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

The draft upper Braden report continues the District’s practice of using a 15%
change in habitat availability as the threshold for defining significant harm and
now applies this threshold broadly to include both spatial and temporal loss of
habitat or connectivity.
The Panel again acknowledges that the use of this criterion is rational and
pragmatic, but also recognizes that the specific value of 15% is subjective and
has only modest validation or support from the primary literature. Arguments can
and likely will be made for both lower and higher percentages of habitat loss to
be used for defining significant ecological harm. Other work has been done, in
addition to the literature that is already cited, and the Panel believes it would be
prudent to expand the literature review to gather as much additional supporting
documentation as possible, much of which will be gray literature. Where lower or
higher percentages have been used elsewhere, it would be illuminating to
understand the rationale for these decisions (e.g., lower percentages used where
imperiled or more sensitive species are concerned, higher percentages for more
degraded systems, etc.).
What happens if you use a 5% or a 33% reduction in habitat in your analyses?
How would these values affect the recommendations for MFLs for an ecosystem
like the upper Braden River? The Panel is not advocating doing the analyses on
all rivers with multiple values for acceptable habitat loss, but it would be
informative to do such a sensitivity analysis for a less difficult river like the upper
Braden River. Such an analysis of the sensitivity of the MFLs to setting different
thresholds of habitat loss where significant harm occurs would assist in the
discussion of why a specific value (e.g., 15%) has been chosen.
More importantly, however, is the need for the District to commit the resources
necessary to validate the presumption, that a 15% decrease in spatial or
temporal habitat availability or a 15% increase in violations of the low-flow
threshold, does not cause significant harm. The District would appear to be in an
excellent position to implement monitoring, natural experiments, and other
analyses necessary to evaluate the effectiveness of this threshold and establish
a framework for adaptive management. Several riverine MFLs
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