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

4.5.2 Fish Passage Standard
For development of minimum flows, it is desirable to maintain longitudinal
connectivity along a river corridor, to the extent that this connectivity has
historically occurred. To secure the benefits associated with connectivity and
sustained low flows, a 0.6 ft fish-passage criterion was used to develop a low
flow standard for the Alafia River corridor. The fish passage criterion was used
by the District for development of proposed minimum flows and levels for the
Upper Peace River (SWFWMD 2002) and was found to be acceptable by the
panel that reviewed the proposed flows (Gore et al. 2002).
Flows necessary for fish passage at each HEC-RAS cross-section were
identified using output from multiple runs of the HEC-RAS channel model. The
flows were determined by adding the 0.6 ft depth fish passage criterion to the
elevation of the lowest spot in the channel and determining the flow necessary to
achieve the resultant elevations. At many cross-sections, the minimum channel
elevation plus 0.6 ft resulted in a water surface elevation lower than the elevation
associated with the lowest modeled flow. These cross-sections were located in
pool or run areas, where fish passage could occur, even during periods of little or
no flow.
Ultimately, linear regressions between the stage at each cross-section and the
flow at the USGS Lithia gage were used to determine flows at the Lithia gage
that corresponded to the target fish-passage elevation at the cross sections
(Figure 4-12 as an example). The flow at the Lithia gage that was sufficient to
provide for fish passage at all HEC-RAS cross sections at all sampled crosssections
was used to define the fish passage, low flow standard for the Alafia
River corridor.
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