The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
toward the end of the dry season. The implementation of an 18 cfs minimum flow during
relatively brief periods in the winter should thus have a very minor effect on the use of
the spring to augment the City's water supplies during water shortages.
Considering these factors, the minimum flows recommended in Section 5.4.1 should be
supplemented with a restriction that the minimum flow will be 18 cfs when water
temperatures in either surface or bottom waters in the Lower Hillsborough River near
the spring outfall are below 15 o C. The compete minimum flow recommendation for
Sulphur Springs is:
The proposed minimum flow for Sulphur Springs is 18 cfs. This minimum flow
may be reduced to 10 cfs during low tide stages in the lower Hillsborough River
if it does not result in salinity incursions from the Lower Hillsborough River into
the upper spring run. Salinity incursions shall be defined as when salinity values
in the upper spring pool are 1 ppt greater than the concurrent salinity value in
the spring pool. A minimum flow of 13 cfs can be implemented when water
levels in the Hillsborough River reservoir fall below 19 feet NGVD. This
minimum flow can be reduced to 10 cfs at low tide stages in the lower river if it
does not result in salinity incursions into the upper spring run. A minimum flow
of 18 cfs will be maintained if the temperature of either surface or bottom waters
in the Lower Hillsborough River near the mouth of the spring are below 15 o C.
5.6 Future data collection in support of the minimum flows
The proposed minimum flows will require much more intensive management of flows
from the spring than has been done in the past. The continuation of data recorders in
the spring pool, the upper spring run, and the lower Hillsborough River will be necessary
to determine if the management goals for salinity incursions and a thermal refuge are
met. These data will need to be available on a real-time for basis if the City chooses to
implement a tide-based 10 cfs minimum flow, or reduce the minimum flow to 13 cfs
during water shortages in cold months.
It is recommended that benthic invertebrates continue to be sampled periodically to
check the effectiveness of the minimum flows for maintaining invertebrate populations in
the upper spring run. Also, the proposed minimum flows and relationships of flows from
Sulphur Springs to the lower river should be examined as part of the re-evaluation of
minimum flows to the Lower Hillsborough River which are scheduled for completion by
2005.
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