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

Conversely, since most of the United States including the panhandle of Florida,
has actually seen higher rainfall over the last thirty years (refer to Enfield et al.
2001 and McCabe and Wolock 2002), anthropogenic impacts leading to flow
reductions could go unnoticed or at least underestimated if the multidecadal
climate oscillation is not considered. This, in turn, could lead to the setting of
MFLs or their equivalent at excessively high levels. Under this scenario, the
return to a lower rainfall oscillation could cause MFLs to be violated naturally,
even in the absence of water withdrawals. In many cases, where the flow record
for a river does not span move than a few decades and includes a presumed
period of pre-impact flow data, potential problems with natural streamflow
variation may not even be noticed.
Peninsular Florida in comparison to most of the United States is almost singularly
unique when it comes to evaluating declining flow trends. The combination of a
multidecadal climate related flow decline and the requirement to develop MFLs
with the need to establish a benchmark period necessitated a full evaluation of
this relationship (refer to Kelly 2004). With the exception of the work of Enfield et
al. (2001) supported by the South Florida Water Management District, we are
aware of no other minimum flow related study that acknowledges multidecadal
differences in rainfall and flow and seeks to factor these differences into water
management decisions or minimum flows determinations.
It would probably be difficult to argue that rivers with human caused flow
reductions of 30 to 40% could tolerate even greater anthropogenic reductions
without causing significant harm. For example, considerable attention has been
focused on the Peace River at Arcadia and development of MFLs. There is a
documented decline in flows of at least 30% over the last 30 years when
compared with the preceding 30 years (e.g., Hammett 1990, SDI 2003). Some
have attributed this flow decline largely to anthropogenic factors with the
resultant expectation that no further human caused flow declines could be
tolerated without significant affects on the river system and the downstream
estuary. However, if it can be demonstrated that the observed flow declines are
largely climate related, different expectations are warranted. MFLs legislation
implicitly assumes that some anthropogenic flow reduction (e.g., withdrawals)
can occur before significant harm occurs.
Recent work related to the AMO and Florida river flow patterns suggest that at
least two benchmark periods exist in the absence of human influences. One
benchmark period would be related to a multidecadal period coincident with the
Atlantic sea surface warming (increased rainfall in peninsular Florida) and one
related to a multidecadal period of Atlantic sea surface cooling (decreased
rainfall in peninsular Florida). When developing MFLs for the upper Peace River
(see SWFWMD 2002), it was noted that there was a substantial change in the
number of days that a given flow was exceeded prior to and after 1970; similar
differences were noted for other water bodies (e.g., Alafia River, middle Peace
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