The Florida Institute of Phosphate Research was created in 1978 by the Florida Legislature (Chapter 378.101, Florida Statutes) and empowered to conduct research supportive to the responsible development of the state’s phosphate resources. The Institute has targeted areas of research responsibility. These are: reclamation alternatives in mining and processing, including wetlands reclamation, phosphogypsum storage areas and phosphatic clay containment areas; methods for more efficient, economical and environmentally balanced phosphate recovery and processing; disposal and utilization of phosphatic clay; and environmental effects involving the health and welfare of the people, including those effects related to radiation and water consumption.

FIPR is located in Polk County, in the heart of the central Florida phosphate district. The Institute seeks to serve as an information center on phosphate-related topics and welcomes infomration requests made in person, or by mail, email, or telephone.

Executive Director Paul R. Clifford

Research Directors

G. Michael Lloyd, Jr. -Chemical Processing J. Patrick Zhang -Mining & Beneficiation Steven G. Richardson -Reclamation Brian K. Birky -Public Health

Publications Editor Karen J. Stewart

Florida Institute of Phosphate Research 1855 West Main Street Bartow, Florida 33830

(863) 534-7 160 Fax: (863) 534-7165

http://www.fipr.state.fl.us

HYDROLOGIC INVESTIGATION OF THE PHOSPHATE-MINED UPPER SADDLE CREEK WATERSHED, WEST-CENTRAL FLORIDA

FINAL REPORT

Patrick Tara, P.E. Ken Trout

Mark A. Ross, Ph.D., P.E. Jeffrey G. Vomacka, P.E. Mark Stewart, Ph.D., P.G.

Center for Modeling Hydrologic and Aquatic Systems Department of Civil and Environmental Engineering

and Department of Geology

UNIVERSITY OF SOUTH FLORIDA TAMPA, FLORIDA 33620

Prepared for

FLORIDA INSTITUTE OF PHOSPHATE RESEARCH 1855 West Main Street Bartow, Florida 33830

Project Number: 95-03-118

FIPR Project Manager: Steven G. Richardson

November 2003

DISCLAIMER

The contents of this report are reproduced herein as received from the contractor. The report may have been edited as to format in conformance with the FIPR Style Manual. The opinions, findings and conclusions expressed herein are not necessarily those of the Florida Institute of Phosphate Research, nor does mention of company names or products constitute endorsement by the Florida Institute of Phosphate Research.

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PERSPECTIVE The FIPR Hydrologic Model (FHM) is an integrated surface and ground water computer simulation model that was developed as a tool for the assessment of the hydrologic impacts of mining and various land reclamation alternatives. The FHM also has great potential as a planning tool for designing wetland systems and for developing watershed reclamation or improvement plans. Construction of a highway, known as the Polk County Parkway, has resulted in the destruction or degradation of wetlands. Rather than mitigate those wetland losses by constructing numerous widely scattered "postage stamp" wetlands, it was proposed that larger wetland systems be constructed on mined lands at or near the Tenoroc Fish Management Area. This provided an opportunity to further calibrate and develop the FHM and also to use this computer simulation model to assist in the design and evaluation of various alternatives for watershed and wetland improvements. It has been observed that flows in the Peace River have declined. This has been attributed by various entities to reduced rainfall, to lower water tables due to groundwater pumping, or possibly to the effects of mining. The Saddle Creek watershed forms the northern headwaters of the Peace River. The project examined the hydrology of the Saddle Creek watershed, which contains large acreages of mined land, north of Lake Hancock. Hydrological data were collected to describe current hydrologic conditions and to further calibrate the FIPR Hydrologic Model. The project team worked in cooperation with the Upper Peace River Ecosystem Planning Committee (UPREPC), comprised of representatives from state, local and federal agencies, to examine the feasibility of constructing mitigation wetland systems on mined lands at or near the Tenoroc Fish Management Area. There was also interest in increasing flows (especially base flow) in the Peace River while also controlling flooding. Other FIPR funded hydrology projects that may be of interest to the reader:

• Reclaimed Phosphatic Clay Settling Area Investigation: Hydrologic Model Calibration and Ultimate Clay Elevation Prediction. FIPR Publication No. 03-109-176.

• Feasibility of Natural Treatment and Recharge of Wastewater and Surface

Waters Using Mined Phosphate Lands. FIPR Publication No. 03-113-186. Steven G. Richardson FIPR Reclamation Research Director

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ABSTRACT The upper Saddle Creek basin is a rapidly developing watershed to the east of Lakeland, Florida along the I-4 development corridor. Saddle Creek is tributary to the Peace River, which has experienced significant stream flow decline in the last few decades. This project sought to construct a model that could be used to investigate the hydrologic conditions (historical and proposed) of this previously mined, urbanizing basin. Among the objectives of this study was the investigation of feasibility of creating large-scale wetland mitigation and ecosystem restoration on reclaimed mine land, and the reestablishment of a more historical hydrologic function of the Saddle Creek watershed. Another important objective was the demonstration of the calibration and utility of the FIPR Hydrologic Model, FHM, for large-scale mine reclamation. A supplemental contract provided for additional data collection and flood plain modeling of the upper Saddle Creek. This supplemental scope was added in response to concerns from regulatory agencies as to the effects this wetland mitigation might have on the hydrology of areas downstream. This report documents the findings of this investigation and is being submitted jointly to the funding agencies. It summarizes the collection of hydrologic data and current hydrologic conditions of the basin. The report describes model set-up and calibration for both the large-scale domain and the near-field detailed model of Saddle Creek. The model has been utilized in a predictive capacity for hydrologic assessment of ecosystem restoration plans. Seven major restoration alternatives or basin evolutions were investigated with the model as examples. Conclusions or recommendations as to the best restoration alternatives and scheduling of final hydrologic investigations for the engineering design phase are delayed pending agency input. The model has shown to be productive for analyzing hydraulic impacts and benefits associated with wetland restoration alternatives in the Saddle Creek basin. The model has also shown to be a useful tool in analyzing large-scale mine land reclamation hydrology. However, several fundamental hydrologic questions are posed concerning the hydrology of west-central Florida mined lands, reasons for observed flow declines and drainage of the surficial aquifer.

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ACKNOWLEDGMENTS The researchers at USF would like to thank the Florida Fish and Wildlife Conservation Commission for their assistance in data collection and field reconnaissance and the use of facilities at the Tenoroc Fish Management Area and the FDEP Bureau of Mine Reclamation for their assistance. We would also like to thank the Florida Institute of Phosphate Research and the Department of Environmental Protection for providing the grants to make this research possible.

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TABLE OF CONTENTS PERSPECTIVE.................................................................................................................. iii ABSTRACT.........................................................................................................................v ACKNOWLEDGMENTS ................................................................................................. vi EXECUTIVE SUMMARY .................................................................................................1 INTRODUCTION ...............................................................................................................5 PROJECT OBJECTIVES ....................................................................................................7 MODEL DEVELOPMENT.................................................................................................9 Upper Peace River Far-Field Model ........................................................................9 Model Conceptualization .............................................................................9 Model Domain and Boundary Conditions .................................................10 Basins.............................................................................................10 Hydrography ..................................................................................10 Groundwater Grid Domain ............................................................13 Water Table....................................................................................13 Hydrostratigraphy ..........................................................................17 Initial Conditions ...........................................................................19 Meteorologic and Hydrologic Time Series................................................19 Rainfall...........................................................................................19 Evapotranspiration .........................................................................20 Streamflow/Baseflow Separation...................................................21 Groundwater Pumping Records.....................................................21 Spring Discharges ..........................................................................21 Simulation Period...........................................................................21 Surface Water Calibration..........................................................................21 Groundwater Calibration ...........................................................................22 Saddle Creek Near-Field Model ............................................................................45 Model Conceptualization ...........................................................................45 Geology..........................................................................................45 Historic Aquifer Data.....................................................................51 Model Domain and Boundary Conditions .....................................55

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TABLE OF CONTENTS (CONT.) Basins.................................................................................55 Hydrography ......................................................................55 Groundwater Grid ..............................................................55 Hydrostratigraphy ..............................................................60 Initial Conditions ...............................................................61 Meteorologic and Hydrologic Time Series....................................61 Rainfall...............................................................................62 Evapotranspiration .............................................................62 Streamflow/Baseflow Separation.......................................63 Lake Stages ........................................................................65 Groundwater Data Collection ............................................66 Groundwater Pumping Records.........................................73 Simulation Period...............................................................74 Surface Water Calibration..............................................................74 Groundwater Calibration ...............................................................88 Integrated FHM Calibration...........................................................91 ALTERNATIVE OR PREDICTIVE SIMULATIONS.....................................................97 Alternative 1 – Redirect Northwest Williams to Tenoroc Eastern Ditch ..............97 Alternative 2 – Redirect Southwest Williams to Western Ditch .........................104 Alternative 3 – Route Both Northwest and Southwest Williams to Eastern Ditch.............................................................................................................106 Alternative 4 – Route Both Northwest and Southwest Williams to Central Ditch.............................................................................................................106 Alternative 5 – Simulate Eastern Williams with Impervious Area......................123 Alternative 6 – Reroute Western Ditch to Shop Lake Then Shop Lake to Lake 2...........................................................................................................133 Alternative 7 – Addition of City of Auburndale WWTP Treated Waste Water............................................................................................................146 FLOOD PROFILE SIMULATIONS...............................................................................153 Introduction..........................................................................................................153 Model Background – HEC RAS..........................................................................153 Model Conceptualization .....................................................................................154 Reach Definition ......................................................................................154 Channel Cross-Sections ...........................................................................155 Structures .................................................................................................155

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TABLE OF CONTENTS (CONT.) Channel Roughness, Contraction and Expansion Coefficients................157 Flow Data and Boundary Conditions.......................................................158 Hydraulic Model Calibration ...............................................................................158 Hydraulic Model Results .....................................................................................159 CONCLUSIONS AND RECOMMENDATIONS ..........................................................161 Model Development and Calibration...................................................................161 Historical Trends in the Upper Saddle Creek Watershed ....................................162 Potential for Large-Scale Wetland Restoration ...................................................163 Application of the FHM for Large-Scale Mined Land Reclamation...................163 REFERENCES ................................................................................................................165 APPENDIX A Surveyed Cross-Sections .......................................................................... A-1 – A-6

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LIST OF FIGURES Figure Page 1. Far-Field (UPR) Model Basins and Basin Numbers.....................................11 2. Far-Field Hydrography and USGS Gaging Stations Used in UPR Model ...12 3. Far-Field and Near-Field Model Boundaries................................................14 4. Floridan Potentiometric Surface for May 1989 ............................................15 5. Floridan Potentiometric Surface for Sept. 1989 ...........................................15 6. Floridan Potentiometric Surface for May 1996 ............................................16 7. Floridan Potentiometric Surface for Sept. 1996 ...........................................16 8. Locations of SWFWMD Surficial Monitoring Wells in the Active Far-Field Model Domain .........................................................................17 9. Generalized Subsurface Geology and SWFWMD Stratigraphic Units ........18

10. Implementation of Hydrostratigraphic Units in the SWFWMD District-Wide Model ................................................................................18 11. Upper Peace River (Far-Field) Model Rainfall Stations (Hourly and Daily) .......................................................................................................20 12. Calibration Comparison at Saddle Creek at STR-P11..................................25 13. Calibration Comparison at Peace Creek Canal near Alturas ........................26 14. Calibration Comparison at Peace River at Bartow .......................................27 15. Calibration Comparison at Peace River at Fort Meade ................................28 16. Calibration Comparison at Bowlegs Creek near Fort Meade .......................29 17. Calibration Comparison at Payne Creek near Bowling Green .....................30 18. Calibration Comparison at Peace River at Zolfo Springs.............................31 19. Calibration Comparison at Charlie Creek near Gardner...............................32 20. Calibration Comparison at Peace River at Arcadia ......................................33 21. Calibration Comparison at Horse Creek near Myakka Head........................34 22. Calibration Comparison at Horse Creek near Arcadia .................................35 23. Calibration Comparison at Little Manatee near Wimauma ..........................36 24. Calibration Comparison at Little Manatee near Fort Lonesome ..................37 25. Calibration Comparison at North Prong Alafia at Keysville ........................38 26. Calibration Comparison at South Prong Alafia near Lithia..........................39 27. Calibration Comparison at Alafia River at Lithia.........................................40 28. Far-Field Model Layer 3 Target and Simulated Heads ................................43 29. Far-Field Model Layer 2 Target and Simulated Heads ................................44 30. Far-Field Model Leakance Between Layers 1 and 2 ....................................46 31. Far-Field Model Leakance Between Layers 2 and 3 ....................................47 32. Far-Field Model Layer 2 Transmissivity ......................................................48 33. Far-Field Model Layer 3 Transmissivity ......................................................49 34. Far-Field Model Layer 4 Transmissivity ......................................................50 35. Monitor Well Locations Near USCW...........................................................51 36. USGS Combee Road and State Road 33 Shallow Well ...............................52 37. USGS Combee and State Road 33 Intermediate Well..................................53 38. USGS Lake Alfred Floridan Well.................................................................53

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LIST OF FIGURES (CONT.) Figure Page

39. USGS Fish Lake Floridan Well ....................................................................54 40. USGS Tenoroc Road Floridan Well .............................................................54 41. Near-Field Sub-Basins and Model Classification.........................................56 42. Near-Field Hydrography and Model Classification......................................58 43. Near-Field Basins and Near-Field Grid Alignment ......................................60 44. Near-Field Basins, Rain Gage Locations and Thiessen Polygons................63 45. Near-Field Stream Gages..............................................................................64 46. Tenoroc Lake Staff Gages and Monitoring Well Locations.........................65 47. Penetrometer Results for Well S9.................................................................68 48. Penetrometer Results for Well S7.................................................................69 49. Penetrometer Results for Well S8.................................................................70 50. Penetrometer Results for Well S6.................................................................71 51. Penetrometer Results for Area North of Tenoroc Mine Road Opposite Shop .........................................................................................................72 52. Aquifer Elevations Measured During the Study Period ...............................73 53. Metered and Estimated Wells in the Near-Field Model Domain .................75 54. Station 11 Calibration (Lake 5 Inflows from Basins 9-13, 45).....................76

55. Station 13 Calibration (Lake 5 Outfall into Lake 4, Including Basins 9-13, 24, 25).............................................................................................77 56. Station 17a Calibration (Lake 2 Outfall into Central Ditch, Includes Basins 9-13, 23, 24, 27-29, 45)................................................................78 57. Station 17b Calibration, Downstream of Central and Eastern Con- fluence, Basins 5, 9-13, 23-30, 35, 45 .....................................................79 58. Station 19 Calibration, Eastern Ditch Before Tenoroc, Basins 5, 25 ...........80 59. Station 20 Calibration, Western Ditch, SW Corner of Tenoroc, Basins 1-4, 8, 17-22 .................................................................................81 60. Station 542, Saddle Creek at 542, Basins 1-35, 44, 45.................................82 61. Lake Stage Calibration Comparison, Picnic Lake ........................................83 62. Lake Stage Calibration Comparison, Lake 3 ................................................83 63. Lake Stage Calibration Comparison, Lake 4 ................................................84 64. Lake Stage Calibration Comparison, Lake 2 ................................................84 65. Lake Stage Calibration Comparison, Lake 5 ................................................85 66. Lake Stage Calibration Comparison, Lake Hydrilla.....................................85 67. Near-Field Leakance Distribution (Ft./Day/Ft.) ...........................................89 68. Near-Field Layer 1 Specific Yield Distribution............................................90 69. Near-Field Layer 3 Transmissivity Distribution...........................................92 70. Locations of Estimated Water Levels ...........................................................93 71. Observed and Simulated Surficial Wells ......................................................94 72. Observed and Simulated Floridan Wells ......................................................95 73. Simulated and Observed Potentiometric Surface Contours..........................96 74. Alternative Schematic – Alternative 1..........................................................98

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LIST OF FIGURES (CONT.) Figure Page

75. Discharge Comparison for Alternative 1 at Station 17a ...............................99 76. Discharge Comparison for Alternative 1 at Station 17b.............................100 77. Discharge Comparison for Alternative 1 at Station 19...............................101 78. Discharge Comparison for Alternative 1 at Station 20...............................102 79. Discharge Comparison for Alternative 1 at Reach 37 ................................103 80. Stage Comparison for Alternative 1 at Reaches 5 and 37 ..........................104 81. Alternative Scenario – Alternative 2...........................................................105 82. Discharge Comparison for Alternative 2 at Station 11...............................107 83. Discharge Comparison for Alternative 2 at Station 13...............................108 84. Discharge Comparison for Alternative 2 at Station 17a .............................109 85. Discharge Comparison for Alternative 2 at Station 17b.............................110 86. Stage Comparison for Alternative 2 at Reaches 17, 23, and 37 .................111 87. Alternative Schematic – Alternative 3........................................................112 88. Discharge Comparison for Alternative 3 at Station 11...............................113 89. Discharge Comparison for Alternative 3 at Station 13...............................114 90. Discharge Comparison for Alternative 3 at Station 17a .............................115 91. Discharge Comparison for Alternative 3 at Station 17b.............................116 92. Discharge Comparison for Alternative 3 at Station 19...............................117 93. Discharge Comparison for Alternative 3 at Station 20...............................118 94. Discharge Comparison for Alternative 3 at Reach 37 ................................119 95. Stage Comparison for Alternative 3 at Reaches 5 and 17 ..........................120 96. Stage Comparison for Alternative 3 at Reaches 23 and 37 ........................121 97. Alternative Schematic—Alternative 4........................................................122 98. Discharge Comparison for Alternative 4 at Station 11...............................124 99. Discharge Comparison for Alternative 4 at Station 13...............................125 100. Discharge Comparison for Alternative 4 at Station 17a .............................126 101. Discharge Comparison for Alternative 4 at Station 17b.............................127 102. Discharge Comparison for Alternative 4 at Station 19...............................128 103. Discharge Comparison for Alternative 4 at Reach 37 ................................129 104. Stage Comparison for Alternative 4 at Reaches 5 and 18 ..........................130 105. Stage Comparison for Alternative 4 at Reaches 23 and 37 ........................131 106. Alternative Schematic – Alternative 5........................................................132 107. Discharge Comparison for Alternative 5 at Station 11...............................134 108. Discharge Comparison for Alternative 5 at Station 19...............................135 109. Discharge Comparison for Alternative 5 at Station 20...............................136 110. Discharge Comparison for Alternative 5 at Reach 37 ................................137 111. Stage Comparison for Alternative 5 at Reaches 1 and 5 ............................138 112. Stage Comparison for Alternative 5 at Reaches 18 and 37 ........................139 113. Alternative Schematic – Alternative 6........................................................140 114. Discharge Comparison for Alternative 6 at Station 17a .............................141 115. Discharge Comparison for Alternative 6 at Station 17b.............................142

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LIST OF FIGURES (CONT.) Figure Page

116. Discharge Comparison for Alternative 6 at Station 20...............................143 117. Discharge Comparison for Alternative 6 at Reach 37 ................................144

118. Stage Comparison for Alternative 6 at Reaches 27, 30, and 37 .................145 119. Alternative Schematic – Alternative 7........................................................147 120. Discharge Comparison for Alternative 7 at Station 17a .............................148 121. Discharge Comparison for Alternative 7 at Station 17b.............................149 122. Discharge Comparison for Alternative 7 at Reach 37 ................................150 123. Stage Comparison for Alternative 7 at Reaches 24 and 25 ........................151 124. Stage Comparison for Alternative 7 at Reaches 27 and 37 ........................152 125. Saddle Creek Hydraulic Model Cross-Section Locations ..........................153

126. Simulated Water-Surface (WS) Elevations for Saddle Creek 25-Year and 100-Year Simulations......................................................................160 A-1. Surveyed Cross Sections 30000, 29000, 800, 700..................................... A-1 A-2. Surveyed Cross Sections 28000, 25000, 24000, 23000............................. A-2 A-3. Surveyed Cross Sections 22000, 21900, 21500, 21000............................. A-3 A-4. Surveyed Cross Sections 20900, 20700, 20600, 20400............................. A-4 A-5. Surveyed Cross Sections 20000, 17000, 16000, 15000............................. A-5

A-6. Surveyed Cross Section 14000 .................................................................. A-6

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LIST OF TABLES Table Page 1. Far-Field Basin to Reach Routing.................................................................23 2. Far-Field Reach-to-Reach Routing ...............................................................23 3. Calibration Comparison at Alafia River at Lithia.........................................24

4. Estimated Baseflow from 16 Gaging Stations and Model Simulated Baseflow ..................................................................................................42 5. Near-Field Basin to Reach Routing ..............................................................57 6. Near-Field Reach to Reach Routing .............................................................59 7. Monthly Lake Stages (in Feet NGVD) for Major Lakes in the Near-Field Domain (Values Identified with an Asterisk [*] Are Estimated) ............66 8. Calibrated Near-Field Subbasin Parameters ........................................... 86-87 9. Sub-Critical Flow Contraction and Expansion Coefficients.......................158 10. Calibration Results for the Hydraulic Model of Saddle Creek ...................159

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EXECUTIVE SUMMARY

The upper Saddle Creek basin is a rapidly developing watershed to the east of Lakeland, Florida along the I-4 development corridor. Saddle Creek is tributary to the Peace River, which has experienced significant stream flow decline in the last few decades. It is also a basin that has experienced extensive phosphate mining over the same time period. This study sought to develop a comprehensive coupled surface and groundwater computer model, known as the FIPR Hydrologic Model (FHM), to investigate the hydrology of the basin and the implications of large-scale mine reclamation within the catchment. It represents the first real test of the FHM on a regional watershed with extensive mine landforms. For this study, two model scales were developed: a far-field model of the upper Peace River system and a near-field model, which encompassed the detail of the Saddle Creek basin. The models were calibrated for a three-year data collection period and applied to investigate wetland restoration alternatives proposed within the Tenoroc Fish Management Area. The Upper Peace River far-field model was developed and calibrated for the purpose of defining the groundwater boundary fluxes and heads for the Saddle Creek near-field model. This model was initially based on a portion of the District-wide model developed for SWFWMD (Geurink and others 1995). The domain extended to approximate no-flow boundaries defined for the Floridan aquifer (i.e., the central highlands ridge, Gulf of Mexico, northern and southern streamline boundaries). Streamflow gages of the U.S. Geological Survey (USGS) at Peace Creek Canal, Peace River at Arcadia, Horse Creek at Arcadia, and Charlie Creek, formed the basis of surface water calibration of the model. The surface water basins originated from USGS 250000 scale quadrangles. These boundaries were then aggregated or further subdivided into 28 unique sub-basins, representing the entire Alafia and Little Manatee River watersheds, significant portions of the Peace River basin down to the USGS Arcadia station and small portions of the Hillsborough and Kissimmee River basins. The hydrography (wetlands, streams and lakes) for the Upper Peace River (UPR) far-field model originated from the USGS 1:100,000 scale quadrangle Digital Line Graphs (DLGs). Calibration of the hydrography parameters (i.e., rating, streambed conductance, and elevations) was performed in both the surface water simulations and groundwater simulations. The resulting groundwater discretization was a 28 row by 49 column grid with cells measuring 2 x 2 miles coincident with a portion of the SWFWMD District-wide model. In order to calibrate the FHM, meteorologic and time series hydrologic data pertaining to the domain were collected, re-formatted, and corrected (for missing or bad data). These temporal data include rainfall, streamflow, pan ET, lake stages, groundwater pumping records, spring discharges, and monitoring well elevations. The rainfall time series used in the surface water simulation were developed from both the available daily stations and hourly stations for the domain. Pan evaporation data were obtained from the Nation Weather Service (NWS) National Climatic Data Center

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(NCDC) Lake Alfred Station. The observed streamflow time series for each of the 16 calibration stations was obtained from the USGS daily records. Metered and estimated pumping well records were obtained from SWFWMD for the active groundwater domain. A total of 5,709 wells were identified. Known significant spring discharges were obtained from the USGS. The simulation period selected was from 1/1/1985 to 12/31/1995. This period was selected for the quality of data available. Using USGS streamflow records from 1980 to 1994, average baseflow contributions at the 16 gaging stations used in the surface water model were estimated using baseflow separation techniques advocated by Perry (1995) and Taylor (1997). These average baseflow values were used to calibrate the stream/aquifer response of the model. Using a statistically based, parameter-estimation procedure (PEST, Watermark Computing, 1994) and the above assumptions, a reasonable model calibration was achieved with, generally, improved performance towards the northern extent which includes the Saddle Creek Watershed. The Saddle Creek near-field model was developed (the focus of the study) to simulate the water budget of the Saddle Creek watershed upstream of Lake Hancock. The selected domain was defined by a combination of large-scale model domain and near-field sub-basins. The Upper Saddle Creek Watershed was used to define the domain of the calibrated surface water model. The Upper Saddle Creek watershed, USCW, was divided into 47 sub-basins. These basins were delineated from USGS 24,000 scale quads, available SWFWMD and mining aerials with topography, and from field surveys. Hydrography data were gathered from the following sources: (1) digitized for the project from recent aerials, (2) SWFWMD land use mapping, and (3) USGS/EPA RF3 (McKay and others 1994) hydrography coverage. To help calibrate the USCW model, bi-weekly field trips were made by USF personnel and monthly by USGS cooperators to record water levels in surficial wells, Floridan wells, and selected lakes. Site specific rainfall was collected continuously over the study period for this project. Pan evaporation was monitored by the USGS at the Eagle Lake station. Continuous streamflow measurements were made at seven locations within and around the Tenoroc area. The stations were located to capture the three major conveyances of the USC basin: Western, Central, and Eastern Ditches. Sites were identified representing both mined and unmined areas for the installation and monitoring of additional surficial observation wells for this project. Seven predictive alternatives were developed for possible basin and reach modifications that could improve the hydro-period of the Tenoroc Fish Management Area lakes and/or enhance existing wetlands or allow the creation of new wetlands. Alternative 1 was to take discharge from the northwest (Williams) parcel and re-route it to the Eastern Ditch. The northwest Williams parcel currently flows to the Western Ditch. It was concluded that further storage attenuation would be required, possibly by modifying the outfall of Lake 2 or the construction of additional wetlands or lakes, to make this alternative viable. Alternative 2 was to re-route the discharge from southwest Williams through the northwest Williams into the Western Ditch. Currently northwest Williams discharges to the Western Ditch, by-passing Tenoroc, while the Southwest

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Williams discharges to the Central Ditch into Lake 5. The model results indicated that, if this alternative was implemented, the Central Ditch at Station 11 would experience a 50% reduction in annual average discharge. Alternative 3 was to combine the discharge from both the northwest and southwest Williams parcels into the Eastern Ditch. This alternative resulted in overall increases in discharge at Stations 11, 13, 17a, 17b and 19. These stations represented both the Central and Eastern Ditches. Alternative 4, which required no basin parameter adjustments, considered re-routing both the northwest and southwest Williams to the Central Ditch. This alternative would affect the water budget at Saddle Creek Road (Central Ditch) primarily from changes in storage attenuation (timing and severity of discharges). Downstream at Saddle Creek Road there was little change in total discharge over the simulation period. Alternative 5 was to predict the hydrology after the eastern Williams tract is fully developed, implementing possible changes associated with a proposed DRI for this tract. Area and storage volume of surface water features in the eastern Williams tract were assumed to be reduced by 30% and the reduced area was added to the basin area, which represents filling of the lakes that presently exist. This alternative added 11% to the cumulative discharge at Saddle Creek Road. Only minor changes were made to the reach stages. Alternative 6: This alternative was designed to investigate re-routing the discharge from the Western Ditch, combined with discharges from Lakes G and F, into Shop Lake. Then Shop Lake would be re-routed to Lake 2. Cumulative discharges at Station 17a were found to be increased by 60% from the background simulation. A similar increase was shown at Station 17b, just downstream of 17a. Station 20 had a dramatic reduction in cumulative discharge. Alternative 7: The City of Auburndale is progressing with the construction of a spray field to discharge treated effluent adjacent to the Tenoroc Fish Management Area. This alternative sought to investigate the effects of this added inflow to the basin budget. The cumulative discharge at Station 17a was increased by 27%. The increase was more noticeable during the recession limbs of the hydrographs. The increase was also significant at Station 17b and Saddle Creek Road with 21% and 13% increases respectively. To evaluate the potential levels of flooding within the Saddle Creek watershed during the 25- and 100-year design storm events, a hydraulic (backwater) model was developed for the primary channel system from Saddle Creek Road to State Road 540 just north of Lake Hancock. The peak flows generated by the near-field surface water hydrologic model were input to the Saddle Creek hydraulic model to simulate the surface water profiles and flood profiles for the system. The computer program HEC-RAS (HEC-RAS 1998a,b) was used in the analysis to simulate the water surface profiles in the Saddle Creek for the seven alternatives. The results of the 25- and 100-year flood study analysis of Saddle Creek are presented in the Appendix. No adverse flooding potentials were noted downstream of Saddle Creek Road. During the period of observation, it was noted that water-table elevations and the elevations of the potentiometric surface of the Floridan Aquifer were highly correlated. This led to a conclusion that, at the scale of the near-field model representing the Tenoroc site, lateral flow in the surficial aquifer is not a major component of the groundwater system, but vertical flow between the surficial and Floridan Aquifers is. Therefore, the

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system is driven by surficial storage and significant flow declines may have resulted from surficial drainage, possibly from ditching and drainage from landform development (mining and urbanization) or from Floridan drawdown and quite possibly the combination. Historically, the Upper Saddle Creek watershed represented the lower extremity of the Green Swamp which forms the head waters of four major river systems in west central Florida: the Hillsborough, Alafia, Peace and Withlacoochee Rivers. It has been and is continuing to be developed. Identifying the particular or predominant mechanism for the flow decline, however, requires a more complete model study of the larger regional system as the boundary conditions for the USC model were seen to change during the period. The model calibration for the near-field model compared reasonably well to the observed data of the three-year period representing water table fluctuations and streamflow periodicity. Alternatives were investigated with the model to evaluate the potential for hydro-period restoration of the Upper Saddle Creek watershed. The alternatives range from relatively minor flow system alterations, landform changes, to significant re-routing of the principal tributaries. Predicted simulations were made for the various alternatives and results presented in terms of full hydro-period restoration. This test of the FHM demonstrated the utility, advantages and requirements of a comprehensive integrated surface and groundwater model for evaluating the hydrology of mined and urbanizing land in West-Central Florida. The calibrated model product has been distributed to the public user community, consultants and regulatory agencies for continued calibration and predictive use as a principal product of this effort.

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INTRODUCTION The Upper Saddle Creek Watershed (USCW), tributary to the Peace River, drains the northern portion of the central Florida phosphate mining district. A progressive long-term decline of discharge in the Peace River has occurred (Hammett 1990, Taylor 1997). It has been speculated that the altered drainage systems associated with surface mining may have contributed to the decline. It is also suggested that development in the watershed may have affected flows. At the time of this report, the Florida Department of Transportation (FDOT) has in progress two major highway projects that will affect wetlands within the Saddle Creek watershed. An ad hoc working group of state and federal agency representatives has been formed. This group is charged with developing ecosystem management action plans and improving the hydrologic function of the upper Peace River, including the Saddle Creek. The Upper Peace River Ecosystem Planning Committee (UPREPC) has as an early task directing the construction of mitigated wetlands within the watershed for the FDOT and reclamation of mined lands to achieve more stable surface water flows in the USCW. The Tenoroc Fish Management Area lies within the upper portion of the Saddle Creek basin. The Tenoroc site is approximately 10 square miles of previously mined lands donated to the State and managed by the Florida Fish and Wildlife Conservation Commission (FFWCC). The primary concern of UPREPC, FDOT, and FFWCC is how the drainage patterns on mined lands in the Saddle Creek area can be improved to support additional high-quality wetlands and enhance the hydrologic function of the USCW. These wetlands would be developed as mitigation for wetlands disturbed or destroyed by FDOT during construction of the Polk County Parkway and the widening of Interstate 4. The large-scale mitigation would also enhance wildlife habitat, create a habitat corridor, and improve the ecosystem function at Tenoroc. Another matter of public concern is how drainage patterns can be improved to increase dry season flows to Saddle Creek and the Peace River, while minimizing flooding of residential and commercial areas (perhaps through use of wetlands for attenuation). Another issue is aquifer recharge. Has it been affected by the development and mining of the basin and can it be increased (again to alleviate flooding and to enhance downstream potable water supply)? The UPREPC, FFWCC, FDOT, and the Florida Department of Environmental Protection (FDEP) have proposed, as an integral part of wetland mitigation, to improve surface drainage from the reclaimed phosphate-mined land at and adjacent to the former Tenoroc Mine area and increase streamflow to Saddle Creek and to the Peace River. A study was necessary to determine present hydrologic conditions and drainage patterns prior to development of a drainage improvement plan and restoration of more functional interconnected wetlands. The FIPR Hydrologic Model (FHM) has evolved to become a useful tool to help assess these interests. A regional FHM application and demonstration of large-scale mining reclamation was strongly warranted to further validate the model with the regulatory community.

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This project demonstrates the utility of the FHM integrated surface water/groundwater model as a tool to assess large-scale landform restoration and gain better understanding of regional hydrologic processes. The result of this study is a complete database including spatial data in ARC/INFO GIS format, and hydrologic data for the basin. Another product is the ability to rate and classify the performance of the various wetland restoration scenarios. With this information a more enlightened perspective can be made toward the design and consequent construction of the wetland restoration and/or mitigation within the Saddle Creek basin.

7

PROJECT OBJECTIVES

The five major objectives of this study were: (1) construct an integrated model of the basin that will aid in the wetland design process and be a basis to compare and measure the performance and benefits of wetland design alternatives; (2) demonstrate the calibration and utility of the FIPR Hydrologic Model (FHM) for regional hydrologic investigations and landform restoration; (3) provide predictive assessment capabilities of both surface water and groundwater flows to Saddle Creek and Lake Hancock; (4) evaluate existing and proposed alternative interconnected wetland systems in the upper Saddle Creek Basin; and (5) compare and contrast present day and historic hydrology and hydrography of the upper Saddle Creek Basin.

9

MODEL DEVELOPMENT The scope of the project included the development of an integrated surface water and groundwater model of the Upper Saddle Creek Watershed (USCW) to define and simulate the hydrology of the watershed. To create boundary conditions for the USCW groundwater model, a far-field, large-scale model was constructed which extends to no-flow, constant head, and head-dependent flux boundaries. This large-scale model, the Upper Peace River (UPR) model, was then used to define the temporally variable and flow-dependent boundaries of the smaller-scale model of the Upper Saddle Creek Watershed. UPPER PEACE RIVER FAR-FIELD MODEL The Upper Peace River far-field model was developed and calibrated for the purpose of defining the groundwater boundary fluxes and heads for the USCW near-field model. A surface water component was developed to produce recharge rates defined through the simulation of the surface water budget. These recharge rates were then used to define the recharge boundary condition of the groundwater model. Calibrated parameters from the far-field model were used as starting values for the near-field calibration. Model Conceptualization An important requirement in the creation of a groundwater model is the delineation of groundwater fluxes at the model boundaries. During the initial model conceptualization, the intention was to obtain groundwater boundary fluxes for the Saddle Creek watershed from the SWFWMD District-wide model (Ross and others 1997). However, the District-wide model, was not fully calibrated, and could not provide useful boundary fluxes without additional calibration. Rather than attempt a calibration of the entire SWFWMD District-wide model, a prohibitive undertaking within this project scope and budget, a far-field model domain limited to the greater mining district was developed. This model was initially based on a portion of the District-wide model which would minimize the calibration area but would only extend to well defined groundwater and surface water boundaries. Although the creation and calibration of a new far-field model was beyond the scope of the original project proposal, it was believed that this process would provide more reliable boundary flux information for the USCW while still remaining within the project schedule. Calibration using a statistically based, parameter-estimation procedure (PEST; Watermark Computing 1994) suggested that insufficient information was available to create a statistically rigorous far-field model for fully dynamic fluxes. For this reason, calibration of the far-field model provided conductances and transmissivities for the near-field model, but reliable values could not be obtained for fluxes between the far-field and near-field models.

10

Model Domain and Boundary Conditions

The selected model domain for the UPR model was defined by the observed characteristics of the west-central Florida groundwater system. The domain extended to approximate no-flow boundaries defined for the Floridan Aquifer. These boundaries were then expanded slightly to include the entire catchment for the following U.S. Geological Service (USGS) streamflow gages: Peace Creek Canal, Peace River at Arcadia, Horse Creek at Arcadia, and Charlie Creek. A detailed description for each defined boundary condition is included below. Basins

The surface water basins were defined using boundaries developed by the USGS. These basin boundaries were delineated from 1:250,000 scale quadrangles. These boundaries were then aggregated into 28 unique sub-basins. These sub-basins represented the entire Alafia River and Little Manatee River catchments and significant portions of the Peace River basin down to the USGS Arcadia station and small portions of the Hillsborough River basin and Kissimmee River basin including other small coastal basins. Figure 1 shows the far-field model basins used in model calibration. The sub-basin delineation include closure at a total of 16 USGS long-term flow stations (Figure 2) for use in calibration. The original USGS basins were modified slightly to represent only those portions that contribute to the gage records used for model calibration. Hydrography

The simulated hydrography for the Upper Peace River (UPR) far-field model originated from the USGS 1:100,000 scale quadrangle Digital Line Graphs (DLG). The EPA used this coverage as a basis to develop the Reach File Version 3 (RF3) (McKay and others 1994) hydrography coverage. This hydrography has routing attributes that were used to develop a Strahler-based order (Strahler 1957) for each hydrography element. This order attribute was then used to define the reach parameters such as width, depth to top of bank, and side slopes. This technique, as well as the parameters, was developed as a consequence of research for SWFWMD (Ross and others 1997). These hydrography elements were aggregated and classified into the hydrography cover utilized in the model shown in Figure 2. All hydrography was utilized in the model in the form of either storage attenuation reaches or routing reaches in HSPF (Ross and others 1997). Storage attenuation reaches provide the dispersed collection and principal attenuation of runoff and baseflow from the individual catchments. Routing reaches are typically larger conveyance features that accumulate and route the attenuated flow hydrographs to the outfall of the modeled domain. All available hydrography was utilized in the groundwater component of the model to determine baseflow rates. Calibration of the hydrography parameters (including rating, streambed conductance, and elevations) was performed in both the surface water simulations and groundwater simulations. The surface water simulation allowed modification of the stage storage and stage discharge relationships. The groundwater calibration resulted in refinement of the river cell bed elevation and the river bed conductances.

Figure 1. Far-Field (UPR) Model Basins and Basin Numbers.

11

Figure 2. Far-Field Hydrography and USGS Gaging Stations Used in UPR Model.

12

13

Groundwater Grid Domain To establish the extent of the far-field model within the district-wide grid, the

following boundaries were sought in order of importance: physical barriers to groundwater flow, hydrologic barriers that are persistent over time, and boundaries than could be represented as head-dependent fluxes. Because groundwater flow in the surficial aquifer is primarily downward (in comparison to the Floridan aquifer, there is relatively little horizontal flow in the surficial aquifer), hydrologic boundaries on the north, northeast, and northwest were based on the potentiometric contours of the Floridan aquifer. The resulting model domain is a 28 row by 49 column grid with cells measuring 2 miles by 2 miles coincident with a portion of the SWFWMD District-wide model. Within that grid is an irregularly shaped active groundwater domain (see Figure 3). The western boundary of the active domain is the physical barrier of the Gulf of Mexico. The northern and eastern boundaries are persistent hydrologic divides caused by groundwater flow from the topographically high Green Swamp recharge area of Polk county to the north and bounded by the Lake Wales Ridge on the east. The southern boundary was extended to the best hydrologic barrier that could be located; however, this is the least reliable of the boundaries and was modeled as a head-dependent flux boundary. This is also one of the most distant boundaries and, as such, may not have much effect on the USCW area (see Figure 3). The far-field model boundaries and the Floridan potentiometric surface are illustrated in Figures 4 through 7 for both the May 1989 and 1996 (depressed) surface and the September 1989 and 1996 (elevated) surface. The selected boundaries were positioned over very consistent and stable natural flow divides. These boundaries are best represented in the model with no-flow conditions.

Water Table SWFWMD monitors water-table elevations at 25 sites within the far-field model

domain. Most of these sites are located on the Lake Wales Ridge (Figure 8), leaving a large portion of the model area with no water-table data. Because the water-table elevation plays an important role in recharge and flux between the surficial and lower aquifers, and the surface and groundwater system, a better distribution of water-table elevation was necessary to adequately constrain the model. A new topography and water table GIS coverage was generated for the far-field model. The older topography coverage, developed from the USGS 250k quadrangles, was found to be inadequate for this study. The new coverage was developed from the 24k quadrangle contour lines. These contour lines were converted into a TIN (triangular irregular network), then converted into a lattice (regularly spaced grid) which extended throughout the far-field domain. The water table was created using the assumption that the water table intersects the land surface at the edges of lakes and wetlands. The hydrography coverage was converted into a point coverage which was intersected with the new topography lattice. The water table point coverage was then converted into a surface for use in the model calibration. Also generated was a distribution of depth-to-water table for the domain which could be used to define the nominal vadose zone or unsaturated zone thickness throughout the model domain.

14

Figure 3. Far-Field and Near-Field Model Boundaries.

15

Figure 4. Floridan Potentiometric Surface for May 1989. Figure 5. Floridan Potentiometric Surface for Sept. 1989.

16

Figure 6. Floridan Potentiometric Surface for May 1996. Figure 7. Floridan Potentiometric Surface for Sept. 1996.

17

Figure 8. Locations of SWFWMD Surficial Monitoring Wells in the Active Far-Field

Model Domain.

Hydrostratigraphy The groundwater component of the far-field model is based on the SWFWMD

district-wide model (Ross and others 1997). The model consists of four hydrostratigraphic units (Figure 9). The top unit, the surficial aquifer, is composed of sand, silty-sand and some clay. The subsurface units dip to the south but vary little in the east-west direction in the Saddle Creek area. The second unit represents the Hawthorn Group. This unit contains a clayey confining bed which is missing or discontinuous in the northern model region, including the Tenoroc and Saddle creek area, but thickens and becomes continuous toward the south. As this unit thickens, a limestone intermediate aquifer develops. Below the second hydrostratigraphic unit is the top of the Upper Floridan aquifer. The third unit, which begins the Floridan aquifer, is the Tampa/Suwannee Limestone and the Ocala Formation. The fourth hydrostratigraphic unit representing the lower portion of the Upper Floridan aquifer is comprised of the Avon Park Formation. These hydrostratigraphic units are implemented in the model as four layers representing the surficial, intermediate, and the two upper layers of the Floridan Aquifer (Figure 10). Fluxes into and out of hydrostratigraphic layer 2, including the intermediate aquifer, are accommodated in the district-wide model by adjusting the leakance terms at the upper and lower boundaries (arrows in Figure 10). The intermediate aquifer does not exist (at least as a continuous unit) in the upper portion of the USCW and, therefore, the leakance and transmissivity values for layer 2 in that area reflect a confining unit only.

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INTERMEDIATE AQUIFER

Figure 9. Generalized Subsurface Geology and SWFWMD Stratigraphic Units. SURFICIAL AQUIFER HS LAYER 1 “UPPER” FLORIDAN AQUIFER (Tampa/Suwannee) HS LAYER 3 (Ocala) “LOWER” FLORIDAN AQUIFER (Avon Park) HS LAYER 4 Figure 10. Implementation of Hydrostratigraphic Units in the SWFWMD

District-Wide Model.

HS LAYER 2

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Modifications to surface elevations (top and bottom of aquifer layers 1, 2, and 3) from the SWFWMD database were made using the improved topographic data for the region and well logs from SWFWMD ROMP wells.

Initial Conditions To provide a steady-state calibration target, an average Floridan and Intermediate

potentiometric surface was created for 1989 using May and September potentiometric data. SWFWMD has demonstrated that the average May and September water levels provide a reasonable approximation of the average annual Floridan potentiometric surface. The estimated water table elevations derived from the previously described procedure were used as the steady-state water table elevation. Hydrography coverages for the groundwater model were updated to include all hydrography (at the 100k quad scale) for the model domain. The hydrography elevations were also corrected using the topography coverage. Meteorologic and Hydrologic Time Series

In order to calibrate the FHM, meteorologic and time series hydrologic data pertaining to the domain were collected, reformatted, and corrected (for missing or bad data). These temporal data include rainfall, streamflow, pan ET, lake stages, groundwater pumping records, spring discharges, and monitoring well elevations. The data were obtained from many agencies utilizing various formats. It was necessary to reformat the data into a form that could be utilized to calibrate the model. Also, as field data collection is problematic, records are often plagued with missing and invalid data entries. These invalid or missing data time series were corrected before they were used in the model. Correcting data often involved either using data from another available and reasonable station or through linear interpolation. Rainfall

The rainfall time series used in the surface water simulation was developed from both the available daily stations and hourly stations for the domain. Sixteen daily stations and six hourly stations were available for the analysis (see Figure 11). The daily stations were aggregated into 10 discreet domains using the combined hourly and daily station Thiessen polygons. The daily rainfall for these discreet domains were then averaged (area weighted) to produce a representative rainfall for each of the ten domains. The daily rain data were then distributed into an hourly rain time series using the hourly distribution found in the nearest observed hourly station. This technique provided the best spatial and temporal representation of rainfall for each of the 10 domains. The Thiessen polygons of the 10 domains where then overlaid with the basin to provide a scaling for the stations found in each basin. The rainfall data were converted into a HSPF PLOTGEN format. This file was then imported into a HSPF WDM file format for faster simulation times.

20

Figure 11. Upper Peace River (Far-Field) Model Rainfall Stations (Hourly and

Daily).

Evapotranspiration Pan evaporation data were obtained from the Nation Weather Service (NWS)

National Climatic Data Center (NCDC) Lake Alfred Station (station number 4707). The PAN ET data were recorded using a daily time step. This time series was converted into a HSPF PLOTGEN file format. The time series was finally stored in the HSPF WDM file format, to reduce simulation times. Within the HSPF run data set, the pan evaporation record was multiplied by a 0.7 pan coefficient to estimate potential ET in the simulation.

21

Streamflow/Baseflow Separation The observed streamflow time series for each of the 16 calibration stations (see

Figure 2) were obtained from the USGS database using a daily time step (daily average). These data were used in the estimation of the runoff and baseflow components observed at each station. This separation is required in order to determine the calibration targets for the basin runoff and baseflow. The separation was performed using a moving window of minimums which are then averaged using another moving window. The length of the window is based on the storage capacity and size of the basin. The window length used in this analysis was 30 days long.

Groundwater Pumping Records Metered and estimated pumping well records were obtained from SWFWMD for

the active groundwater domain. A total of 5,709 wells were identified. An FHM HydroGIS utility distributed the well withdrawals between the four model layers based on the well depth, cased interval, diameter, and location. The result was 9,178 point withdrawal sources associated with specific model layers. Average daily withdrawals from each source were calculated for the steady-state model input.

Spring Discharges Spring discharges were obtained from the USGS. These records include seasonal

observed discharges that were interpolated to daily average discharges. These records were used to determine the parameters for the drain package representing the springs. The springs gaged by the USGS include Lithia Springs and Buckhorn Springs. The spring discharges did not effect the surface water calibration because all springs were downstream of USGS stream gages.

Simulation Period The simulation period selected was from 1/1/1985 to 12/31/1995. This period

was selected for the quality of data available. It was also highly desirable to select a sufficiently long simulation period so that the simulation initial conditions did not interfere with the simulation results and therefore parameter calibration. This period also cycles through several wet and dry periods for calibration through both extreme conditions. Surface Water Calibration

The far-field model was calibrated using 16 USGS streamflow gages (see description above): three within the Alafia watershed, 11 within the Upper Peace River watershed, and two within the Little Manatee Watershed. The watersheds were divided into 28 sub-basins with 38 inter-connected routing and storage/attenuation reaches (see

22

description above). The routing information for each basin and each reach is listed in Tables 1 and 2. The model used hourly time steps for both basin and reach water budget simulations. The GIS database was utilized to develop initial approximations of the model parameters. These parameters where modified during the calibration process in order to improve the match between the simulated and observed streamflow. Figures 12-27 show calibration results with two graphs for each calibration station. The first line graph demonstrates the comparisons between observed and simulated daily average stream flows. The second graph shows comparisons between observed and simulated cumulative streamflow and baseflow. There is generally good agreement between model predicted runoff and measurements throughout the domain. Also there was good consistency in prediction and observations of an overall trend towards increasing streamflow (runoff and baseflow) progressing south and west in the model domain. Simulated actual ET (AET) was maintained within a range of 37-39 inches. Calibration was performed from the upper most gages down to the outfall to isolate parameter adjustments for the domains between observation points. The calibrated basin parameters are listed in Table 3. Reach calibration was not required for the far-field model. This is because the far-field model was calibrated only sufficiently to improve the boundary conditions of the near-field model. Reach calibration only affects the timing and shape of stream discharge hydrographs and does not significantly affect recharge and groundwater heads or fluxes. Reach simulations were performed for peace-of-mind only. Even with very little calibration, the reach simulations compare fairly well to observed hydrographs. A few of the problems with the reach simulations are the “topping out” of the defined reach F-Table, shown as long flat spots in the simulated hydrographs. USGS ratings were used to define the stage discharge relation of the F-Table therefore the remaining calibration parameters are stage storage and stage area (which are interrelated). The far-field model was developed prior to the availability of detailed hydrography coverages (see near-field hydrography section below). The detailed hydrography should be included to improve the far-field model calibration (see recommendations at the end of this report). Groundwater Calibration

To facilitate model calibration, PEST, a commercial non-linear parameter optimizing program was utilized. PEST allows different parameter configurations to be tested automatically. Since each parameter test requires the model to be run hundreds of times, many more configurations can be tested with an automated approach. The PEST objective function is the sum-of-squares residual between the calibration targets and model-generated values. For each model run, PEST adjusts the variable parameters between predetermined ranges until the objective function has been minimized. Valid parameter ranges are entered prior to model execution based on SWFWMD aquifer tests, SWFWMD district-wide model data, and U.S. Geological Survey data. Recharge and evapotranspiration range values are derived from the HSPF surface water model, maintaining water balance. The parameter ranges ensure that the resulting calibration is based on reasonable parameter values.

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Table 1. Far-Field Basin to Reach Routing. Table 2. Far-Field Reach to Reach Routing.

Basin Reach Basin Reach 1 1 11 18 2 2 12 23 3 7 13 24 3 5 14 26 5 9 15 27 6 10 16 28 7 12 17 31 9 14 18 33 8 16 19 34 10 20

Reach Reach Reach Reach 1 3 18 19 2 3 19 22 3 11 20 22 4 7 21 22 5 8 23 25 6 8 24 25 7 8 26 30 8 11 27 29 9 11 28 30 10 11 29 30 11 15 30 32 12 13 31 32 13 15 33 35 14 17 34 37 15 17 35 37 16 17 36 37 17 19

Table 3. Calibrated Far-Field Subbasin Parameters.

Basin # LZSN INFILT LSUR SLSUR INFEXP INFILD UZSN NSUR LZS

1 15.760 0.150 328.9 0.0043 4.600 2.000 0.220 0.29900 15.760

2 17.420 0.150 238.2 0.0056 4.600 2.000 0.220 0.31880 17.420

3 18.410 0.250 253.8 0.0067 4.600 2.000 0.150 0.28200 18.410

4 18.930 0.130 200.0 0.0066 4.600 2.000 0.110 0.30440 13.930

5 15.400 0.250 288.4 0.0075 4.600 2.000 0.300 0.28840 15.400

6 20.000 0.100 250.0 0.0079 2.600 2.000 0.280 0.22630 20.000

7 16.750 0.110 250.0 0.0060 4.600 2.000 0.130 0.31000 16.750

8 11.900 0.035 141.3 0.0056 5.000 2.000 0.100 0.20310 11.900

9 16.610 0.071 232.9 0.0055 4.600 2.000 0.120 0.27900 16.610

10 13.000 0.070 313.2 0.0036 6.600 2.000 0.110 0.20860 13.000

11 7.910 0.100 293.1 0.0035 2.600 2.000 0.210 0.33150 7.910

12 10.000 0.090 350.0 0.0028 2.600 2.000 0.200 0.24870 10.000

13 6.060 0.075 250.9 0.0023 2.600 2.000 0.100 0.24510 6.060

14 15.400 0.045 205.0 0.0063 4.000 2.000 0.100 0.22410 15.400

15 11.220 0.075 220.0 0.0053 6.000 2.000 0.110 0.24320 11.220

16 16.800 0.120 263.8 0.0058 6.000 2.000 0.250 0.29580 16.800

17 17.570 0.040 221.6 0.0067 6.000 2.000 0.110 0.29560 17.570

18 14.230 0.105 246.1 0.0057 2.600 2.000 0.140 0.31010 14.230

19 14.200 0.070 217.3 0.0057 5.600 2.000 0.110 0.31890 14.200

20 5.850 0.090 222.2 0.0037 3.600 2.000 0.110 0.31260 5.850

21 10.320 0.090 210.1 0.0043 5.300 2.000 0.150 0.27540 10.320

22 13.145 0.120 211.7 0.0031 5.300 2.000 0.180 0.25000 13.145

23 18.838 0.140 207.7 0.0038 5.300 2.000 0.200 0.25000 18.838

24 30.400 0.150 218.7 0.0035 5.300 2.000 0.200 0.25000 30.400

25 14.110 0.170 215.0 0.0027 5.300 2.000 0.215 0.26490 14.110

26 28.600 0.170 220.6 0.0066 4.450 2.000 0.200 0.28820 28.600

27 6.190 0.075 210.7 0.0035 5.300 2.000 0.110 0.31890 6.190

28 4.800 0.035 211.4 0.0033 5.300 2.000 0.120 0.29860 4.800

24

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41

Using USGS streamflow records from 1980 to 1994, average baseflow contributions at the 16 gaging stations used in the surface water model were estimated using baseflow separation techniques advocated by Perry (1995) and Taylor (1997). These average baseflow values were used to adjust stream bed conductance in order to calibrate the model response in the steady-state model. Table 4 shows the results of the calibration with surficial aquifer heads fixed at the estimated water-table elevations.

The surficial aquifer has relatively little lateral flow; the SWFWMD district-wide model (Ross and others 1997) has surficial hydraulic conductivity values between 1 and 40 feet per day. In the far-field model domain, the SWFWMD district-wide model predominately has values between 8 and 12 feet per day. With the narrow range of hydraulic conductivity values and the model being relatively insensitive to moderate changes in these values, the hydraulic conductivity of model layer one was set to 10 feet per day. The transmissivity will, of course, vary with the thickness of layer one. Using PEST and the above assumptions, a reasonable model calibration was achieved (Figures 28-29), especially in the northern area which includes the Saddle Creek Watershed. However, the aquifer head in one of the model layers was held constant. When all four layers were made active (aquifer heads were allowed to fluctuate), the model simulation was unstable and would not converge to a solution. However, when the heads in any one of the model layers were held constant the model stabilized and converged. As the data for surficial aquifer water levels were derived principally from elevations of mapped surface water bodies, layer one (surficial aquifer) heads were fixed in order to get the far-field model to converge. It is assumed that the failure of the far-field model to converge with all layers active is the result of having insufficient head data to constrain the solution. Except for uncertainty in some boundary fluxes, the far-field model is believed to provide reasonable parameter values for use in the near-field model. Results from the preliminary calibration of the far-field model, holding heads in layer one constant, are illustrated in Figures 28-29. Figure 28 shows contours of the target average heads in layer and the simulated heads. Figure 29 illustrates contours of the average heads and simulated heads in layer 3 (layer 3 and layer 4 are assumed to have the same heads in the far-field domain). Figures 30 and 31 illustrate the leakance distribution between layers 1 and 2, and between layers 2 and 3 respectively. In the northern portion of the modeled area where the intermediate aquifer does not exist, the leakance between layers 2 and 3 is set to 10 feet/day/foot (or 1/day), a very high value, causing water at the boundary to immediately be moved from model-layer one to model-layer three, and the transmissivity is set to zero, preventing lateral flow in model-layer two. This, in effect, removes model-layer 2 from that region. Little confinement exists between layers 3 and 4 in the model domain and, hence, the leakance between layers 3 and 4 is set to 0.1 per day. The transmissivity distributions for layers 2, 3, and 4 are illustrated in Figures 32-34.

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Table 4. Estimated Baseflow from 16 Gaging Stations and Model Simulated Baseflow.

Estimated (cfs) Simulated (cfs) Reach Baseflow Cum. Baseflow Cum.

1-3 9.10 9.10 9.02 9.02 4 3.10 12.20 4.88 13.90 5 24.28 36.48 24.38 38.28

6-9 19.56 56.04 20.60 58.88 10-11 7.39 63.43 7.20 66.08

12 5.99 69.42 6.39 72.47 16 40.98 110.40 40.14 112.61

13-15,17 81.46 191.86 81.41 194.02 18-19 36.46 228.32 37.26 231.28

20 53.60 281.92 55.21 286.49 23 5.40 5.40 5.22 5.22

24-25 28.79 34.19 29.40 34.62 26 41.89 41.89 39.49 39.49 27 35.51 77.40 33.81 73.30

28-30 32.58 109.98 31.09 104.39 33 5.68 5.68 6.13 6.13

34-35 46.42 52.10 43.11 49.24

43

Figure 28. Far-Field Model Layer 3 Target and Simulated Heads.

44

Figure 29. Far-Field Model Layer 2 Target and Simulated Heads.

45

SADDLE CREEK NEAR-FIELD MODEL The Saddle Creek near-field model was developed to simulate the water budget of the Saddle Creek watershed upstream of Lake Hancock. Selection of this area allowed adequate resolution while maintaining a sufficient domain for investigating future wetland mitigation alternatives. Data were collected specifically for the calibration of both surface and groundwater domains. A description of the available data and the model calibration follows. Model Conceptualization Geology

The most extensive published survey of the geology in the Saddle Creek Watershed is by Cathcart (1964). He used well logs from phosphate mining companies and exposures in active mine pits to assemble a series of cross-sections and fence diagrams, primarily in townships 27 and 28 south and ranges 24 and 25 east. According to Cathcart, the surficial deposits are primarily, loose, quartz, medium to fine-grained, well-sorted Pleistocene terrace sand with some recent windblown sand and swamp muck. The terrace sand is about 60 feet in thickness on the western ridge and thins to the east. Below the surficial sand is the Pliocene Bone Valley Formation (now classified as the Bone Valley Member of the Peace River Formation of the Hawthorn Group). Cathcart separates the Bone Valley into two units, an upper and lower. The upper unit, which averages about eight feet in thickness, is composed of sandy clay to clayey sand. The contact with the lower unit is gradational and generally includes a zone of soft white phosphate that was not economically recoverable. The mining companies considered all of these upper layers to be overburden. The lower unit contains most of the recoverable phosphate deposits. It averages about 10 feet in thickness and is composed of clayey sand or sandy clay. The average mined material consisted of roughly equal parts of recoverable phosphate, sand, and clay (Cathcart 1964). All of the above units are represented as the surficial aquifer or model layer one.

Underlying the Bone Valley Formation is the Hawthorn Formation, also divided into two units. The upper unit, consisting of olive-green micaceous clayey sand, is missing in most of the Saddle Creek Watershed (Cathcart 1964). The lower unit thickness varies from zero in the north to approximately 120 feet at southern end of the Lakeland 7.5" quadrangle (28 degrees, 0 minutes). The unit consists of impure limestone and dolomite, and grades upward to a residual calcareous clay. The calcareous clay contains phosphate sand and nodules. In general, the clayey layer contains less phosphate and more clay than does the lower Bone Valley Formation. Below the residual clay is the limestone or dolostone of the lower Hawthorn Formation. Phosphate mining generally stopped at this competent layer. As the Hawthorn thickens to the south, this limestone

46

Figure 30. Far-Field Model Leakance Between Layers 1 and 2.

47

Figure 31. Far-Field Model Leakance Between Layers 2 and 3.

48

Figure 32. Far-Field Model Layer 2 Transmissivity.

49

Figure 33. Far-Field Model Layer 3 Transmissivity.

50

Figure 34. Far-Field Model Layer 4 Transmissivity.

51

layer develops into the intermediate aquifer (layer 2 of the model); however, in most of the Saddle Creek area the limestone layer is too thin or discontinuous to form an effective aquifer. The calcareous clay of the Hawthorn forms a confining unit for the limestone layers below. Below the Hawthorn Formation are the Tampa, Suwannee, and Ocala Limestones. These three limestone units represent the upper Floridan aquifer, layer three in the model. Below the Ocala Limestone is the Avon Park Formation, the lower Floridan aquifer and model-layer 4. A large portion of the Saddle Creek Watershed has been extensively mined for its phosphate deposits. Much of the original stratigraphy, especially of the surficial aquifer system, has been substantially altered. Typical patterns of alteration are mine cut lakes, clay settling areas, clean sand tailings, and large tracts of reclaimed homogenized overburden. Some consequences of this mining activity are reduced infiltration in the clay settling areas, increased infiltration in sand tailings, and increased recharge where the confining layer has been reduced or breached. Historic Aquifer Data

The USGS monitors five wells in or near the USCW (Figure 35). Water levels for those wells for the past twenty years were obtained from the Orlando USGS office and entered into the model database. Three of the wells (Fish Lake, Tenoroc Road, and Lake Alfred) are Floridan wells. Two wells are located at Combee Road and State Road 33, one is a shallow well and the other is classified as intermediate but has water levels

Figure 35. Monitor Well Locations Near USCW.

52

substantially above those the intermediate would have if it existed at that location. This “intermediate” well is not used by the USGS in the creation of either the intermediate or Floridan potentiometric surface maps. The well probably represents a perched water table due to the extensive distribution of clays in the area, but the relative change in water level can still be instructive. Figures 36 through 40 contain the well hydrographs. As can be seen, except for possibly the surficial well, water levels appear to be generally increasing over the period of record. Because mining has ceased in the area, the increase in water levels may represent a rebound from depressed levels during the mining period. Note particularly Figure 40, the Tenoroc Mine Road observation well, which is the closest well with a long-term record to the Tenoroc site. Water levels have been slowly increasing since the late 1970's, which coincides with the cessation of mining at Tenoroc.

Figure 36. USGS Combee Road and State Road 33 Shallow Well.

53

Figure 37. USGS Combee and State Road 33 Intermediate Well.

Figure 38. USGS Lake Alfred Floridan Well.

54

Figure 39. USGS Fish Lake Floridan Well.

Figure 40. USGS Tenoroc Road Floridan Well.

55

Model Domain and Boundary Conditions

The selected domain was defined by a combination of large-scale model domain and near-field sub-basins. The Upper Saddle Creek Watershed was used to define the domain of the calibrated surface water model. This domain was extended by approximately one far-field groundwater cell to define the extent of the near-field grid. Basins. The Upper Saddle Creek watershed, USCW, was divided into 47 sub-basins. These basins were delineated from USGS 24,000 scale quads, available SWFWMD aerials with topography, and from field surveys. Even with a lack of current topography in the mined-out area in and around Tenoroc, basin boundaries were easily defined from field surveys (some during the unusually wet El Niño winter of 1997-98). The basin boundaries do not match the USGS basin delineations used in the far-field model calibration. The basin delineations and basin numbers are shown in Figure 41. The basin discharges were routed to streams or lakes (reaches). The routing information is shown in Table 5. Hydrography. Hydrography data were gathered from several sources: (1) digitized for the project from recent aerials, (2) SWFWMD land use mapping, and (3) USGS/EPA RF3 (McKay and others 1994) hydrography coverage. Spatial data from all sources were combined into one complete coverage of the basin. Attributes were added to the database for hydrologic modeling. The polygon data were distributed into 5 classes: MC (mine cut), OW (open water), FW (forested wetland), WL (wetland), LA (land). (The classification “land” is actually an island in a lake and is part of the basin, not the hydrography. Hydrologic attributes were assigned to the polygons using this classification. These attributes were used within the GIS to create the stage/area/volume relationships for the model rating (DAVD) tables. A similar technique was used for the streams. In the case of the stream hydrography the modified Strahler order was used in order to classify the reach. The order classification then defined the relative size of the reach, and therefore, the attributes used in the GIS analysis. The hydrography and classification used in the model are shown in Figure 42. The discharges were routed from one reach to the next down to the outfall. The reach-to-reach routing used in the model is shown in Table 6. Groundwater Grid. The near-field grid was established to provide a one grid-cell buffer from the far-field model around the surface water basins. This produced a grid of 7 by 8 cells at the northeastern side of the far-field model. To obtain a finer resolution, the cell length was reduced from two miles to one-quarter mile. The result was a 64-row

56

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Table 5. Near-Field Basin to Reach Routing.

Basin Reach Basin Reach 1 1 24 23 2 4 25 18 3 3 26 21 4 2 27 25 5 5 28 24 6 42 29 21 7 41 30 20 8 6 31 38 9 9 32 45 10 10 33 36 11 12 34 37 12 11 35 22 13 18 36 46 14 43 37 13 15 39 38 13 16 44 39 13 17 15 40 13 18 29 41 13 19 8 42 48 20 32 43 49 21 30 44 47 22 34 45 19 23 27 46 26

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Table 6. Near-Field Reach to Reach Routing.

Reach Reach Reach Reach 1 7 26 28 2 7 27 28 3 7 28 37 4 7 29 31 5 14 30 31 6 16 31 34 7 16 32 34 8 16 33 37 9 10 34 37 10 12 35 36 11 17 36 37 12 17 37 47 13 44 38 47 14 21 39 44 15 16 40 41 16 34 41 42 17 23 42 44 18 23 43 44 19 23 44 45 20 26 45 50 21 24 46 50 22 28 47 50 23 24 48 50 24 25 49 50 25 27

by 56 column grid with each grid cell one-quarter mile by one-quarter mile or one-sixteenth square mile (over 224 mi2). The USCW is completely contained within the grid (see Figure 43). The northern boundary of the near-field grid duplicates the no-flow boundary defined in the far-field model. The other boundaries of the near-field model are head-dependent boundaries with conductance values derived from the far-field model.

60

Figure 43. Near-Field Basins and Near-Field Grid Alignment. Hydrostratigraphy. To be consistent with the far-field model, the same hydrostratigraphy was used in the near-field model: four layers representing the surficial, intermediate, upper Floridan, and lower Floridan aquifers (shown previously in Figure 10).

61

In a large portion of the northern model domain, the intermediate aquifer does not exist or is discontinuous. To accommodate the absence of the intermediate aquifer in the northern model domain, the leakance between layer 2 and layer 3 was set to a high value (10 feet/day/foot) and transmissivity was set to zero where the intermediate aquifer is absent. The high leakance between layers 2 and 3 causes the downward flow from layer 1 to layer 3 to be controlled by the leakance value for layers 1 and 2. The zero transmissivity value insures that no lateral flow occurs in layer 2, thus any water moving downward from the surficial aquifer goes directly into the Floridan. Initial Conditions. The initial water-table elevations in the groundwater grid were established by interpolating between grid cells with known water-table elevations. Where a surficial well existed within a grid cell the measured water-table value at the beginning of October 1996 was used. For large lakes that covered multiple cells, the lake stage at the start of the simulation period was used as the water-table elevation. The initial aquifer elevation of the intermediate aquifer was interpolated from the September 1996 and the May 1997 USGS potentiometric surface maps. To define the initial heads for the Floridan aquifer, an ARC/INFO TIN (triangulated irregular network) was created using the beginning-of-October measured Floridan elevations on the Tenoroc property combined with the SWFWMD end-of-September Floridan monitoring well data. This TIN represents an interpolated surface for the Floridan aquifer through out the model domain. The initial Floridan head at each grid cell center was estimated by locating the center of the grid cell on the TIN surface. Meteorologic and Hydrologic Time Series Based on the design from preliminary investigation of available data, a continuous field data collection network was installed by the USGS and USF from which hydrologic and meteorologic data were collected for approximately 30 months. The data collection continued through the end of the third year of the project, six months longer than proposed to capture a post El Niño drying period. The network included seven continuous streamflow gaging stations, four periodic streamflow sites, 10 lake stage-gages (two continuous and eight periodic), two rainfall gages, a continuous Upper Floridan and a water-table monitor well, five periodic Floridan monitor wells, and five periodic surficial wells. Figures 44 through 46 show the Tenoroc Fish Management Area and the station locations. Another FIPR-funded and USGS-conducted data collection project was located north of Tenoroc on the Williams Company property. The data from the Williams property (Powers 1999) was made available for use in this project. This additional field data collected on Williams property included: two periodically monitored Upper Floridan and 15 water-table wells, two streamflow gages, and an additional rain gage. Bi-weekly field trips were made by USF personnel to record water levels in the surficial wells, water levels in Floridan wells, and lake stages. Also recorded were flows

62

in streams not monitored by the USGS. Field trips to the study site, by USGS personnel, were scheduled at approximate six-week intervals to perform general maintenance and servicing of the continuous recording data-collection network. Streamflow measurements were performed during all routine site visits and when special site trips were required, during periods of high-flow for stage-discharge rating. The supplemental field data collection continued at monthly intervals together with USGS data collection through March 1999. One additional rain gage was installed at Lake A (this gage was installed to replace the gage that was removed on the Williams property north of Tenoroc). Four more surficial wells were installed in Tenoroc to better measure the water table elevation spatial and temporal response. These wells were also surveyed vertically. The supplemental data collection consisted of a total of 10 surficial wells, one “intermediate” well, six Floridan wells, 10 lake stages, and six additional stream discharge locations. The supplemental field data collection was in addition to the data collection by the U.S. Geological Survey described earlier. Rainfall. Site specific rainfall was collected for this project (Figure 44). The rainfall collected by the USGS for this project at Station 17A and Station 542. These rain gages collected the rainfall quantity using a fifteen minute time step. Additional rain data were obtained from the NWS for Lakeland Station, recorded at fifteen minute intervals, and from another FIPR/USGS (Powers 1999) project on the Williams land north of Tenoroc, also collected at fifteen minute intervals. Additional rain data were also collected by USF. The Lake A gage was installed late in the project to replace the data from the Williams gage that was removed. The rainfall data utilized in the model were recorded and utilized in the model at fifteen minute intervals. Using a small time step for the input time series allows accurate determination of the rainfall intensity. If a particular gage had failed or recorded erroneous data then the next closest gage was used to fill the missing data. Thiessen polygons of the rain gage locations were created. The rainfall on a basin was the area weighted average (based on areas of the Thiessen polygon overlay) of all the gages that influenced the basin. Evapotranspiration. Pan evaporation was monitored by the USGS at the Eagle Lake station. These data were un-usable for modeling needs due to the large number of errant data points. Instead of using the data directly, a sinusoidal curve was fit to the data. The sine curve followed the general trend of the pan data, but formed a continuous function filling the voids caused be the missing and errant data. This pan evaporation data were used to estimate potential ET for the entire near-field domain. The data were utilized at a daily time step and stored in the WDM file for use in the simulation.

63

#

# #

#

WILLIAMS POND CLAY MONITOR WELL NR LAKELAND

Lakeland

TENOROC DITCH ABV STR (SITE 17A) NR LAKELAND, FL

SADDLE CREEK AT STATE HIGHWAY 542 NEAR LAKELAND, FL

4 0 4 8 Miles

N

EW

SSurface Water Basin

# Rainfall Station

Rainfall Thiessen Polygon

Figure 44. Near-Field Basins, Rain Gage Locations and Thiessen Polygons.

Streamflow/Baseflow Separation. Continuous streamflow measurements were

made at seven locations within and around the Tenoroc area. The stations were located to capture the three major conveyances of the basin: Western, Central, and Eastern Ditches (see Figure 45). These gages were installed, maintained and rated by the USGS as a subcontract to this project. All stations and all data collected at each station were used for calibration. Before the calibration process began, baseflow separation for each station was performed. The same baseflow separation technique as described for the far-field

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streamflow stations was employed for the near-field data collection stations. The length of the running average windows was determined to be 180 days. The sub-basins in the USCW model have large storage attenuation properties (many lakes and wetlands). This storage attenuation mandated the long averaging periods in order to capture the true minimum or baseflow condition and not a storage release flow. The extremely wet El Niño winter (1997-1998) also mandated the long window because of the very long storage release time frame in the observed hydrograph. Lake Stages. Lake stages were recorded manually during bi-weekly site visits performed by USF personnel. Staff gages were located in the major lakes within the Tenoroc Fish Management Area (Figure 46). The lakes gaged were 5, 4, 3, 2, B, C, D, Hydrilla, Picnic, and Derby. All lake gages were surveyed to NGVD (National Geodetic Vertical Datum) by either Pickett and Associate, BCI, or USF staff. Continuous lake stages were also available via the streamflow gages installed by the USGS. The discharges from Lake 5 and Lake 2 were monitored by the USGS by rating the stage recorded by data logger. Therefore, the stages of Lake 5 and Lake 2 were recorded continuously. These two USGS continuous gages were also surveyed to NGVD. See Figure 46 for location of lake staff gages.

Figure 46. Tenoroc Lake Staff Gages and Monitoring Well Locations.

66

Groundwater Data Collection. Monitoring wells were installed to collect groundwater elevation data. To avoid difficulties obtaining landowner approvals, better insure well security, and limit costs, a surficial monitoring network was installed on the Tenoroc property. While this arrangement provided good coverage of the Tenoroc area, it limited the availability of water-table data in much of the SCWA. To expand the water-table coverage, especially outside of the surface water domain, monthly lake-stage data for major lakes in the groundwater domain were obtained from SWFWMD (Table 7). Table 7. Monthly Lake Stages (in Feet NGVD) for Major Lakes in the Near-Field

Domain (Values Identified with an Asterisk [*] Are Estimated).

Date Gibson Parker Hollingsworth Juliana Arietta Ariana Lena HancockOct96 142.81 130.42 131.46 132.61 142.84 136.24 136.24 100.49 Nov96 142.49 130.48 131.44 132.82 142.98 136.24 136.24 100.49 Dec96 142.65 130.24 131.10 132.57 142.66 136.02 136.02 100.00 Jan97 142.65 130.42 131.16 132.52 142.82 136.26 136.26 100.00 Feb97 142.61 130.36 131.00 132.40 142.64 136.20 136.20 99.58 Mar97 142.43 130.20 130.86 132.27 142.52 136.16 136.16 99.40 Apr97 142.08 129.90 130.60 132.01 142.38 136.02 136.02 98.97 May97 142.54 129.96 130.94 132.09 142.32 136.06 136.06 99.00 Jun97 142.40 129.90 130.78 131.89 142.10 135.90 135.90 98.90 Jul97 142.78 130.05 131.29 131.97 142.30 136.12 136.12 98.60

Aug97 142.76 130.68 131.80 132.31 142.80 136.72 136.49 99.00 Sep97 142.50 130.38 131.42 132.20 142.84 136.18 136.54 98.95 Oct97 142.81 130.24 131.88 132.15 142.46 135.92 136.18 98.94 Nov97 142.87 130.72 132.32 132.21 142.40 136.04 135.92 98.99 Dec97 142.89 130.80 132.18 132.56 142.80 136.42 136.04 100.76 Jan98 143.5* 131.48 131.48 133.36 143.54 136.58 136.42 102.90 Feb98 143.4* 130.70 131.82 133.38 143.36 136.36 136.28 105.70 Mar98 143.4* 131.10 131.50 133.72 143.40 136.64 136.20 106.84 Apr98 143.3* 131.00 131.85 133.63 143.30 136.34 136.40 108.90 May98 142.6* 129.97 131.40 133.13 142.62 136.1* 136.06 108.46 Jun98 141.95 129.82 130.98 132.54 142.62 135.92 135.86 108.31 Jul98 141.61 129.40 131.00 132.08 142.04 135.36 135.92 107.60

Aug98 142.0* 130.22 131.45 132.14 142.12 135.78 135.36 107.30 Sep98 142.44 130.04 131.25 132.03 141.88 135.56 135.78 107.18 Oct98 142.5* 131.35 132.06 132.99 142.54 136.34 135.56 107.24 Nov98 142.2* 130.21 131.97 132.61 142.22 135.86 136.10 107.10 Dec98 142.2* 130.39 131.72 132.40 142.20 135.90 135.86 106.74 Jan99 142.0* 130.30 131.54 132.21 142.00 135.78 135.90 105.86 Feb99 142.0* 130.36 131.45 132.23 142.00 135.82 135.78 105.30 Mar99 141.7* 130.15 130.90 131.95 141.70 135.56 135.82 104.52

67

Sites were identified as representing both mined (S1, S3, and S4) and unmined areas (S2), for the installation of four surficial monitoring wells (Figure 46). A fifth existing surficial well in a mined area was included in the Tenoroc well network (S5). Data were also collected from a USGS surficial well at State Road 33 and Combee Road outside of the Tenoroc area but within the SCWA.

Five existing Floridan wells on the Tenoroc property (wells beginning with ‘F’)

and a USGS Floridan well on Tenoroc mine road (U2) supplied data for the Floridan aquifer. One surficial well (S4) was located adjacent to an existing Floridan well (F7). Both the Floridan and surficial well had continuous recording equipment installed to provide a time series of differential head values between the Floridan and the surficial aquifer. These values were used to estimate the vertical flow direction and magnitude between the surficial aquifer and the Floridan aquifer.

The USF geotechnical department was contracted to explore the Tenoroc stratigraphy using direct push technology (continuous coil cone penetrometer). This truck mounted cone penetrometer was used to catalogue the subsurface lithology at five sites (Figures 47-51). The penetrometer measures tip resistance as well as the skin or sleeve (side wall) resistance on the cone as it is pushed through the ground (to a maximum of 40 feet or to limestone, whichever came first). An estimate of the type of material through which it passes can be made using the ratio between the tip and skin resistance. Sandy soils have high tip resistance and low skin resistance, while cohesive soils, such as clayey soils, will have high skin resistance and low tip resistance. Sandy, silty, and clayey intervals were identified as well as the top of the limestone at most locations. An interesting observation from the cone penetrometer test in Tenoroc was that some unmined areas have thick clayey surficial soils which undoubtedly contributed to the area’s historic extensive wetland landforms. Four additional surficial wells were added toward the end of the project. One well (S7) was added in a mined area near the Collins cemetery well (S2) to validate the observed S2 water levels. Two other wells (S6 and S8) were added to mined areas, and one well (S9) was placed in an unmined area. These additional wells were located at the penetrometer test sites. Because these additional wells were added so late in the project, there were too few water-level measurements to justify their inclusion in the model.

Field trips to Tenoroc were made regularly by USF personnel to measure water

elevations during the study period. Figure 52 illustrates the measured water levels during the project. Because the groundwater data were limited to a small area of the Saddle Creek Watershed, additional calibration target data were estimated from SWFWMD records. SWFWMD maintains a series of Floridan aquifer monitoring wells from which data is collected monthly (no intermediate monitoring wells are located in the near-field model domain). Monthly Floridan elevations were obtained from SWFWMD for the simulation

68

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Figure 52. Aquifer Elevations Measured During the Study Period. period. These elevations were combined with the project Floridan well records and a TIN representing the Floridan potentiometric surface was created for each monthly time step.

Additional data were obtained from three engineering studies done at Tenoroc

during the project time period. Madrid (1998) evaluated two sites as possible locations for fly ash monofills. Site 1, at Lake D, was found to have a depth to limestone of approximately 30 feet. Site 2, just south of the Williams property at Combee road, had a depth to limestone of 30 to 40 feet. Chastain-Skillman, Inc., working on a sprayfield irrigation project for the city of Auburndale measured water-table elevations along the eastern boundary of Tenoroc near Lake Myrtle between 128 and 140 feet from 2/4/98 to 4/2/98. At a nearby site, the city of Auburndale Westside Wastewater treatment plant, Chastain-Skillman estimated hydraulic conductivity values from slug tests to be between 2 and 8 feet/day (personal communication).

Groundwater Pumping Records. To properly calibrate the FHM groundwater

component, groundwater withdrawal rates had to be determined. Using a well-head meter, SWFWMD collects pumping rate data from high-volume users. For permitted wells without meters, pumping rates are estimated. SWFWMD provided estimated and

74

metered pumping data for all the permitted wells in the model domain through 1997. For 1998 and 1999, only metered data were available. To estimate pumping data for 1998 and 1999, the ratio between 1997 withdrawals from estimated wells and metered wells was calculated. This ratio was then applied to the metered well data for 1998 and 1999 to arrive at estimated withdrawals for these wells. Thus, if a 50% pumping increase from metered wells resulted in a 35% pumping increase in estimated wells in 1997, that same factor was applied to unmetered wells in 1998 and 1999. Figure 53 details the locations of the metered and estimated wells.

Simulation Period. The simulation period for model calibration was defined by

the period that the near-field data were collected. In this case, the data were collected from August 1996 to March 1999. The calibration period included extended dry and extremely wet periods (including an El Niño abnormally wet winter rainfall). Including both extreme conditions in the calibration period helps boost confidence in the model’s predictive capability for a wide range of conditions. All available data were used for the calibration. No verification period is available due to the lack of observed data.

Surface Water Calibration

Surface water calibration was performed using the observed stream discharges,

stream stages, and lake stages (see data collection above). Through the baseflow separation process a chart of cumulative runoff and baseflow was produced from the observed data. The simulated data for all basins upstream of the gage were then accumulated into an area weighted average for comparison with the observed data. At first, this comparison was performed on the basin budget only. It did not include reach attenuation nor direct rainfall on the reaches. Absence of the reach analysis does not significantly affect the basin budget. Indeed, it was more important to isolate the basin simulation and attempt calibration of the basin parameters before attempting a full basin and reach simulation. With the basins calibrated, the reaches were added to the simulation and calibrated separately with little or no modification to the basin budget. The results shown below are actually the results of the integrated simulation. Figures 54-60 show the calibration results for the observed stations. Lake stages from the model were also compared to available field data. The HSPF model uses a relative stream depth within the simulation. The output depths are then converted to actual stages by adding a stage correction factor. To calibrate the lake stages, the reach stage-storage-discharge relationship (rating conditions contained in HSPF) were modified in order to obtain a good match to observed stages. Comparison of the calibrated lake stages are shown in Figures 61-66. Table 8 shows the calibrated basin parameters for all basins in the simulation. Basins that did not contribute to an observed stream gage (such as the lower basins that could not be measured because of the tail water effects from Lake Hancock) had basin parameters determined from either the far-field calibration or from other “hydrologically similar” basins in the near-field domain.

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Figure 53. Metered and Estimated Wells in the Near-Field Model Domain.

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Figure 54. Station 11 Calibration (Lake 5 Inflows from Basins 9-13, 45).

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Figure 55. Station 13 Calibration (Lake 5 Outfall into Lake 4, Including Basins

9-13, 24, 25).

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Figure 56. Station 17a Calibration (Lake 2 Outfall into Central Ditch, Includes

Basins 9-13, 23, 24, 27-29, 45).

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Figure 57. Station 17b Calibration, Downstream of Central and Eastern Con-

fluence, Basins 5, 9-13, 23-30, 35, 45.

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Figure 58. Station 19 Calibration, Eastern Ditch Before Tenoroc, Basins 5, 25.

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Figure 59. Station 20 Calibration, Western Ditch, SW Corner of Tenoroc, Basins

1-4, 8, 17-22.

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Figure 60. Station 542, Saddle Creek at 542, Basins 1-35, 44, 45.

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Figure 61. Lake Stage Calibration Comparison, Picnic Lake.

Figure 62. Lake Stage Calibration Comparison, Lake 3.

84

Figure 63. Lake Stage Calibration Comparison, Lake 4.

Figure 64. Lake Stage Calibration Comparison, Lake 2.

85

118.5

119

119.5

120

120.5

121

121.5 L

ak

e S

tag

e,

ft.

NV

GD

15-May-96 01-Dec-96 19-Jun-97 05-Jan-98 24-Jul-98 09-Feb-99 28-Aug-99 Date

Simulated Observed

Lake 5 (23)

Lake

Sta

ge, f

t. N

GVD

Figure 65. Lake Stage Calibration Comparison, Lake 5.

Figure 66. Lake Stage Calibration Comparison, Lake Hydrilla.

Table 8. Calibrated Near-Field Subbasin Parameters.

Basin # FOREST INFILT LSUR SLSUR INFEXP INFILD UZSN NSUR LZS 1 1 0.100 200.0 0.0020 4.600 1.200 0.050 0.1500 12.880 2 2 0.020 300.0 0.0030 4.600 1.200 0.050 0.1500 26.130 3 3 0.020 100.0 0.0030 4.600 1.200 0.100 0.3000 19.780 4 4 0.020 100.0 0.0030 4.600 1.200 0.100 0.2000 17.870 5 5 0.100 200.0 0.0060 4.600 1.200 0.050 0.1500 18.710 6 6 0.080 355.0 0.0030 4.600 1.200 0.100 0.1000 31.460 7 7 0.150 224.0 0.0045 4.600 1.200 0.120 0.1500 16.350 8 8 0.080 200.0 0.0050 4.600 1.200 0.050 0.1500 7.520 9 9 0.020 100.0 0.0060 4.600 1.200 0.120 0.3000 42.740 10 10 0.020 100.0 0.0060 4.600 1.200 0.120 0.3000 28.850 11 11 0.020 88.0 0.0300 4.600 1.200 0.120 0.3000 24.070 12 12 0.020 200.0 0.0040 4.600 1.200 0.120 0.2000 15.440 13 13 0.150 148.0 0.0030 4.600 1.200 0.080 0.1500 5.990 14 14 0.100 377.0 0.0030 4.600 1.200 0.100 0.1000 71.800 15 15 0.150 200.0 0.0030 4.600 1.200 0.120 0.2000 7.160 16 16 0.030 155.0 0.0027 4.600 1.200 0.050 0.1000 22.780 17 17 0.150 230.0 0.0030 4.600 1.200 0.050 0.1500 6.520 18 18 0.150 196.0 0.0012 4.600 1.200 0.100 0.2000 8.140 19 19 0.020 162.0 0.0050 4.600 1.200 0.100 0.2000 52.070 20 20 0.150 347.0 0.0030 4.600 1.200 0.050 0.1500 9.110 21 21 0.150 227.0 0.0030 4.600 1.200 0.050 0.1500 9.460 22 22 0.150 163.0 0.0027 4.600 1.200 0.120 0.2000 14.870 23 23 0.150 181.0 0.0050 4.600 1.200 0.050 0.2000 8.250 24 24 0.100 164.0 0.0060 4.600 1.200 0.050 0.1500 6.530

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Table 8 (Cont.). Calibrated Near-Field Subbasin Parameters.

Basin # LZSN INFILT LSUR SLSUR INFEXP INFILD UZSN NSUR LZS 25 9.700 0.100 227.0 0.0030 4.600 1.200 0.050 0.1500 5.680 26 28.900 0.150 250.0 0.0032 4.600 1.200 0.050 0.1500 22.160 27 19.000 0.150 80.0 0.0100 4.600 1.200 0.120 0.1500 2.760 28 19.000 0.150 80.0 0.0100 4.600 1.200 0.050 0.1500 7.830 29 7.200 0.100 152.0 0.0030 4.600 1.200 0.120 0.2000 7.090 30 16.500 0.150 306.0 0.0035 4.600 1.200 0.120 0.2000 19.800 31 14.400 0.150 253.0 0.0018 4.600 1.200 0.120 0.2000 9.430 32 16.800 0.150 328.0 0.0015 4.600 1.200 0.120 0.2000 10.950 33 10.000 0.020 257.0 0.0030 4.600 1.200 0.100 0.1000 23.770 34 7.200 0.020 100.0 0.0040 4.600 1.200 0.120 0.3000 9.050 35 1.000 0.010 100.0 0.0040 4.600 1.200 0.120 0.2000 8.580 36 10.700 0.110 186.0 0.0030 4.600 1.200 0.100 0.2000 13.790 37 29.500 0.150 283.0 0.0065 4.600 1.200 0.120 0.2000 18.020 38 32.900 0.150 225.0 0.0029 4.600 1.200 0.120 0.2000 13.520 39 12.900 0.150 262.0 0.0034 4.600 1.200 0.120 0.2000 7.770 40 12.200 0.150 232.0 0.0021 4.600 1.200 0.120 0.2000 11.930 41 14.900 0.150 222.0 0.0027 4.600 1.200 0.120 0.2000 12.070 42 9.600 0.150 387.0 0.0032 4.600 1.200 0.120 0.2000 9.430 43 7.200 0.150 296.0 0.0018 4.600 1.200 0.120 0.2000 10.850 44 19.200 0.100 205.0 0.0056 4.600 1.200 0.120 0.2000 10.450 45 9.600 0.100 339.0 0.0040 4.600 1.200 0.080 0.2000 18.390 46 16.590 0.150 283.0 0.0049 4.600 1.200 0.220 0.2000 13.390 47 16.590 0.150 283.0 0.0049 4.600 1.200 0.220 0.2000 17.510

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Groundwater Calibration Groundwater models generally provide more robust predicted values when the

number of parameters is minimized and the distribution of parameters is simplified. The system should not be excessively parameterized when there is insufficient field data to support it. To this end, it was desired to achieve a good fit of simulated heads to observed heads while minimizing the number and complexity of parameter zones.

At the scale of the groundwater model, most of the groundwater flow in the surficial aquifer is downward, therefore sensitivity to layer 1 hydraulic conductivity is minimized. SWFWMD used hydraulic conductivity values between 1 and 40 ft/day in the district-wide model domain (Ross and others 1997) and values of 8 to 12 ft/day throughout most of the near-field model area. A study by Chastain Skillman Inc. (Tenoroc Reuse Project, City of Auburndale effluent disposal site, personal communication) reported hydraulic conductivity values determined by slug tests of between 2 and 8 ft/day at an unmined adjacent site. Because hydraulic conductivities derived from slug tests can be questionable and the radius of influence of slug tests is very small, a hydraulic conductivity value of 10 ft/day was used in the model for all of layer 1. This value represents the midpoint of the 8 to 12 ft/day used by SWFWMD and is consistent with the upper range of the slug test values.

Vertical movement of groundwater in the model is controlled by the leakance

value. The model (similar to the actual system) is very sensitive to leakance. Floridan wells in the domain were particularly sensitive to leakance between layers 1 and 2 as were surficial wells S1, S3, and S5, and to a lesser extent, surficial wells S2 and S4. Surficial well S10 was not very sensitive to any parameter.

Two distributions of leakance were identified by mapping head differences (head residuals) between simulated and interpolated heads. Areas with similar patterns of head residuals were incorporated into leakance zones. The leakance values for the zones were optimized with PEST. Adjacent zones with similar optimized leakance values were combined. The final results were the three leakance zones in layer 1 shown in Figure 67.

Because the near-field groundwater model was run in transient mode (not steady

state), two aquifer storage terms needed to be defined: specific yield (dimensionless) for the unconfined aquifer, and specific storage (dimension: 1/length) for the confined aquifer. Several different physically based specific yield distributions were optimized using PEST. The most promising distributions were based on soil maps and Department of Environmental Protection internal mining land use codes. The best-fit distribution for specific yield with the least complexity was 0.2 for unmined land and 0.04 for mined-out land (DEP. code MOA), illustrated in Figure 68. The specific storage was set to 10-5 /ft, a typical value for a limestone aquifer characterized by layers 2-4.

The leakance values between layers 2 and 3, and layers 3 and 4, and initial

transmissivity values for layers 2, 3, and 4 were retained from the far-field model. The transmissivity distribution for layers 3 and 4 was later altered slightly during optimization

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Figure 67. Near-Field Leakance Distribution (Ft./Day/Ft.).

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Figure 68. Near-Field Layer 1 Specific Yield Distribution.

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(see Figure 69). The transmissivity distribution for layer 4 is the same as for layer 3, although the values are four times greater.

One valuable source of data for calibration of the groundwater elevations was water measurements made during the project period. To augment water elevation data, estimates of the Floridan aquifer water levels at locations scattered throughout the SCW derived from the potentiometric surface TINs were used (see Figure 70). Hydrographs for the surficial and Floridan wells for both the measured and simulated heads for the groundwater model are in Figures 71 and 72. Figure 73 shows contours of simulated heads compared with contours from the potentiometric TINs. These contours represent the final month of the simulation when the divergence between the simulated and observed data would be expected to be the greatest. The greatest difference between the observed contours and the simulated contours is at the west-central edge of the surface water basins where there is a cluster of metered wells (specifically the grid cells in row 30, column 11; row 31, column 10; and row 32 columns 8; 9; and 10). This is an area of substantial pumping (see Figure 53, Metered and Estimated Wells) with average rates over the project period of 4.6 mgd in the cell defined by row 31 column 10 and similar rates in the other cells. Because Floridan aquifer monitoring wells in that area are not used for the potentiometric maps of either SWFWMD or the USGS, the maps are not sensitive to water-level depression in that area.

Integrated FHM Calibration

Integrated calibration involved only minor adjustments to the individual surface water and groundwater pre-calibrations. Integrated model calibration followed pre-calibration of the individual surface water (HSPF) and groundwater components (MODFLOW). This constrains the number of parameter adjustments to a manageable level. If the system being simulated is strongly influenced by surface water and groundwater interactions, considerable calibration will be required during the integrated simulations. The results shown above (surface water calibration and groundwater calibration) depict the calibrated results of the FHM integrated model. The separate simulation of the surface water and groundwater components yield very similar results due to the calibration technique described earlier.

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Figure 69. Near-Field Layer 3 Transmissivity Distribution.

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Figure 70. Locations of Estimated Water Levels.

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Figure 71. Observed and Simulated Surficial Wells.

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Figure 72. Observed and Simulated Floridan Wells.

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Figure 73. Simulated and Observed Potentiometric Surface Contours.

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ALTERNATIVE OR PREDICTIVE SIMULATIONS Predictive scenarios were developed for possible basin and reach modifications that could improve the hydro-period of the Tenoroc Fish Management Area lakes and/or enhance existing wetlands or allow the creation of new wetlands. These alternatives, described below, included reach and basin modifications from proposed developments outside of Tenoroc or possible hydrologic modifications within Tenoroc. Each alternative has a brief narrative describing the modifications and a description of model modifications followed by graphics describing the effect the alternative has on lake levels and reach flows. All alternative simulations use the calibration background and meteorologic data and are presented in comparison with the calibration results that represent the existing conditions. Some of the alternatives utilize basins that were either not calibrated or only calibrated in aggregate with other basins. Due to the lack of individual calibration for these basins, exact quantities are difficult to defend. All basins and reaches affected by the alternative analyses were calibrated individually or at least in aggregate with other basins. Results are shown for only the calibrated stream gages affected by the scenario. The outfall of Reach 37, Saddle Creek at Saddle Creek Road (an uncalibrated station) was also included to represent the simulated impacts on the system at that point. ALTERNATIVE 1 - REDIRECT NORTHWEST WILLIAMS TO TENOROC EASTERN DITCH For this alternative, discharge from the Northwest Williams parcel would be routed into the Eastern Ditch (Figure 74). The Northwest Williams parcel currently flows to the Western Ditch. The Western Ditch basically by-passes all of Tenoroc. The runoff from the Northwest parcel of the Williams tract could be captured if the upper Western Ditch is blocked and redirected to the Eastern Ditch. Once in the Eastern Ditch, the water will flow to the central lake system via the Blue Hole station. The model was modified by simply changing the reach-to-reach routing in the simulation. Reach 7 is routed to Reach 5 instead of Reach 16 (see reach map, Figure 42, for classification). Comparison of the results with the background simulation are shown in Figures 75 to 80. Shown in the results is an increase in flows in the Central Ditch and a decrease in flows in the Western Ditch. The combined results (at Saddle Creek Road) described as Reach 37 show little effect because the re-routed water still makes it to the final outfall (just routed through the lakes). The storage attenuation caused by the lakes did reduce the peaks slightly while increasing the recession time of the hydrographs. The stages of Reach 5 were increased due to the added inflows (which should be a concern for local flooding and high tailwater conditions causing flow reversal). Further storage attenuation could be achieved by modifying the outfall of Lake 2 or the construction of additional wetlands or lakes.

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Figure 75. Discharge Comparison for Alternative 1 at Station 17a.

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Figure 76. Discharge Comparison for Alternative 1 at Station 17b.

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Figure 77. Discharge Comparison for Alternative 1 at Station 19.

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Figure 78. Discharge Comparison for Alternative 1 at Station 20.

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Figure 79. Discharge Comparison for Alternative 1 at Reach 37.

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Figure 80. Stage Comparison for Alternative 1 at Reaches 5 and 37. ALTERNATIVE 2 - REDIRECT SOUTHWEST WILLIAMS TO WESTERN DITCH Currently Northwest Williams discharges to the Western Ditch by-passing Tenoroc while the Southwest Williams discharges to the central Ditch into Lake 5. This alternative re-routes the discharge from Southwest Williams through the Northwest Williams into the Western Ditch (Figure 81), an alternative proposed by Williams reclamation engineers. This alternative would force the entire western half of the Williams tract to the Western Ditch, therefore by-passing most of Tenoroc. This alternative was simulated by routing the discharge from Reach 10 to Reach 3 instead of Reach 12.

As can be inferred, the Central Ditch at Station 11 saw a reduction in discharge. Almost 50% of the cumulative discharges was simulated from the Southwest Williams tract. Because of this reduction at Station 11, Station 13 simulated cumulative discharge was reduced by about 25% and Station 17a showed a reduction of about 15% in the cumulative discharge. This reduction of runoff at 17a was compensated by an increase at Station 20 (the Western Ditch). Station 20 simulated discharges were 20% greater than the background simulation. Because both Western and Central Ditches discharge to the Saddle Creek at the Saddle Creek Road there was almost no change in discharge at this

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station. This alternative reduced the peak stages of Reaches 17 and 23 (Lake 5), baseflow or low flow stages were unaltered. See Figures 82 to 86 for graphical comparisons between this alternative and the background simulation. ALTERNATIVE 3 - ROUTE BOTH NORTHWEST AND SOUTHWEST WILLIAMS TO EASTERN DITCH This alternative combines the previous two scenarios. Discharge from both Northwest and Southwest Williams parcels are routed into the Eastern Ditch. Southwest Williams is routed through the Northwest Williams tract while the northern part of the Western Ditch is re-routed to the Eastern Ditch. This was simulated by altering the routing of discharge from Reaches 7 and 10. Reach 7 (northern extent of the Western Ditch) is routed to Reach 5 (northern extent of the Eastern Ditch) instead of Reach 16. Reach 10 (ditch from Southwest Williams) is routed to Reach 3 (ditch from Northwest Williams) instead of Reach 12 (Figure 87).

This alternative resulted in an increase in discharges at Stations 11, 13, 17a, 17b and 19. These stations represent the Central and Eastern Ditches. Just as in Scenario 2 these increases in discharges are offset by a reduction in discharges at Station 20 (Western Ditch). The Western Ditch cumulative discharge was reduced by approximately 60%. Due to the added storage attenuation of the central fishing lakes (Lakes 5, 4, 3, and 2), the peaks were reduced while the recession limbs of the hydrographs were increased at the Saddle Creek Road. The cumulative discharge at Saddle Creek Road remains similar to the background simulation (see Figures 88 to 96). Reach stages were similarly affected. The stage in Reach 5 would be measured from the background levels by up to 2 feet. Reach 17 stages were reduced by almost the same amount. Some peak stages were reduced in Lake 5 (Reach 23), while stages at Saddle Creek Road (Reach 37) were affected by slightly reducing the peak stages while slightly increasing recessional stages (see Figures 96 and 97).

ALTERNATIVE 4 - ROUTE BOTH NORTHWEST AND SOUTHWEST WILLIAMS TO CENTRAL DITCH

This alternative reroutes both Northwest and Southwest Williams to the Central Ditch. Discharge from both Northwest and Southwest Williams parcels is routed (just as in scenario 3) to the northern extent of the Eastern Ditch (Reach 5, a lake in the northeast corner of Williams tract). This lake is then directed to discharge in the Central Ditch. This alternative is simulated in the model by routing Reach 10 into Reach 3 causing the Southeast Williams to discharge into the upper portion of the Western Ditch through Reach 3. Reach 7 is routed to Reach 5 instead of Reach 16, causing both the Northwest and Southwest Williams to discharge to Reach 5, a lake at the head waters of the Eastern Ditch. Discharge from Reach 5 is then routed to Reach 18 from Reach 14. The basin around Reach 5 (Basin 5) is then split 50%/50% between Reaches 5 and 14. The splitting

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Figure 82. Discharge Comparison for Alternative 2 at Station 11.

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Figure 83. Discharge Comparison for Alternative 2 at Station 13.

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Figure 84. Discharge Comparison for Alternative 2 at Station 17a.

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Figure 85. Discharge Comparison for Alternative 2 at Station 17b.

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Figure 86. Stage Comparison for Alternative 2 at Reaches 17, 23, and 37.

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Figure 88. Discharge Comparison for Alternative 3 at Station 11.

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Figure 89. Discharge Comparison for Alternative 3 at Station 13.

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Figure 90. Discharge Comparison for Alternative 3 at Station 17a.

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Figure 91. Discharge Comparison for Alternative 3 at Station 17b.

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Figure 92. Discharge Comparison for Alternative 3 at Station 19.

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Figure 93. Discharge Comparison for Alternative 3 at Station 20.

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Figure 94. Discharge Comparison for Alternative 3 at Reach 37.

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Figure 95. Stage Comparison for Alternative 3 at Reaches 5 and 17.

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Figure 96. Stage Comparison for Alternative 3 at Reaches 23 and 37.

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of the basin flows to the two reaches allowed simulation of this scenario without introducing the complications of adding another basin (Figure 97).

This alternative involved no basin parameter adjustments. This alternative would affect the water budget at Saddle Creek Road (Central Ditch) primarily from to changes in storage attenuation. At Station 11, the effects were very noticeable. Overall discharges increased by 150%. At Station 13, discharge was increased by 100%. An increase of 50% was simulated at Station 17a and 40% at Station 17b. The effect of the alternative on the system is reduced progressively downstream due to the increased contribution from additional unmodified basins. Station 19 on the Western Ditch showed a reduction of approximately 40%. Saddle Creek Road showed little change in total discharge over the simulation period. There were, however, minor changes in daily average flows resulting in slightly reduced peaks and longer recessions. Reaches 5 and 18 stages changed by almost 2 feet with an average increase of approximately one foot. The stages for Reach 23, or Lake 5, increased by almost one foot during the peak with an average increase of approximately 0.5 feet. Very little stage differences were noted at Saddle Creek Road. Again this reach had slightly lower peaks and higher recessional stages due to the added attenuation. See Figures 98 to 105 for comparisons between this alternative and the background conditions.

ALTERNATIVE 5 - SIMULATE EASTERN WILLIAMS WITH IMPERVIOUS AREA This alternative predicts the hydrology after the Eastern Williams tract is developed, implementing possible changes associated with a proposed DRI for this tract. Area and storage volume of surface water features in Williams Eastern Tract were assumed to be reduced by 30% and the reduced area was added to the basin area which represents filling of the lakes that presently exist. Of the modified land area, 30% was considered as impervious (paved landform) which represents an average impervious ratio of the proposed development. The surface area, storage volume, and initial storage of Reaches 1, 5, and 18 have been reduced by the prescribed 30%. The area reduction for Reaches 1, 5, and 18 has been added to the area of Basins 1, 5, and 13, respectively. Of the modified basin area, 30% is simulated as impervious by using the following PERLND parameters: short hydraulic length (SLSUR): 50 feet, lower overland friction (NSUR): 0.03, and lower infiltration index (INFILT): 0.01 in/hr. A new basin (48) has been created to simulate the combined imperviousness in each basin. Discharge from Basin 48 is routed to Reaches 1, 5, and 18 based on the percentage of the total impervious area of Basins 1, 5, and 13, respectively. The hydraulic lengths of Basins 1, 5, and 13, representing the pervious fraction, have been reduced by 50 feet. All other basin parameters were left unchanged (Figure 106).

The imperviousness simulated in the identified basins would produce more runoff. Also, the reduced reach storage would reduce basin discharge attenuation (therefore increasing peak discharges). At Station 11 (inflow to Lake 5), the alternative simulation predicted a 7% increase in cumulative discharge. Daily discharge peaks were increased from approximately 30 cfs to 35 cfs. The discharge increases occurred as a

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Figure 98. Discharge Comparison for Alternative 4 at Station 11.

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Figure 99. Discharge Comparison for Alternative 4 at Station 13.

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Figure 100. Discharge Comparison for Alternative 4 at Station 17a.

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Figure 101. Discharge Comparison for Alternative 4 at Station 17b.

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Figure 102. Discharge Comparison for Alternative 4 at Station 19.

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Figure 103. Discharge Comparison for Alternative 4 at Reach 37.

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Figure 104. Stage Comparison for Alternative 4 at Reaches 5 and 18.

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Figure 105. Stage Comparison for Alternative 4 at Reaches 23 and 37.

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direct response to the rainfall events. Station 19, the upper most station along the Eastern Ditch, had an increase of approximately 45% in the cumulative discharge (from 30 inches to 45 inches over the simulation period). Storm discharge peaks (daily averages) increased from 10 to 15 cfs to a simulated 15 to 20 cfs. Station 20 on the lower Western Ditch had an increase of 20% in the cumulative discharges over the simulation period caused by increases in daily average streamflow of 5 to 15 cfs. This alternative added 11% to the cumulative discharge as Saddle Creek Road (see Figures 107 to 110). Only minor changes were made to the reach stages; see Figures 111 and 112.

ALTERNATIVE 6 - REROUTE WESTERN DITCH TO SHOP LAKE THEN SHOP LAKE TO LAKE 2 This alternative was designed to investigate re-routing the discharge from Western Ditch, combined with Lakes G and F, into Shop Lake. Shop Lake is then rerouted to Lake 2. This alternative is simulated by effecting the reach routing within the model. In order to perform the modifications reaches have been aggregated. Reaches 24, 25, and 27 were aggregated into a modified Reach 27. Reaches 30, 31, and 32 were aggregated into a modified Reach 30. Due to aggregation, reach numbers have been altered (24 and 25 to 27 and 31 and 32 to 30) in the RIVER package of MODFLOW. The depth-discharge relationship was altered for Reach 30 due to the change in the discharge point of that reach. Discharge from Basins 23, 27, and 28 was routed to Reach 27 and discharge from Basins 20 and 21 was routed to Reach 30. Finally, discharge from Reach 30 (representing the combined Lake F, Lake G, and Shop Lake) flow was routed to Reach 27 or Lake 2 (Figure 113). The results of this alternative as compared to the background simulation are shown in Figures 114 to 118. Cumulative discharges at Station 17a were increased by 60% from the background simulation. A similar increase was shown at Station 17b, just downstream of 17a. Station 20 had a dramatic reduction in cumulative discharge; only 6% of the original flows made it to the gage. In effect, most of the flows can be captured and redirected to Lake 2. If the stage discharge relationship where to be modified for Lake 2, this water could be stored for longer periods allowing for increased low-flow conditions. The effect this alternative has at Saddle Creek Road is a decrease of less than 4% on the cumulative discharges. The peaks were reduced by almost 40 cfs, but the recession flows increased by almost 20 cfs. As discussed earlier, if the stage storage discharge of Lake 2 were modified (outlet structure changes), larger reduction in peaks and longer recession could be achieved. Reach stages were also modified with this alternative (see Figure 114). The stage in Reach 27 increased slightly throughout the simulation. Reach 30 had a significant increase due to the reach aggregation, but the overall change to stages through the basin modifications included longer time bases to the hydrographs and longer recession limbs. Reach 37, Saddle Creek at Saddle Creek Road, was modified only slightly. Obviously, more work is required to determine the size of the connection from Shop Lake to Lake 2 and whether the head gradient is such to allow flow from Shop Lake to Lake 2.

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Figure 107. Discharge Comparison for Alternative 5 at Station 11.

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Figure 108. Discharge Comparison for Alternative 5 at Station 19.

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Figure 109. Discharge Comparison for Alternative 5 at Station 20.

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Figure 110. Discharge Comparison for Alternative 5 at Reach 37.

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Figure 111. Stage Comparison for Alternative 5 at Reaches 1 and 5.

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Figure 112. Stage Comparison for Alternative 5 at Reaches 18 and 37.

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Figure 114. Discharge Comparison for Alternative 6 at Station 17a.

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Figure 115. Discharge Comparison for Alternative 6 at Station 17b.

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Figure 116. Discharge Comparison for Alternative 6 at Station 20.

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Figure 117. Discharge Comparison for Alternative 6 at Reach 37.

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Figure 118. Stage Comparison for Alternative 6 at Reaches 27, 30, and 37.

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ALTERNATIVE 7 – ADDITION OF CITY OF AUBURNDALE WWTP TREATED WASTE WATER

The City of Auburndale is progressing with the construction of a spray field to

discharge treated effluent adjacent to the Tenoroc Fish Management Area (Figure 119). This alternative sought to investigate the effects of this added inflow to the basin budget. To simplify the alternative analysis, the discharge was added directly to the Eastern Ditch system (in reality much of this water would be lost to ET). Discharge from the Auburndale WWTP was routed into the Eastern Ditch, Reach 21 for this alternative. The discharge rate was assumed to be a constant 2 mgd (3.1 cfs). Even though the effluent was added to the Eastern Ditch, the model routes this flow to the Central Ditch. This routing was done because of the discovery of a plug in the southern portion of the Eastern Ditch. This plug causes the water to back up and discharge through the mined area Lake 6, or New Area 4. This causes the flow in the upper Eastern Ditch to flow to the Central Ditch through the Lakes 4, 3, and 2 instead of continuing to the Central Ditch after the lakes. This plugged routing causes the Eastern Ditch to be attenuated through the lakes.

The results of this alternative are shown in Figures 120 to 124. The cumulative

discharge at Station 17a was increased by 27%. The increase was more noticeable during the recession limbs of the hydrographs. The increase was also significant at Station 17b and Saddle Creek Road, with 21% and 13% increases respectively. The increased inflow to the Lakes 4, 3, and 2 did little to modify the stages during high flow conditions but did increase the stages during low flow or dry conditions. This alternative overestimated the effects of the added treated water. Most of the water applied to a spray field will evaporate, with a small component going to baseflow. More analysis is required to obtain accurate alternative results.

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Figure 120. Discharge Comparison for Alternative 7 at Station 17a.

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Figure 121. Discharge Comparison for Alternative 7 at Station 17b.

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Figure 122. Discharge Comparison for Alternative 7 at Reach 37.

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Figure 123. Stage Comparison for Alternative 7 at Reaches 24 and 25.

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Figure 124. Stage Comparison for Alternative 7 at Reaches 27 and 37.

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FLOOD PROFILE SIMULATIONS INTRODUCTION To evaluate the potential levels of flooding within the Saddle Creek watershed during the 25- and 100-year design storm events, a hydraulic (backwater) model was developed for the primary channel system from Saddle Creek Road to State Road 540 just north of Lake Hancock (see Figure 125). The peak flows generated by the near-field surface water hydrologic model were input to the Saddle Creek hydraulic model to simulate the surface water profiles and flood profiles for the system. This resulted in frictional calibration for the model. The model was intended to be calibrated (and verified if possible) to support future as yet unidentified alternative wetland mitigation strategies that could be plausible and advanced for further study.

Figure 125. Saddle Creek Hydraulic Model Cross-Section Locations. MODEL BACKGROUND--HEC RAS The computer program HEC-RAS (HEC-RAS 1998a,b) was used in the analysis to simulate the water surface profiles in the Saddle Creek channel network. HEC-RAS was developed by the U.S. Army Corps of Engineers Hydrologic Engineering Center and is designed to calculate water surface profiles for steady, gradually varied flow in natural

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or man-made channels. The basic computational procedure used is based on the solution of the one-dimensional energy equation generally known as the Standard Step Method. The Standard Step Method is based on the energy equation with losses due to friction evaluated with the Manning's equation. The energy losses of channel expansion and contraction, and the effects of flow obstructions such as bridges, culverts, weirs, embankments, dams, channel improvements, and other structures in the floodplain, can be considered in the computations. The momentum equation was utilized in situations where the water surface profile is rapidly varied. These situations include mixed flow regime calculations (i.e., hydraulic jumps) and the hydraulics of bridges. The input data required for the model to perform backwater computations include: flow regime (flow at each cross-section), loss coefficients for structures, cross-section geometry for channels and structures, Manning's n, and reach lengths. More detailed data are required at crossings (bridge or culverts) to describe the section at which low flow, pressure flow (e.g., through culverts) or pressure and weir flow (e.g., flow through culverts and over top the roadway) could occur under various flow conditions.

The HEC-RAS program has a wide variety of output options including detailed information at each cross-section, cross-section geometry plots, water surface profiles, and summary tables for which the variables desired are user-defined. MODEL CONCEPTUALIZATION Reach Definition The hydraulic model for the Saddle Creek watershed was divided into the following reaches:

• Main Reach - From approximately 1200 feet upstream of Saddle Creek Road southward to the point where the creek splits into a primary channel and a secondary channel.

• Borrow Reach - Starting at the above mentioned fork, this reach consisted of the primary channel. This channel runs west then south where it connects with a large borrow pit area. The borrow pit area, in turn, discharges from its southern end. This channel, in turn, discharges into a larger channel located just north of Saddle Creek Park.

• Secondary Reach - Starting at the previously mentioned fork, this reach consisted of the secondary channel. The secondary channel runs parallel to the borrow pit area and discharges into the larger primary channel just north of Saddle Creek Park.

• Main 1 - Main channel located just north of Saddle Creek Park to the State Road 540 box culvert at Lake Hancock.

The location of the reach segments are shown in Figure 125.

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Channel Cross-Sections The basic input data required to develop the hydraulic model of the Saddle Creek channel system included the cross-section data for the channels and other more detailed data which describe the structure crossings such as bridges and culverts. These data were obtained from these sources:

(1) Polk County Parkway Authority-Parkway Bridge Construction Drawings (2) Bridge Division of the Florida State Road Department - Plan and Elevation

drawings for the SR 92 and CR 542 bridges. (3) Tampa office of the Florida State Road Department - Bridge Inspection

reports for the CR 540 culvert.

Main channel geometry was developed from field surveys taken at various locations along Saddle Creek. A total of 21 cross-sections were surveyed. In addition to the surveyed cross-sections, numerous interpolated cross-sections were added to the model in order to provide computational stability. In general, the added cross-sections were derived assuming prismatic sections interpolated between measured cross-sections. Information for the floodplain portion of both the field survey and dummy cross-sections was derived from 1 to 200 aerial maps of the area. Cross-section geometry for the field cross-sections is presented in the Appendix.

Structures There are six bridges and two roadway crossings with culverts in the Saddle Creek channel system which required the development of detailed information for model application. HEC-RAS computes energy losses caused by structures such as bridges and culverts in three parts. One part consists of losses that occur in the reach immediately downstream from the structure, where an expansion of flow generally takes place. The second part is the losses at the structure itself which can be modeled with several different methods. The third part consists of losses that occur in the reach immediately upstream of the structure, where the flow is generally contracting to get through the opening. To compute these energy losses, the bridge routines utilize four user-defined cross-sections. During the hydraulic computations, the program automatically formulates two additional cross-sections inside the bridge structure. In accordance to the guidelines presented in the HEC-RAS Hydraulic Reference Manual, the first user-defined cross-section was located sufficiently downstream from the structure so that the flow is not affected by the structure (i.e., the flow has fully expanded). Where feasible, the location of the downstream cross-section was based on USGS established criteria for locating this cross-section a distance downstream from the bridge equal to one times the bridge opening width. A second user-defined cross-section was located a short distance downstream from the bridge. As described in the HEC-RAS User’s Manual, this cross-section represents the effective flow area just outside the bridge. As described in the HEC-RAS User’s Manual, the distance between this cross-section and the bridge reflects the length

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required for the abrupt acceleration and contraction of the flow that occurs in the immediate area of the opening. The third cross-section represents the effective flow area just upstream of the bridge. Both the second and third cross-sections have ineffective flow areas to either side of the bridge opening during low flow and pressure flow profiles. In order to model only the effective flow areas at these two sections, the ineffective flow area option is selected at both of these cross-sections. The ineffective flow area was set at stations in an effort to adequately describe the active flow area at Cross-Sections 2 and 3. Where feasible, these stations were placed outside the edges of the bridge opening to allow for the contraction and expansion of flow that occurs in the immediate vicinity of the bridge. On the upstream side of the bridge, the flow is contracting rapidly. In accordance with the guidelines described in the HEC-RAS User’s Manual, the stations of the ineffective flow areas is to assume a 1:1 contraction rate in the immediate vicinity of the bridge. On the downstream side of the bridge, ineffective flow areas were set at stations equal to the width of the bridge opening or wider (to account for flow expanding). The fourth cross-section is an upstream cross-section where the flow lines are approximately parallel and the cross-section is fully effective. Cross-section placement was based on a USGS-established criterion for locating this cross-section a distance upstream from the bridge equal to the bridge opening width. During the hydraulic computations, the program automatically formulates two additional cross-sections inside of the bridge structure, one at the upstream and one at the downstream side of the bridge. The geometry of these formulated cross-sections is a combination of the immediate upstream and downstream cross-sections and the bridge geometry.

The HEC-RAS bridge modeling subroutine also requires the following information: the river, reach, and river station identifiers; a short description of the bridge; the bridge deck; bridge abutments (if they exist); bridge piers (if the bridge has piers); and specification of the bridge modeling approach. There are four methods available for computing losses through the bridge: Energy Equation (standard step method), Momentum Balance, Yarnell Equation and FHWA WSPRO method. The bridges at SR 92 and the Parkway were modeled using the Energy equation method as recommended by the HEC-RAS Hydraulic Reference Manual. The energy-based method treats a bridge in the same manner as a natural river cross-section, except the area of the bridge below the water surface is subtracted from the total area, and the wetted perimeter is increased where the water is in contact with the bridge structure. As described previously, the program formulates two cross-sections inside the bridge by combining the ground information of sections 2 and 3 with the bridge geometry. The railroad and CR 542 bridges were modeled using the Momentum balance method in accordance with the HEC-RAS Hydraulic Reference Manual. The momentum method is based on performing a momentum balance from previously described cross-section 2 to cross-section 3. The momentum balance is performed in three steps. The first step is to perform a momentum balance from cross-section 2 to a generated cross-section inside the bridge. The momentum balance method requires the use of roughness

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coefficients for the estimation of the friction force and a drag coefficient for the force of drag on piers. The drag coefficient value of 2.00 corresponding to a square-nose pier was used (Hydraulic Reference Manual, Table 5.3, p 5-13). The hydraulic computations used to compute the energy losses of the culverts located at Saddle Creek road and CR 540 are similar to the bridge hydraulic computations, except the Federal Highway Administration's (FHWA) standard equations for culvert hydraulics under inlet control are used to compute the losses through the structure. Because of the similarities between culverts and other types of bridges, the cross-section layout, the use of ineffective areas, the selection of contraction and expansion coefficients, and many other aspects of bridge analysis apply to culverts as well. Channel Roughness, Contraction and Expansion Coefficients In addition to structure loss coefficients, the HEC-RAS model utilizes a Manning's n value for channel friction loss, and contraction and expansion coefficients to evaluate transition losses. A Manning's n roughness coefficient was estimated from field survey for both the stream channel and floodplain for each reach of the model. Photographs taken during field survey activities also provided the basis for these assessments. The Manning’s n values used are 0.06 for the stream channel and 0.18 for the floodplain. Contraction and expansion coefficients are used to model energy losses where contraction and expansion of flow exists due to changes in channel cross-sections. Losses due to contraction and expansion of flow between cross-sections are determined during the standard step profile calculations. Manning's equation is used to calculate friction losses, and all other losses are described in terms of a coefficient times the absolute value of the change in velocity head between adjacent cross-sections. when the velocity head increases in the downstream direction, a contraction coefficient is used; and when the velocity head decreases, an expansion coefficient is used. In accordance with Table 5.2 of the HEC-RAS Hydraulic Reference Manual (reproduced as Table 9 below), values for those cross-sections other than the cross-sections just upstream or downstream of structures were set at .1 for contraction and .3 for expansion.

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Table 9. Sub-Critical Flow Contraction and Expansion Coefficients.

Contraction Expansion No transition loss computed 0.00 0.00 Gradual transitions 0.10 0.30 Typical bridge sections 0.30 0.50 Abrupt transitions 0.60 0.80

Source: HEC-RAS Hydraulic Reference Manual, p 5-8. Flow Data and Boundary Conditions HEC-RAS requires that at least one flow must be entered for every reach within the system. The flow values necessary to run the Saddle Creek hydraulic model were generated from the near-field surface water model. Peak flow values for existing conditions were used to compute surface water profiles for Saddle Creek. HES-RAS also requires that boundary conditions be set in accordance to the type of flow analysis being performed. A mixed flow regime was chosen as the flow calculation method for Saddle Creek. The mixed flow method requires that both upstream and downstream boundary conditions be specified. The boundary condition type used for the upstream boundary was “critical depth” and the downstream type was “known water surface.” The “known water surface” elevation used for both the 25 and 100 year model runs was the 100 year flood elevation for Lake Hancock. The elevation used was 102.1 feet and was taken from the Federal Emergency Management Agency’s 1982 Flood Insurance Study - Polk County, Unincorporated Areas (FEMA 1982). HYDRAULIC MODEL CALIBRATION Calibration of the HEC-RAS hydraulic (backwater) model for the Saddle Creek channel system requires a set of known historical elevations at locations within the watershed. Unfortunately, limited data were available for past events. The main mode of hydraulic model calibration is the adjustment of channel roughness coefficients (Manning's n). In the absence of sufficient calibration data, the roughness coefficients developed in the hydrologic model calibration model were input to the HEC-RAS hydraulic model as the best information available. The only source of stage/flow data that could be found within the study area were the stage recordings at the USGS’s Saddle Creek streamflow gage located at the SR 542 bridge (this gage was located approximately midway within the simulated channel system). The model was calibrated to daily average stage/flow values. The criteria for selecting which days to calibrate to is as follows:

(1) In order for the natural system to be compared to the steady state results of the simulation, the average daily flow of the day before and after the selected date should be similar to that of selected date.

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(2) The date selected should have a good match between the observed flows and the FHM simulated values. The simulated values were used for hydraulic calibration. The flows at each on the inflow points were not measured therefore simulated values were the best available data.

(3) A mix of high and low flows was required to calibrate and verify the model to

the extreme conditions.

When results of the HEC-RAS model simulation were compared to the stage/discharge of the USGS streamflow gage, there was good agreement. The hydraulic model was calibrated and verified, for this portion of the channel, on four different days. The results of the calibration are presented in Table 10.

Table 10. Calibration Results for the Hydraulic Model of Saddle Creek.

Date

FHM Average

Daily Flow at SR 542 Bridge

(cfs)

USGS Average

Daily Flow at SR 542 Bridge

(cfs)

HEC-RAS Stage Elevation

at SR 542 Bridge

(Ft. NGVD)

USGS Stage Elevation

at SR 542 Bridge

(Ft. NGVD) 9/25/98 371.23 373 105.91 106.03 4/7/98 111.46 114 103.91 104.25 2/24/98 318.58 327 105.60 105.82 12/14/96 16.28 16 102.53 101.90

HYDRAULIC MODEL RESULTS

The results of the 25- and 100-year flood study analysis of Saddle Creek are presented in the Appendix. The water surface profile is presented in Figure 127. It is noted that the water surface profile elevations generated by this study varies from flood profile presented in the Federal Emergency Management Agency’s 1982 Flood Insurance Study - Polk County, Unincorporated Areas (FEMA 1982). The most probable cause of this disparity is associated with the fact that the two studies used different peak inflow discharges. The water-surface elevations shown in the FEMA study were computed in a step-backward analysis using U.S. Geological Survey computer program E431. The peak inflow discharges used to run the E431 model were generated from a regional flood frequency analysis which was based on pre-1982 land use and hydrologic conditions. This study used peak inflow discharges generated by the near-field surface water model using current land use and hydrologic conditions.

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Figure 126. Simulated Water-Surface (WS) Elevations for Saddle Creek 25-Year

and 100-Year Simulations.

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CONCLUSIONS AND RECOMMENDATIONS Conclusions and recommendations are presented and organized according to the five primary objectives of the project: (1) construct an integrated surface water/groundwater of the upper Saddle Creek watershed; (2) evaluate historical trends in the hydrology of the Upper Saddle Creek watershed; (3) evaluate the potential for wetland restoration in the Saddle Creek and Tenoroc Fish Management Area using existing and alternative wetland systems; (4) demonstrate the utility of FHM for large-scale landform restoration; and (5) provide predictive capabilities of surface and groundwater flows to Saddle Creek and Lake Hancock. MODEL DEVELOPMENT AND CALIBRATION When this project was initiated, a conceptual model of the ground-water regime in a mined area was constructed. In this conceptualization, the surficial aquifer in a mined area was assumed to be highly heterogeneous as a result of mining activities. Initially, efforts were made to reconstruct the mining history of the area to aid in delineating areas of similar hydraulic characteristics. In addition to this conceptual-historical approach, a series of shallow, water-table monitor wells were installed within the Tenoroc site. Construction of these wells also provided valuable data on the surficial aquifer which aided model conceptualization.

During the period of observation, it was noted that water-table elevations and the elevations of the potentiometric surface of the Floridan Aquifer were highly correlated. This led to a conclusion that, at the scale of the near-field model representing the Tenoroc site, lateral flow in the surficial aquifer is not a major component of the ground-water system, but vertical flow between the surficial and Floridan Aquifers is a major component. The model calibration for the near-field model compares reasonably well to the observed data of the three-year period. The scale of the near-field domain allows predictions of the hydrologic system within the Saddle Creek watershed down to Lake Hancock. The scale of the model is probably inappropriate to represent the details required to design the structures for various reclamation alternatives but rather it gives an overall water budget analysis of the proposed alternatives. The water budget results from the alternative simulations also illustrates the impacts of the various scenarios on the hydrology of surrounding features and for the entire watershed. The alternative analyses of the Saddle Creek Watershed included in this report were performed as a first step to determine the relative impacts on the system. These simulations can be used as a first phase of alternative selection. Further work is necessary for the detailed design of the various alternatives. During calibration of the near-field groundwater model, a good match was achieved between observed and calculated water-table elevations. This was achieved

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without including unnecessary heterogeneity in the surficial aquifer, and with a relatively simple zonation of the leakance coefficient between the water-table and Floridan aquifers. This zonation of leakance was optimized using the statistical parameter estimation program PEST. The success of a relatively simple representation of the water-table aquifer system in the near-field model at reproducing the observed water-table elevations during a period when water-table elevations exhibited large fluctuations could be the result of several factors. First, the conceptualization that horizontal flow in the surficial aquifer is not a major component of the flow system may be considered valid. It is also possible, however, that the available field data do not provide enough density spatially to resolve small-scale, lateral-flow components in the water-table system. It is hydrologically plausible that the surficial aquifer system may provide significant long-term storage of water which is released to the surface-water system during dry periods. This interaction would probably be most effective over distances of a few hundred feet, at most, from surface-water bodies. A more detailed water-table elevation monitoring network would be required to determine if lateral ground-water flow (essentially bank storage) is a significant component of the total system. The current near-field model does not include, nor appears to require, such a small-scale conceptualization of the water-table system. The physical processes could be easily masked by “calibration” and parameterization of the surface water model and the groundwater model, whereby short period (days) groundwater fluxes would easily be represented by increased storage attenuation, coupled with erroneously high runoff rates from the surface water model. HISTORICAL TRENDS IN THE UPPER SADDLE CREEK WATERSHED

Historically, the Upper Saddle Creek watershed represented the lower extremity of the Green Swamp which forms the head waters of four major river systems in west central Florida: the Hillsborough, Alafia, Peace, and Withlacoochee Rivers. Analysis of undisturbed surficial soil in a review of the historical soil series information and boring trends around the site indicate moderately heavy hydric soils with significant clay fractions with characteristically low permeabilities. In addition, historically surficial and Floridian aquifer levels were at or above grade in the domain. A long-term decline in groundwater (potentiometric) levels has occurred associated with the increased utilization of this aquifer for industrial, agriculture, and domestic water supply, which has resulted in associated streamflow and baseflow reductions (Taylor 1997, Hammett 1990). The exact source of the groundwater declines cannot be attributed to just one use, because significant impacts of various types have occurred within the greater groundwater basin. There has been a threefold increase in potable water supply in the basin which extends to Tampa Bay community and the intense agricultural area to the southwest. Historically high groundwater utilization for industrial (mining) purposes has diminished while domestic and agricultural uses have increased. There has been an overall decline in the potentiometric heads. In addition, the roles of drainage alterations and increased

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imperviousness (associated with urbanization) within the rapidly changing basin land use is uncertain. Groundwater levels and associated streamflow discharges rebounded briefly to near historic levels during the uncharacteristically wet El Niño period of 1997-98. The significant drought following this period resulted in rapid declines in the water table and potentiometric heads which reversed this increasing flow trend. One objective of the wetland restoration in the Saddle Creek watershed would therefore provide for more sustained low flow discharges while reducing high flow periodicity from urbanization.

POTENTIAL FOR LARGE-SCALE WETLAND RESTORATION

Seven basic alternatives were investigated to evaluate the potential for hydro-period restoration of the Upper Saddle Creek watershed and to provide alternative water sources to Tenoroc Fish Management Area. The alternatives range from relatively minor flow system alterations to significant rerouting of the principal tributaries: the Eastern, Central, and Western ditches of the Upper Saddle Creek watershed. Predicted simulations were made for the various alternatives and results presented in terms of full hydro-period restoration, ability to impound and create additional wetland areas in Tenoroc Fish Management Area, and downstream hydro-period periodicity especially with regards to flooding. While a detailed flood plain model was created for the Upper Saddle Creek watershed to investigate flood plain issues associated with these alternatives, keeping with the scope of the project, this model was only set up and calibrated for background conditions and is awaiting use for predictive simulations as the alternative analyses are further defined. A major consideration associated with the alternatives of rerouting substantial flow tributaries in the Tenoroc area is the safety and security of aging structures controlling impoundments on the Fish Management Area. Most of the structures are in excess of 20 years of age and were mostly temporary structures designed to meet mining needs during active mining years and were never replaced. They are basically in poor condition and no additional stresses should be placed on the structures such as increasing the stage of water levels or routing additional storm flows. Any modification should be a concern as to stability from a safety consideration. While further analysis needs to be made, it appears the greatest potential for additional freshwater sources for wetland restoration efforts would be those sources originating from the Western Ditch tributary. Other wetland restoration alternatives should be considered and prioritized by the relative ability of the volume of water associated with the Western Ditch system.

APPLICATION OF THE FHM FOR LARGE-SCALE MINED LAND RECLAMATION

The FHM has been shown to be capable of being used on the complexity of the Upper Saddle Creek watershed with large-scale mine reclamation activity (some ongoing during the project), large-scale urbanization, and significant water diversions within the system. Many new features have been added to the FHM to allow for its implementation for regional watershed investigations. Most new features stem from the need to provide

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for much greater discretization and much longer and more heavily discretize meteorological time series, for example rainfall. It is concluded that the model has reasonable predicative capability for the hydrologic conditions of the basin within the bounds of similar rainfall records measured during the calibration field effort.

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REFERENCES Cathcart JB. 1964. Economic geology of the Lakeland Quadrangle, Florida. Washington: U.S. Government Printing Office. U.S. Geological Survey Bulletin 1162-G. Federal Emergency Management Agency (FEMA). 1982. Flood insurance study—Polk County, Florida, unincorporated areas. Washington (DC): Federal Emergency Management Agency. Geurink JS, Tara PD, Stewart MT, Ross MA. 1995a. A GIS-based multi-scale integrated model for comprehensive water management evaluation, Task Three report: multi-scale groundwater model development and simulation. CMHAS Water Resources report, SWFWMD.97.02. Tampa (FL): University of South Florida. Geurink JS, Baudean JA, Tara PD, Stewart MT, Ross MA. 1995b. A GIS-based multi-scale integrated model for comprehensive water management evaluation, Task Four report: surface water and FHM Integrated Model development and simulation. CMHAS Water Resources report, SWFWMD.97.01. Tampa (FL): University of South Florida. Geurink JS, Stewart MT, Ross MA. 1995c. A GIS-based multi-scale integrated model for comprehensive water management evaluation, Task One report: data collection and assessment. CMHAS Water Resources report, SWFWMD.95.01. Tampa (FL): University of South Florida. Geurink JS, Langevin C, Tara PD, Stewart MT, Ross MA. 1995d. A GIS-based multi-scale integrated model for comprehensive water management evaluation, Task Two report: groundwater model development and simulation. CMHAS Water Resources report, SWFWMD.95.02. Tampa (FL): University of South Florida. Hammett KM. 1990. Land use, water use, streamflow characteristics, and water-quality characteristics of the Charlotte Harbor inflow area, Florida. U.S. Geological Survey Water Supply Paper 90-2359. 64 p. Hydrologic Engineering Center, U.S. Army Corp of Engineers. 1998a. HEC-RAS River Analysis System - User’s manual. Version 2.2. Davis (CA): U.S. Army Corps of Engineers. Hydrologic Engineering Center, U.S. Army Corp of Engineers. 1998b. HEC-RAS River Analysis System - Hydraulic reference manual. Version 2.2. Davis (CA): U.S. Army Corps of Engineers. Madrid Engineering Group, Inc. 1988. Landfill site evaluation - geotechnical, environmental and ecological evaluation of two sites for potential development, Lakeland, Florida. Prepared for Case Engineering and the City of Lakeland Department of Electric and Water Utilities, Project Number 2589. Lakeland, Florida.

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McKay L, Hanson S, Horn R, Dulaney R, Cahoon A, Olsen M, Dewald T. 1994. The U.S. EPA Reach File Version 3.0 Alpha Release (RF3-Alpha) technical reference. Washington (DC): U.S. Environmental Protection Agency, Office of Wetlands, Oceans, and Watersheds. Perry RG. 1995. Regional assessment of land use nitrogen loading of unconfined aquifers [DPhil thesis]. Tampa: University of South Florida. 229 leaves. Powers MR. 1999. Reclaimed phosphate clay settling area investigation hydrologic model calibration and ultimate clay elevation prediction. Bartow (FL): Florida Institute of Phosphate Research. FIPR project nr 94-03-109S. Ross and others. 1992, 1993, 1994. FIPR Hydrologic Model: volumes 1 and 2, technical and users’ documentation. University of South Florida, Center for Modeling Hydrologic and Aquatic Systems and Florida Institute of Phosphate Research. Bartow (FL): Florida Institute of Phosphate Research. Ross MA, Tara PD, Geurink JS, Stewart MT. 1997. FIPR Hydrologic Model users’ manual and technical documentation. Tampa: University of South Florida. CMHAS Water Resources Report FIPR.97.03. Strahler AN. 1957. Quantitative analysis of watershed geomorphology. Transactions, American Geophysical Union 38:913-20. Taylor M. 1997. Investigation of stream/aquifer response in two Florida watersheds [MS thesis]. Tampa: University of South Florida. 77 leaves.

APPENDIX A

SURVEYED CROSS-SECTIONS

Figure A-1. Surveyed Cross Sections 30000, 29000, 800, 700.

A-1

Figure A-2. Surveyed Cross Sections 28000, 25000, 24000, 23000.

A-2

Figure A-3. Surveyed Cross Sections 22000, 21900, 21500, 21000.

A-3

Figure A-4. Surveyed Cross Sections 20900, 20700, 20600, 20400.

A-4

Figure A-5. Surveyed Cross Sections 20000, 17000, 16000, 15000.

A-5

A-6

Figure A-6. Surveyed Cross Section 14000.