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

With respect to the two attachments: EPCHC – Mr. Ed Sherwood and Florida Coastal
Sanctuaries Program – Dr. Ann Hodgson appended to your letter, some response is
warranted.
Since the letter by Mr. Sherwood (EPCHC) posed specific questions and comments, it
is appropriate to respond to these in the order presented.
The approach to minimum flows and levels taken by the District on freshwater stream
segments in particular relies heavily on the development of benchmark periods and is
discussed in the MFL document. As EPCHC noted "the proposed multi-decadal
relationship between the AMO, rainfall, and river flow are not analyzed in detail in the
report itself. Instead, the reader is referred to a group of other documents (e.g., Enfield
et al. 2001, Basso and Schultz 2003, Kelly 2004) for a more detailed explanation." It
should be noted that the analysis performed by Kelly (2004) was based on the other two
works cited (Enfield et al. 2001 and Basso and Schultz 2003), and was designed to deal
specifically with the idea that two climatically distinct benchmark periods may exist due
to mutidecadal differences in rainfall. These reports looked at rainfall patterns and
concluded that the AMO had a significant affect on rainfall throughout the District
(Basso and Schultz 2003) and over a much broader geographic area (Enfield et al.
2001). The District realized that climatic patterns are not limited by watershed
boundaries and that the assessment of climatic affects on rainfall and river flows must
be developed with a broader perspective, and would of necessity involve analysis of
river flow patterns (trends) for many rivers within and outside District boundaries. The
argument developed by Kelly (2004) could not be developed by examining the
hydrology of a single system (e.g., Alafia River), and rather than repeat this argument in
detail in every MFL document, and due to the critical nature of the argument, the District
developed a separate report (Florida River Flow Patterns and the AMO; Kelly 2004) and
submitted if for independent scientific peer review (Shaw et al. 2004). More than a quick
examination of the relevant literature is needed to fully appreciate the importance of the
AMO in affecting rainfall and ultimately river flow patterns.
In reviewing the cited documents, EPCHC explicitly asked, "If other researchers wish to
analyze multi-decadal variations in rainfall and river flow patterns in west-central Florida,
which time periods should they designate as 'warmer Atlantic SST/higher rainfall' and
which should they designate as 'cooler Atlantic SST/lower rainfall'?" It is correctly noted
that the choice of starting and ending dates of these analyses may affect the
conclusions that are drawn from them. While it would be helpful if a consistent set of
starting and ending dates could be agreed upon, a considerable volume of work is now
being done on the AMO by many researchers, and it is likely that the selection of
beginning and ending dates will continue to vary somewhat. The beginning and ending
dates are generally selected based on visual inspection of a graphic similar to that
presented in Kelly (2004; Fig. 11). Kelly (2004) selected his starting and ending dates
with additional criteria in mind. Since comparisons were being made with river flow data
and because river flow data are not as extensive temporally as rainfall data, Kelly chose
1940 as a starting date simply because this allowed a reasonable number of river gage
Appendix D iv