The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
Formation and act as a hydrologic confinement layer separating the surficial water table
from the underlying Upper Floridan aquifer.
Beneath the confining layer is the weathered surface of the Miocene Tampa Limestone,
underlain by the Oligocene Suwannee Limestone, Eocene Ocala Limestone, Avon Park
Limestone and the Oldsmar Limestone. Together these carbonate sequences comprise
the Upper Floridan aquifer. The Tampa Limestone is a white, gray, and tan sandy
limestone with a great number of fractures, solution channels and numerous sinkholes.
It is also an important source of water supply. The underlying Suwannee Limestone is a
yellow-white to light brown fossiliferous limestone and is the source of most domestic
water in the area (Knutilla and Corral, Jr. 1984).
Although the Avon Park Limestone is an important source of water, particularly from the
highly fractured zone, it is separated from the overlying formations by the Ocala
Limestone, a yellow-gray, chalky, fossiliferous limestone that is not a very good
producer of water. The Ocala acts as a semi-permeable confining unit separating the
Avon Park from the overlying units. The consequence is that the portions of the aquifer
below the Suwannee Limestone are not likely to be important contributors to the flow at
Sulphur Spring.
2.4.2 Springflow characteristics
Sulphur Springs is an artesian spring from which ground waters discharge due to
hydrostatic pressure in the underlying aquifers. The average flow for Sulphur Springs is
31.4 cfs for the period 1991 through 2002. Correcting this value for withdrawals by the
City of Tampa (adding withdrawals to flow) yields an average flow of 34.3 cfs. Flows
from Sulphur Springs exhibit slight seasonal variation in response to the progression of
dry and wet seasons in west-central Florida. Average monthly withdrawal-corrected
flows range from 28.9 cfs in June, just after the spring dry season, to 39.4 cfs in
September (Figure 2-15). Duration curves for flows at Sulphur Springs are presented in
Figure 2-16 for days when there were no withdrawals and the complete daily record
(including withdrawals). The curves are relatively similar but diverge at low flows,
showing the effect of the periodic withdrawals by the City. As with most other springs,
flows from Sulphur Springs are much more stable than flows in freshwater streams that
receive surface runoff. Eighty percent of the daily flow values with no withdrawals range
between 26 and 48 cfs (Figure 2-16).
Water flowing from the spring has two sources. The primary source is from the Tampa
and Suwannee limestones of the Upper Floridan Aquifer. Much, if not all, of the ground
water component flows along fractures and solution channels. Some of the solution
channels connect with sinkholes in the area, which are extremely numerous (Figure 2-
17). To a lesser degree some stormwater runoff, which has been captured by the sinks,
flows along the same conduits to Sulphur Springs, although that contribution has
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