The Determination of Minimum Flows for Sulphur Springs, Tampa

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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 xiii
DRAFT biological sampling in the spring run, and hydrodynamic salt transport and thermal model simulations of the lower river. Data from previous and ongoing hydrobiolgical studies of the Lower Hillsborough River conducted by other agencies were also evaluated. Based on observed relationships between flows from the spring and the ecological characteristics of the spring run and the lower river, the District established three management goals for the determination of minimum flows for Sulphur Springs. These are: 1. Minimize the incursion of brackish water from the lower Hillsborough River into the upper spring run. 2. Maintain low salinity habitats in the Lower Hillsborough River 3. Maintain a thermal refuge for manatees in the Lower Hillsborough River during cold winter periods. Goal number 1 was developed to protect the abundance and diversity of the benthic macroinvertebrates in the upper spring run, which can be impacted by the incursion of high salinity water from the lower river at flow rates of springflow. The flow tests indicated a flow of 18 cfs (11.6 mgd) largely prevents the incursion of water from the lower river, except during very high tides. During times of water shortage flows could be reduced to 13 cfs (8.4 mgd), which will result in brief incursions of water from the river on high tides. Water levels of 19 feet in the Hillsborough River Reservoir should be used to identify times of impending water shortage. It was concluded that the invertebrate community would recover from these periodic incursions with the resumption of higher flows when water shortages end. Since the incursions of river water are related to tides, flow from the spring can be reduced to 10 cfs (6.5 mgd) at low tide stages in the river, if it does not result in the incursion of water from the river into the upper spring run. The minimum flows for goal number 1 were evaluated further to determine their effects on the salinity and thermal characteristics of lower river (goals 2 and 3) Modeling results indicate that the river benefits from higher flows, but the 18 cfs minimum flow combined with periodic use of 13 and 10 cfs minimum flows would be within acceptable limits for the prevention of significant harm. These minimum flows also meet the requirements of a thermal refuge for manatees in the lower river, provided that the minimum flow remain at 18 cfs if water temperatures in either surface or bottom waters in the lower river near the mouth of the spring drop below 15 degrees Celsius, equal to 59 degrees Fahrenheit. Based on these findings, the proposed minimum flow for Sulphur Springs is as follows: 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 river into the upper spring run. Salinity incursions shall be defined as when salinity values in the upper spring run are more than 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 xiv
Page 1 and 2: The Determination of Minimum Flows
Page 4 and 5: DRAFT TABLE OF CONTENTS List of Tab
Page 6: 4.5 Goal 1 - Minimize the incursion
Page 10 and 11: DRAFT LIST OF FIGURES Chapter 2 - P
Page 12 and 13: Fig. 3-13 Fig. 3-14 Fig. 3-15 Fig.
Page 14 and 15: Fig. 5-7 Fig. 5-8 Fig. 5-9 Fig. 5-1
Page 16 and 17: Acronyms and Definitions DRAFT AMO
Page 20: DRAFT below 19 feet NGVD of 1929. T
Page 24 and 25: CHAPTER 1 PURPOSE AND BACKGROUND OF
Page 26 and 27: DRAFT water, or aquifer, provided t
Page 28: DRAFT one the indicators were the f
Page 31 and 32: DRAFT The spring and its run lie in
Page 33 and 34: DRAFT Figure 2-3. Recent photograph
Page 35 and 36: 2 - 6 DRAFT
Page 37 and 38: DRAFT -5 -4 -3 -2 -1 0 1 2 3 0.4 4
Page 39 and 40: DRAFT 10.0 Yrly_Pumpage.grf 15 Annu
Page 41 and 42: DRAFT 1999 2000 2001 2002 2003 35 D
Page 43 and 44: DRAFT Figure 2-14. Return flow stru
Page 45 and 46: DRAFT 40 Jan. Feb. Mar. Apr. May Ju
Page 47 and 48: DRAFT due to withdrawals for public
Page 49 and 50: DRAFT Figure 2-19 . Temporal trend
Page 51 and 52: DRAFT Figure 2-20. Temporal trends
Page 53: DRAFT In comparison to specific con
Page 57 and 58: DRAFT average daily withdrawals for
Page 59 and 60: DRAFT Figure 2-25. Average specific
Page 61 and 62: DRAFT withdrawal rate of 31 cfs dur
Page 63 and 64: DRAFT Table 2-2. Sulphur Springs su
Page 65 and 66: DRAFT These plots indicate that his
Page 67 and 68: DRAFT CHAPTER 3 ECOLOGICAL RESOURCE
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DRAFT 3 Run_Riv_Stg.grf Water Surfa
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DRAFT 3.4 Salinity in the spring ru
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DRAFT 1999 2000 2001 2002 2003 2004
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DRAFT pumping events resulted in sa
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DRAFT As discussed in Section 2.5.3
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DRAFT tolerate and are frequently f
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DRAFT Appendix B are color coded to
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DRAFT habitat in the lower river pr
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DRAFT The FWC using a modified stra
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DRAFT increased with a return to no
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DRAFT 2000. The results from three
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DRAFT species (10 to 13) were colle
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DRAFT 1940 1950 1960 1970 1980 1990
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DRAFT . 1000.00 100.00 10.00 1.00 0
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DRAFT 3.9.2 The effects of flows fr
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DRAFT Data from the Tampa Bay Water
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DRAFT EPCHC Period of Record Data L
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DRAFT 35 30 1996 1997 1998 1999 200
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7 DRAFT Elevation (m) 1 0 -1 -2 -3
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8 24 25 29 DRAFT Figure 3-20, 3-21
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DRAFT Figure 3-22 HBMP & EPCHC 2000
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DRAFT of the river between the dam
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DRAFT 10 11 12 13 14 15 16 17 10 11
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DRAFT The HBMP project (PBSJ 2003)
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DRAFT xanthurus) red drum (Sciaenop
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DRAFT as manatees seek fresh water
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1999 2000 2001 2002 DRAFT 35 TmpSS_
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DRAFT Platt Street 1974-2002 Columb
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DRAFT Median and minimum water temp
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DRAFT Figure 3-31 1999 2000 2001 20
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DRAFT Figure 3-33 2001 2002 2003 20
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DRAFT CHAPTER 4 TECHNICAL APPROACH
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DRAFT The sum of these consideratio
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DRAFT It is the conclusion of this
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DRAFT criteria. The
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DRAFT reach of the river 50 meters
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DRAFT of the dam. The experiments w
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DRAFT Salinity incursions above the
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DRAFT Figure 5-3. A - D. Box and wh
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DRAFT The results of the vertical p
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DRAFT Sulphur Springs < 33 cfs, Hil
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DRAFT Other breakpoints in the data
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DRAFT 40 Percent of Observations -
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DRAFT It is possible that infrequen
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DRAFT The effects of tide stage on
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DRAFT medians rise to near -0.2 fee
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DRAFT Sulphur Springs < 33 cfs, Hil
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DRAFT Sulphur Springs on salinity d
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7 29 DRAFT Elevation (m) 0/0cfs 1 0
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23 24 24 25 25 29 DRAFT Figures 14,
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DRAFT Viewed strictly from the infl
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DRAFT water removed would fluctuate
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DRAFT euryhaline, there were also m
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DRAFT 01/90 01/93 01/96 01/99 01/02
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DRAFT the intent of that condition
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DRAFT included inflows to the model
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DRAFT Flows for Sulphur Springs wer
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DRAFT ∆T represents the differenc
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DRAFT Figure 25 Temp (C) 22 Histori
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DRAFT Figure 26 Temp (C) 24 22 Hist
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DRAFT Similar to the coldest period
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DRAFT 5.7. Consideration of future
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DRAFT Culter, J. 1986. Benthic Inve
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DRAFT Shafland, P. L. and K. J. Foo
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APPENDIX A (from Chapter 2) Time se
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Sulphur Springs Water Quality 1991-
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Appendix B. Presence of macroinvert
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Appendix C. Percent composition of
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Appendix C. Percent composition of
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APPENDIX D (from Chapter 3) Percent
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APPENDIX D. Percent composition of
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APPENDIX D. Percent composition of
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APPENDIX E (from Chapter 3) Abundan
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BARE SAND FILAMENTOUS ALGAE COMBINE
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APPENDIX F - HILLSBOROUGH RIVER TEM
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Appendix G Daily values for mean, m
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APPENDIX H (from Chapter 5) Time se
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Experiment Number 6
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Appendix I Daily values for minimum
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28FEB2000 9.8 0.0 1.9 9.7 7.8 . 18.
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12FEB2001 14.0 3.5 1.7 4.6 2.9 1.1
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The Determination of Minimum Flows for Sulphur Springs, Tampa

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