The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
The results of the vertical profile data for experiment 5 were supported by the results of
the continuous recorder, which showed a peak salinity value of 12.6 ppt on the sampling
day (Appendix H). There was considerable covariation of salinity with tide stage at the
continuous recorder, however, as the incursion occurred primarily at higher tide stages.
Daily salinity range values from the continuous recorder show that salinity incursions
also occurred during the five days prior to June 12 th , which also had flows of 13 cfs
(Appendix I). However, no incursions were noted between June 3 rd and 6 th , when flows
were at the same rate. Tide stage values in the Hillsborough River also listed in
Appendix I show that salinity incursions during this controlled release typically occurred
on days when maximum tide stages were over 2.0 feet. Particularly strong incursions
occurred on June 10 th and 12 th , when tide stages in the river peaked at 2.4 feet and 2.7
feet, respectively.
In summary, the six experimental flow tests provide a limited data base for evaluating
the effects of flow reductions on salinity in the spring run. These data indicate the
response of salinity in the run can vary greatly within a narrow range of flows, or even
for the same rate of flow. Salinity incursions did not occur on three dates with moderate
flows (16 to 23 cfs), while another experiment at 19 cfs found a slight incursion that
went only a short distance above the weir. However, only one experiment was
conducted with a prolonged controlled release. The combined data from the vertical
profiles and the continuous recorder during that release show that salinity incursions
can vary greatly from day to day at a constant flow rate of 13 cfs. As will be discussed
further, a principal factor affecting this variability is tide stage in the lower Hillsborough
River.
5.2.4 Salinity response at the continuous recorder in the upper spring run to
variable flows
The continuous recorder data that were collected in the spring pool, the spring run, and
the nearby reaches of the Hillsborough River provide valuable data for evaluating the
relationships of spring flow and tide stage with salinity incursions in the spring run. The
recorder data for the upper spring run evaluated in this report extend from May 25, 1999
to December 31, 2002. During this period, there were 836 days when flows in Sulphur
springs ranged from 0 cfs to the average flow rate of 31 cfs.
The number of days that flow rates from the spring occurred in 1 cfs intervals are plotted
in Figure 5-4. The data are limited to periods when there was no flow from the
Hillsborough River Dam, as this is when meaningful data can be collected regarding
salinity incursions into the spring run. During the period of study, there were 107 days
that flows were 1 cfs from the spring pool. There were also a large number of days at 2
and 3 cfs. Although these data are informative for examining the response of the spring
at very low flows, they are likely below a minimum flow to be established for the spring.
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