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

5.5.1 Application of PHABSIM for Block 2
PHABSIM analyses were used to model potential changes in habitat availability
for several fish species and macroinvertebrate diversity during Block 2, which
runs from October 28 through April 19. Results were evaluated for two locations
in the Alafia River near SWFWMD cross-section locations 27 and 64. The
reductions in historic flow greater than about 34% resulted in more than a 15%
loss of available habitat for largemouth bass adults (Figure 5-9). This percent-offlow
reduction was considered for use in the development of a prescribed flow
reduction for Block 2 at the Lithia gage site.
Predicted Habitat Gain/Loss for Laregemouth Bass Adults Based on Historic Flow Conditions (1970-1999)
being reduced by 10, 20, 30, and 40 percent at Alafia River Site 64
10%
5%
February
March
0%
January
December
Habitat Gain/Loss
-5%
-10%
-15%
November
10% Flow Reduction
20% Flow Reduction
30% Flow Reduction
40% Flow Reduction
-20%
October
-25%
Figure 5-9. Predicted habitat gain/loss for adult large mouthbass based on the flow record
from 1970 to 1999 and flow reductions of 10, 20, 30, and 40 percent.
5.5.2 Instream Habitats
Bottom habitats, including sand, mud and bedrock, were dominant, based on the
linear extent of the habitat along the cross-sections (Figure 5-10). Wetland tree
habitat was also abundant. Exposed roots, snags and wetland plants comprised
substantially less of the linear habitat. Relative elevations of the habitats were
consistent among the cross-sections (Figure 5-11). Wetland trees were typically
situated near the top of the banks with wetland plants and exposed roots
occurring at slightly lower elevations. Snags were found in association with the
bottom habitats. The occurrence of exposed roots at relatively high elevations is
important because inundation of this habitat results in inundation of habitats
located at lower elevations.
5-13