The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
The number of days of record range from 6 to 26 for flows between 4 and 21 cfs. There
is a peak in the number of days for flows between 25 to 30 cfs, which corresponds to
commonly occurring normal flows for the spring. The number of 15-minute observations
of salinity for each flow class are also plotted in Figure 5-4.
0 5 10 15 20 25 30
120
Flows@Days.grf
12000
Total Days
80
40
10000
8000
6000
4000
2000
Total Number of 15 Minute Observations
0
0 5 10 15 20 25 30
Flow (cfs)
0
Figure 5-4. Number of days in 1 cfs flow classes for flows
from Sulphur Springs pool. Data restricted to periods when
there was no flow to the lower river from the Hillsborough
River reservoir.
Percentile distributions of 15-minute salinity values at the spring run recorder in 1 cfs
intervals up to 33 cfs are also shown in box and whisker plots in Figure 5-5. Thirty-three
cfs was chosen as the upper limit for the plot as the number of observations are very
limited above that amount. The median salinity value for each flow interval is shown as
the lateral line across the interior of each box, while the top and bottom of the box
represent the 25 th and 75 th percentile values respectively. The upper whisker extends
between the 75 th percentile to the 95 th percentile, and the upper set of dots represent
individual 15-minute data points that occur above the 95 th percentile.
The data presented in Figure 5-5 and following figures were limited to periods when
there was no flow from the Hillsborough River reservoir, as flow from the dam can result
in fresh water in the river near the spring mouth and mask the effect of any incursions
into the spring run. Also, as discussed in Chapter 4, the establishment of minimum flows
for Sulphur Springs primarily applies to periods of no discharge from the dam. Values of
less than 3 cfs were used to identify no-flow days, as the USGS sometimes reports
values of 2 to 3 cfs to represent leakage through the dam.
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