Chapter 1 Minimum Flows and Levels - Southwest Florida Water ...

and the habitats and ecological indicators associated with the goals are
addressed in subsequent sections of this chapter. Field and analytical methods
used to assess hydrologic requirements associated with the habitats and
indicators are presented in Chapter 4, and results of the minimum flows and
levels analyses are presented in Chapter 5.
3.3.1 Fish Passage and Recreational Use
Ensuring sufficient flows for the passage or movement of fishes is an important
component of the development of minimum flows. Maintenance of these flows is
expected to ensure continuous flow within the channel or river segment, allow for
recreational navigation (e.g., canoeing), improve aesthetics, and avoid or lessen
potential negative effects associated with pool isolation (e.g., high water
temperatures, low dissolved oxygen concentrations, localized phytoplankton
blooms, and increased predatory pressure resulting from loss of habitat/cover).
Tharme and King (1998, as cited by Postel and Richter 2003), in developing a
"building block" approach for South African rivers, listed the retention of a river's
natural perenniality or nonperenniality as one of eight general principles for
managing river flows. For many rivers within the District, flows and
corresponding water depths adequate for fish passage are currently or were
historically maintained by baseflow during the dry season (Figure 3-1). For
example, in the upper Peace River, historical flows were sufficient for maintaining
a naturally perennial system and flow was sufficiently high during the low-flow
season to permit passage of fish along most of the river segment (SWFWMD
2002). Recent flows in the upper Peace River have not, however, been sufficient
for fish passage much of the time. Historic flows in other District rivers, such as
the Myakka River were probably intermittent, historically, but have increased in
recent years. Evaluation of flows sufficient for fish in support of minimum flows
development may, therefore, involve consideration of historic or recent flow
conditions with respect to perenniality and the likelihood of fish passage being
maintained naturally (i.e., in the absence of consumptive water use).
3.3.2 Wetted Perimeter Inflection Point
A useful technique for evaluating the relation between the quantity of stream
habitat and the rate of streamflow involves an evaluation of the "wetted
perimeter" of the stream bottom. Wetted perimeter is defined as the distance
along the stream bed and banks at a cross section where there is contact with
water. According to Annear and Conder (1984), wetted perimeter methods for
evaluating streamflow requirements assume that there is a direct relationship
between wetted perimeter and fish habitat. Studies on streams in the southeast
have demonstrated that the greatest amount of macroinvertebrate biomass per
unit reach of stream occurs on the stream bottom (e.g., Benke et al. 1985).
Although production on a unit area basis may be greater on snag and root
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