The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
Problems with high coliform bacteria counts caused the City to close Sulphur Springs to
swimming and bathing in the 1980s. Remediation of this problem was determined to be
infeasible, and in the 1999 a swimming pool was constructed within the Sulphur Springs
Park for public use. Since the 1960s, the City of Tampa has periodically made withdrawals
from the spring pool to augment water supplies in the Hillsborough River Reservoir during
times of water shortages. Over the years, modifications were made to the facilities and
water control structures at Sulphur Springs to support its dual use for recreation and water
supply. The determination of minimum flows for Sulphur Springs is based on the current
configurations of the spring pool and run, which are described below.
2.2 Current physical setting of the spring pool and run
The spring is enclosed by a circular concrete wall, which creates a pool approximately 40
feet (ft.) in diameter (Figure 2-3). When the pool is full under normal flow conditions (no
withdrawals), water surface elevations in the spring pool generally fluctuate about 7.1 ft
above the National Geodetic Vertical Datum 1929 (NGVD). Water depths in the spring pool
range from about 5 to 22 ft at normal operating levels, as elevations of the bottom of the
pool range from about +2 to –15 ft. NGVD. Ground water discharges to the spring pool via
a single vent that is located near the center of the pool
Water discharges from the pool to the spring run through an operable water control
structure (Figure 2-4). When this structure is closed, water flows over the top of this
structure or flows through two flumes that are located on either side of an operable lift
gate. When the gate is opened, water discharges through the bottom of the gate to the
spring run. When the structure is closed, water levels in the spring pool are unaffected by
tides. When the structure is fully opened, water levels in the spring pool may be affected
by tidal water level fluctuations in the Lower Hillsborough River.
The spring run extends from the water control structure about 500 ft. to the mouth of the
run at the Lower Hillsborough River (Figure 2-5). The width of the run varies from about 50
to 100 ft., with the widest portions occurring in the upper half of the run near the spring
pool. Two footbridges cross the spring run; one at the mouth of the run and another
approximately 170 ft. upstream (Figure 2-6A). Midway between these two bridges there is
a weir across the spring run that has a rectangular opening near the middle (Figure 2-6B).
The top of the weir extends about 1½ to 2½ feet above the water surface in the run during
high tides. The opening is approximately 10½ ft. wide, with a bottom elevation of
approximately -0.7 ft. NGVD. All water discharging from the spring run to the Lower
Hillsborough River flows through this opening. The spring run above this wall is referred to
as the upper spring run, while the run below this wall is referred to as the lower spring run
(Figure 2-5).
The banks of the upper spring run are hardened by a seawall. Emergent vegetation is
present in front of the seawall over much of the north bank of the upper run (Figure 2-6C).
The entire southern shoreline of the upper run is un-vegetated, with the seawall extending
to the waters edge (Figure 2-6D). The shoreline of the lower run is not hardened, although
it is quite steep and rocky with emergent vegetation growing on much of the banks.
Greater details about the vegetation and other biological communities of the spring run are
described in Section 3.7 of this report.
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