The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
Executive Summary
The Southwest Florida Water Management District (the District) is directed by Florida
Statutes to establish minimum flows and levels for water resources within its jurisdiction.
Minimum flows are defined as "the limit at which further withdrawals would be
significantly harmful to the water resources or ecology of the area". By identifying the
hydrologic requirements of natural systems associated with a water body, minimum
flows serve as standards by which permitting or planning decisions can be made
concerning withdrawals from either surface or groundwater sources.
Sulphur Springs is an artesian spring that lies within a small park in a highly urbanized
setting in Tampa, Florida. The average flow of Sulphur Springs for the last twenty years
is 34 cubic feet per second (cfs) or 22 million gallons per day (mgd). For many years,
Sulphur Springs was a popular recreational resource that was used for swimming, but
problems with high bacteria counts closed the spring to swimming in the 1980s. Since
the 1960s, Sulphur Springs has been used as a back-up water supply source by the
City of Tampa to augment water supplies in the Hillsborough River Reservoir. The
mineral content of Sulphur Springs has been increasing since the 1970s and the spring
currently exceeds potable water standards for a number of constituents. However, by
blending the spring water with the supplies in the reservoir, the City can divert water
from the spring for limited periods of time. The spring, however, is only used during
impending water shortages, and withdrawals from the spring have occurred on only 11
percent of the days since 1991.
Sulphur Springs provides flows of low-salinity water that supports downstream biological
communities in the spring run and the Lower Hillsborough River. Until recently, periodic
withdrawals have had a major effect on flows from the spring pool. The pump for the
City's diversion facility operates at a rate (19.7 mgd) that is nearly as great as the
average flow of the spring. Consequently, during periods of withdrawal, flows from the
spring to the spring run and lower river were reduced to zero or very low rates of flow.
In 2001 the City modified the diversion facilities at Sulphur Springs so that variable
amounts of water can be diverted from the spring pool. These modifications were done
in part to meet the minimum flow rule for the Lower Hillsborough River, which stipulates
that 10 cfs (6.5 mgd) of water from Sulphur Springs can be diverted to the base of the
dam to meet minimum flows. The City now has the capability to simultaneously divert
variable amounts of spring water into the reservoir, to the base of the dam, and to the
spring run.
In 1999 the District began a series of studies to establish minimum flows for Sulphur
Springs with the understanding that the modified diversion facilities would be used to
manage springflow within a range that protects the biological communities in the spring
run and lower river from significant harm. Using the modified diversion facilities,
experimental flow tests were conducted to examine the downstream effects of a range
of flows from the spring pool. Data collection for these studies included the operation
of a series of continuous recorders in the spring run and lower river, water quality and
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