The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
For the evaluation of minimum flows, it is important to view the effects of withdrawals
from Sulphur Springs on a short-term basis. To illustrate patterns of daily withdrawals
from the spring during very dry periods, average daily pumpage values are plotted for
1999 - 2002 in Figure 2-11. The flat shape of the top of the pumpage hydrograph
reflects series of consecutive days when the withdrawals were taken continuously at the
pump capacity of 20 mgd (31 cfs). The most prolonged period of pumping from the
spring occurred during May though July 2000, with frequent but less consistent pumping
occurring during the first part of 2001.
When they have occurred, withdrawals by the City of Tampa have had a major effect on
flows from the spring pool to the spring run. The capacity of the pump (20 mgd) is
almost as great as the average flow of Sulphur Springs (22 mgd or 34 cfs), and until
recently, pumpage by the City of Tampa often caused flow to the spring run to fall to
zero or very low rates of flow. Average daily flows from spring to the run are shown for
the 1999-2002 period in Figure 2-12. Comparison to Figure 2-11 shows that when
withdrawals were in effect, discharges from the pool fell to very low values. When
withdrawals ceased, there was a rapid increase in discharge from the spring pool.
The period of high flow (> 50 cfs) that occurred primarily in 1999 was due to opening of
the gate at the spring outlet. During this period, the City opened the structure to lower
water levels in the pool so that work on the swimming pool in the Sulphur Springs Park
could be undertaken without damaging the structure of the swimming pool. Raising the
gate and lowering water levels in the spring pool induces greater ground-water
discharge due to less head pressure over the spring vent. In the spring of 1999, the City
closed the structure and began withdrawals for water supply, as shown by the drop in
flows seen in April though June of that year (Figure 2-12). Additional information on the
ground-water relations and flow characteristics of Sulphur Springs are presented in later
sections of this report.
2.3.1 Recent improvements to the diversion facilities at Sulphur Springs
Modifications were made to the water diversion facilities associated with Sulphur
Springs during 2001 to allow for better management of flows from the spring pool. As
part of the minimum flow rule for the Lower Hillsborough River that was adopted in the
year 2000, it was established that diversions from Sulphur Springs could be used to
provide the 10 cfs minimum flow at the base of the Hillsborough River dam. To
accomplish this objective, a junction was put in the pipe that leads from Sulphur Springs
to the reservoir so that spring waters can be released to the lower river near the base of
the dam. A valve and flow meter were installed at this junction so that varying amounts
of spring water could be diverted either into the reservoir or to the base of the dam. A
100 ft. long flume was constructed that extends from this junction to the river below the
dam (Figure 2-13). The turbulence created by this flume aerates the spring water before
it is released to the lower river.
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