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

Peace River at Zolfo Springs, FL. streamflow gage site), the District used a
"reference" period, from 1940 through 1956, to evaluate flow regime changes
(SWFWMD 2002). More recently, the District has adopted an approach for
establishing benchmark flow periods that involves consideration of the effects of
multidecadal climatic oscillations on river flow patterns (Kelly 2004; Shaw et al.
2004). The approach, which led to identification of separate benchmark periods for
flow records collected prior to and after 1970, has been utilized for analyses of flows
in the Alafia River.
Following assessment of historic and current flow regimes, and the factors that have
affected their development, the District develops protection standard statistics or
criteria for preventing significant harm to the water resource. For the upper Peace
River, criteria associated with the fish passage in the river channel and maximization
of the wetted perimeter were used to recommend a minimum low flow (SWFWMD
2002). Criteria associated with medium and higher flows that result in the inundation
of woody habitats associated with the river channel and vegetative communities on
the floodplain were described. These criteria were not, however, used to develop
recommended levels, due to an inability to separate water withdrawal impacts on
river flow from those associated with structural alterations within the watershed. For
the Alafia River, the District has applied approaches associated with development of
medium to high flow criteria per recommendations in the peer review of the
proposed upper Peace River minimum flows (Gore et al. 2002). These efforts have
included collection and analyses of in-stream fish and macroinvertebrate habitat
data using the Physical Habitat Simulation (PHABSIM) system, and evaluation of
inundation characteristics of floodplain habitats.
1.5.2 A Building Block Approach
The peer-review report on proposed MFLs for the Upper Peace River (Gore et al.
2002) identified a "building block" approach as "a way to more closely mirror original
hydrologic and hydroperiodic conditions in the basin". A building block approach to
the development of regulatory flow requirements typically involves description of the
natural flow regime, identification of building blocks associated with flow needs for
ecosystem specific functions, biological assemblages or populations, and assembly
of the blocks to form a flow prescription (Postel and Richter (2003). As noted by the
panelists comprising the Upper Peace River MFL review panel, "assumptions behind
building block techniques are based upon simple ecological theory; that organisms
and communities occupying that river have evolved and adapted their life cycles to
flow conditions over a long period of pre-development history (Stanford et al. 1996).
Thus with limited biological knowledge of flow requirements, the best alternative is to
recreate the hydrographic conditions under which communities have existed prior to
disturbance of the flow regime." Although in most cases, the District does not
expect to recreate pre-disturbance hydrographic conditions through MFL
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