The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
3.3 Tidal water level fluctuations in the spring run
Water levels in Sulphur Springs Run show fluctuations in response to tides in the Lower
Hillsborough River. The river near the spring is strongly tidal, with a mean daily
amplitude in water levels of about 1.0 meters at the recorder near Nebraska Ave.
(USGS station Hillsborough River at Sulphur Springs). Stage duration curves of water
levels at this site and the recorder in the spring run are presented in Figure 3-1. The
curves are very similar above the median water level for the spring run, which is
approximately 0.7 ft. NGVD. Below that level, however, the curves diverge and greater
fractions of values in the river are below 0.0 feet, extending to a minimum value of –2.7
ft. These curves reflect that at higher tide stages water levels in the spring run closely
track water levels in the river, but at low tide stages water levels in the river fall to lower
levels than in the run.
Figure 3-1. Stage duration curves of water levels in the upper
spring run and the Hillsborough River near the mouth of the spring.
This relationship is also shown in a time series plot of water levels for the spring run and
river for one week in January 2001 (Figure 3-2). Springflow rates during this period were
at 23 to 25 cfs and not altered by withdrawals from the spring pool (normal flows). At
higher tides, water levels in the spring run and river were nearly the same, as water
levels in the river created a backwater condition that controlled water levels in the run.
On falling tides, however, water levels in the spring run stabilized around 0.25 feet while
levels in the river fell to near – 1 feet. These differences are due to the effect of the weir,
which tends to retain water in the upper spring run due to the hydraulic constriction of
the weir opening.
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