The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
requirements of a thermal refuge for manatees the lower river near the spring. An
exception to this is that minimum flows that alternate between 18 and 10 cfs or 13 and
10 cfs based on tide stage were not evaluated. Instead, a scenario that involves a
constant minimum flow of 10 cfs to the spring run was simulated, with the assumption
that if this minimum flow met the requirements of a thermal refuge, minimum flows that
used 10 cfs in combination with higher minimum flow would as well.
As described in Section 4.3, minimum flows for Sulphur Springs will most likely be in
effect when there is no flow from the Hillsborough River dam. Therefore, no discharge
from the Hillsborough Reservoir was assumed for all thermal scenarios that were
evaluated. A minimum flow of 10 cfs of spring flow diverted to the base of the dam was
included in all non-baseline scenarios to comply with the adopted minimum flow for the
Lower Hillsborough River. Comparison of this scenario with the historic baseline is used
to see if the adopted minimum flow for the lower river meets the requirements of a
thermal refuge for manatees.
Table 5-5. Flow regimes for the thermal modeling scenarios. All flows reported
in cubic feet per second (cfs).
SCENARIOS
SPRING
FLOW TO
SPRING
RUN
Spring
flow to
base of
dam
Flow from
reservoir
Removal for
water
supply
Baseline 31 0 0 0
A 18 10 0 3
B 13 10 0 8
C 10 10 0 11
These comparisons provide an estimate of temperature changes in the river near the
mouth of the spring resulting from the combinations of rerouting of springflow to the
base of the dam or removal of springflow to the reservoir. Based on communications
with the FMRI (B.Ackerman, pers. Communication), it was agreed that two scenarios
would be considered equivalent if difference between mean water temperatures for the
cell in the river adjacent to the mouth of the spring was less than less than 2° C. This
cell represents all vertical layers in a bank to bank section of the river that is 50 meters
long centered at the spring mouth. It was assumed that if the temperature change in this
cell was acceptable, that conclusion would also hold for the spring run, where the
temperature change is expected to be less.
All four model scenarios were run for each of the two separate time periods, the “coldest
period” (January-February 1977) and the “thermal refuge period” (November 29-
December 4, 2003). The mean water temperatures in the cell adjacent to the mouth of
the spring are listed for the baseline and each of the three scenarios in Table 5-6. The
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