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

a 15% change in habitat availability as a measure of unacceptable loss, it is
important to note that percentage changes employed for other instream flow
determinations have ranged from 10% to 33%. For example, Dunbar et al.
(1998) in reference to the use of PHABSIM noted, "an alternative approach is to
select the flow giving 80% habitat exceedance percentile," which is equivalent to
a 20% decrease. Jowett (1993) used a guideline of one-third loss (i.e., retention
of two-thirds) of existing habitat at naturally occurring low flows, but
acknowledged that, "[n]o methodology exists for the selection of a percentage
loss of "natural" habitat which would be considered acceptable." The state of
Texas utilized a target decrease of less then 20% of the historic average in
establishing a MFL for Matagorda Bay ( http://www.tpwd.state.tx.us/texaswater/
coastal/freashwater/matagorda/matagorda.phtml).
3.2 Resources and Area of Concern
The resources addressed by the District's minimum flows and levels analyses
include the surface waters and biological communities associated with the river
system, including the river channel and its floodplain. A river system is
physiographically complex, with a meandering channel and associated floodplain
wetlands. This hydrologic and physical setting provides habitat for a diverse
array of plant and animal populations. Because "[a]quatic species have evolved
life history strategies primarily in direct response to the natural flow regimes"
(Bunn and Arthington 2002), a primary objective of minimum flows and levels
analysis is to provide for the hydrologic requirements of biological communities
associated with the river system. Human uses of the natural resources are also
an important consideration for the establishment of minimum flows and levels.
Such uses include fishing, swimming, wildlife observation, aesthetic enjoyment,
and boating.
3.3 Resource Management Goals and Key Habitat Indicators
The SWFWMD approach for setting minimum flows and levels is habitat-based.
Because river systems include a great variety of aquatic and wetland habitats
that support a diversity of biological communities, it is necessary to identify key
habitats for consideration, and, when possible, determine the hydrologic
requirements for the specific biotic assemblages associated with the habitats. It
is assumed that addressing these management goals will also provide for other
ecological functions of the river system that are more difficult to quantify, such as
organic matter transport and the maintenance of river channel geomorphology.
Resource management goals for the Alafia River addressed by our minimum
flows analysis include:
3-2