MANASOTA & PEACE RIVER BBDs Meeting Notebook 10-21-09.docx

B273
MFL Stream Diversion and Assessment Project
Project Type Basin Initiatives
AOR(s)
Water Supply, Natural Systems
Basin(s) Alafia River, Hillsborough River, Northwest Hillsborough, Coastal Rivers, Pinellas-Anclote River,
Withlacoochee River, Peace River, Manasota
Cooperator(s)
Project Manager MORALES, JON
Task Manager(s)
Status Ongoing
Description
To further validate existing stream Minimum Flows and Levels (MFL) methodology consistent with peer review
recommendation. A frequent focus of criticism of the MFL methodology applied by the District to rivers and estuaries
is the use of a 15 percent habitat loss criterion as a threshold for assessing "significant harm." Quoting from the peer
review of the Braden River MFL, the panel noted:
" The draft report describes the metrics used to define the limit at which further withdrawals would be significantly
harmful to the water resources or ecology of the area as stated in Florida statutes. The authors note that significant
harm was not defined in statute. The District chose to interpret significant harm as the loss of flows associated with
fish passage and maximization of stream bottom habitat with the least amount of flow and quantifiable reductions in
habitat. Overall, this is a reasonable approach from an ecological perspective and likely satisfies the intent of the
statute. The authors state that, [in] general, instream flow analysts consider a loss of more than 15% habitat, as
compared to undisturbed or current conditions, to be a significant impact on that population or assemblage. The
authors further note, in our opinion, correctly, that there are few `bright lines which can be relied upon to judge when
`significant harm occurs. Rather loss of habitat in many cases occurs incrementally as flow decline, often without a
clear inflection point or threshold. Nevertheless, the 15% habitat loss criterion remains one of the least rigorous, most
subjective aspects of the District's approach to setting MFLs. Justification for this threshold is based on common
professional practice in interpreting the results of PHABSIM analyses (Gore at al. 2002), a review of relevant literature
where reported percentage changes ranged from 10 to 33%, and on previous peer reviews that found the 15%
threshold to be reasonable and prudent, especially given the absence of clear guidance in the statute or in the
scientific literature on levels of change that would constitute significant harm (e.g., Shaw et al. 2005). 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. . . . .
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. "
This project represents the best means for validating the effect that a given flow reduction has on available habitat and
the biota of a stream segment. District staff proposes to locate an acceptable stream segment in order to conduct
controlled diversions from a defined stream segment in order to evaluate the impact that a range of flow and habitat
reductions has on the biota (e.g., fishes, macroinvertebrates) and water resource values. It is envisioned that such a
project will require a number of years to complete (possibly a decade), and an annual commitment of significant
resources to accomplish.
Benefits
If implemented, this project will provide as definitive a test of the 15 percent habitat loss criterion as is practical under
field conditions, and the results will be widely applicable to stream assessments and the development of environmental
flows though out the country.
Costs
Funding in FY2009 is currently for $150,000. The combined Basin Board's contribution is 50% or $75,000 or $9,375
from each of the eight basin boards, with the remaining 50% ($75,000) to be funded by the Governing Board. A small
amount has been budgeted for parts and supplies and travel. Total requested funding for FY2010 is $150,000.00.
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