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

then used to estimate percent of flow reductions for Block 3 that would result in
no more than a 15% reduction in the number of days of floodplain inundation.
The analysis suggested that a stepped approach to water allocation during Block
3 would meet the established criteria.
The peer review panel feels that consideration of high flows and patterns of
floodplain inundation is commendable. The use of a 15% reduction in the number
of days of inundation is an appropriate criterion for water allocation and is
consistent with the working definition of significant harm used throughout the
report.
Inclusion of information on the methods used for identifying and characterizing
floodplain plant communities and soils in the Alafia and Myakka reports is helpful
and represents a significant improvement in the readability of these reports and
interpretation of results. We commend District staff for incorporating these and
other changes, which were recommended in previous peer reviews, in these
reports.
SNAG AND ROOT INUNDATION
Woody substrates (snags and exposed roots) are a critical habitat in most low
gradient southeastern streams. Woody substrates are often the most productive
habitat (on a unit area basis). Wood also provides shelter for freshwater fishes
and basking sites for aquatic herpetofauna. Submerged wood also is important in
biogeochemical transformation because biofilms develop on submerged wood,
carbon and nutrient processing are enhanced and overall stream metabolism is
increased.
The District estimated the mean elevation of woody substrates using instream
habitat cross-sections in the Alafia and Myakka rivers. Then, an estimate of the
average frequency of inundation was determined using the two benchmark
periods. Data from the most recent period (1970-1999) were used because it was
more conservative (i.e., it was during a period of lower stream flow). This was
compared with previously prescribed flow reductions in Blocks 1 and 3 to
determine the overall effect on woody substrate inundation. These analyses were
used to help determine the allowable flow allocation during Block 2 and then
estimate flow allocations that would result in no more than a 15% reduction in
days of inundation over the entire year.
The peer review panel agrees with the District that woody substrates are a critical
habitat in the Alafia and Myakka rivers and that their duration of inundation
should be considered in flow allocation strategies. The approach adopted by the
District is reasonable and consistent with other recommendations made in the
report.
Appendix A XIV