wallace 1990). Wood
habitats harbor the most biologically diverse instream fauna and are the most
productive habitat on a per unit area basis (Benke et al. 1985). Comparisons of
different instream habitats in a southeastern stream indicates that production on
snags is at least twice as high as that found in any other habitat (Smock et al.
1985).
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