The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
occurring. The data discussed above indicates that flows of greater than 18 cfs prevent
the incursion of river water above the weir, except for very high tide stages.
The relationship of tide stage (water level) in the river to salinity values in the spring run
is illustrated in Figure 5-8, in which 15-minute salinity values at the recorder in the upper
run are plotted against simultaneous water level values in the river for days when flows
from the spring were in the range of 10 to 18 cfs. Although there is considerable scatter
in this plot, there a general positive relationship between salinity in the run and tide
stage in the river. With the exception of one data point, salinity values above 3 ppt did
not occur when water levels in the river were below –0.5 feet NGVD. The occurrence of
high salinity values increases when water levels in the river rise between 0 and 1 foot
NGVD, as this is when river levels exceed the elevation of the bottom of the opening in
the weir. Higher water levels continue to push more brackish water into the run, as
salinity values above 10 ppt were only recorded when water levels exceeded about 1
foot NGVD.
20
Sulphur Springs Salinity (ppt)
15
10
5
0
-3 -2 -1 0 1 2 3
Hillsborough Water Level (ft, NGVD)
Figure 5-8. Relation between 15-minute values for water levels in
the lower river and salinity at the recorder in the upper spring run for
flows between 10 and 18 cfs from the spring pool.
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