Withlacoochee River Watershed Initiative (H066) Model Scenario Report Prepared by September 20, 2015 Table of Contents Chapter Page EXECUTIVE SUMMARY 11 INTRODUCTION 13 AUTHORIZATION 13 ACKNOWLEDGEMENTS 13 BACKGROUND / PURPOSE 14 SCENARIO LOCATIONS 16 MODEL SIMULATIONS 18 SCENARIO 1: GREEN SWAMP RAILROAD BERMS 21 1.1. DESCRIPTION 21 1.2. MODEL SET-UP 23 1.3. RESULTS 25 1.4. CONCLUSION 29 SCENARIO 2: GREEN SWAMP RAILROAD BRIDGE PILINGS 30 2.1. DESCRIPTION 30 2.2. MODEL SET-UP 31 2.3. RESULTS 33 2.4. CONCLUSION 36 SCENARIO 3: GREEN SWAMP AND SR 471 37 3.1. DESCRIPTION 37 3.2. MODEL SET-UP 38 3.3. RESULTS 39 3.4. CONCLUSION 42 SCENARIO 4: HILLSBOROUGH RIVER OVERFLOW AT US 98 43 4.1. DESCRIPTION 43 4.2. MODEL SET-UP 44 4.3. RESULTS 46 4.4. CONCLUSION 47 Withlacoochee River Watershed Initiative (H066) Model Scenarios Report: September 2015 SCENARIO 5: BRIDGE CROSSINGS NEAR TRILBY AND LACOOCHEE 48 5.1. DESCRIPTION 48 5.2. MODEL SET-UP 50 5.3. RESULTS 51 5.4. CONCLUSION 53 SCENARIO 6: LAKE ORIOLE 54 6.1. DESCRIPTION 54 6.2. MODEL SET-UP 56 6.3. RESULTS 57 6.4. CONCLUSION 61 SCENARIO 7: WYSONG-COOGLER WATER CONSERVATION STRUCTURE 62 7.1. DESCRIPTION 62 7.2. MODEL SETUP 65 7.3. RESULTS 65 7.4. CONCLUSION 70 SCENARIO 8: FLOOD STORAGE 71 8.1. DESCRIPTION 71 8.2. MODEL SETUP 72 8.3. RESULTS 73 8.4. CONCLUSION 74 SCENARIO 9: WITHLACOOCHEE RIVER HIGH INITIAL WATER LEVEL COMPARISONS 75 9.1. DESCRIPTION 75 9.2. MODEL SETUP 76 9.3. RESULTS 79 9.4. CONCLUSION 83 SCENARIO 10: FLYING EAGLE BERM IN TSALA APOPKA 84 10.1. DESCRIPTION 84 10.2. MODEL SET-UP 86 10.3. RESULTS 87 10.4. CONCLUSION 92 Withlacoochee River Watershed Initiative (H066) Model Scenarios Report: September 2015 SCENARIO 11: TSALA APOPKA PRE-SETTLEMENT CONDITIONS 93 11.1. DESCRIPTION 93 11.2. MODEL SETUP 94 11.3. RESULTS 95 11.4. CONCLUSION 101 SCENARIO 12: TSALA APOPKA AND THE ORANGE STATE CANAL 102 12.1. DESCRIPTION 102 12.2. MODEL SET-UP 103 12.3. RESULTS 105 12.4. CONCLUSION 110 SCENARIO 13: TSALA APOPKA STRUCTURE SIZES 111 13.1. DESCRIPTION 111 13.2. MODEL SETUP 113 13.3. RESULTS 115 13.4. CONCLUSION 117 SCENARIO 14: TSALA APOPKA STRUCTURE OPERATIONS 119 14.1. DESCRIPTION 119 14.2. MODEL SETUP 121 14.3. RESULTS 121 14.4. CONCLUSION 123 SCENARIO 15: TSALA APOPKA OUTFLOWS AND ARROWHEAD ESTATES 124 15.1. DESCRIPTION 124 15.2. MODEL SETUP 126 15.3. RESULTS 126 15.4. CONCLUSION 129 SCENARIO 16: GREEN SWAMP ROCK FORMATIONS 131 16.1. DESCRIPTION 131 16.2. MODEL SET-UP 132 16.3. RESULTS 134 16.4. CONCLUSION 137 Withlacoochee River Watershed Initiative (H066) Model Scenarios Report: September 2015 SCENARIO 17: ROCKS NEAR JUMPER CREEK 138 17.1. DESCRIPTION 138 17.2. MODEL SET-UP 141 17.3. RESULTS AND ANALYSIS 142 17.4. CONCLUSION 143 SCENARIO 18 AND 19: MODIFICATIONS TO LAKE ROUSSEAU OUTFLOW TO THE LOWER WITHLACOOCHEE 144 18.1. DESCRIPTION 144 18.2. MODEL SETUPS 145 Scenario 18: Bypass Channel Expansion 146 Scenario 19: Barge Canal 147 18.3. RESULTS 149 18.4. CONCLUSIONS 150 REFERENCES 151 APPENDIX A: SCENARIO SUMMARIES 153 Tables Page Table 1 Storm Events Simulated Rainfall Amounts .............................................................................. 19 Table 8-1 Peak stage comparison at SR 200 and Arrowhead Estates ..................................................... 74 Table 9-1 Design Storm Rainfall Amounts ............................................................................................... 76 Table 9-2 High Initial Water Levels in Tsala Apopka................................................................................ 78 Table 13-1 Differences in Flows, Water Levels and Volumes with Structure Modifications .................. 116 Table 14-1 Summary of Changes to the Tsala Apopka Pools during the Mean Annual Storm Event ..... 122 Table 14-2 Summary of Changes to the Tsala Apopka Pools during the 10-Year Storm Event .............. 122 Table 15-1 Peak Stage Comparison: S-353 Scenario ............................................................................... 127 Table 16-1 Average Water Level Increase (inches) at Locations of Simulated Rocks ............................. 135 Table 18-1 Flow and Water Level Comparison at Bypass Spillway ......................................................... 149 Withlacoochee River Watershed Initiative (H066) Model Scenarios Report: September 2015 Figures Page Figure 1 Withlacoochee Watershed Boundary ..................................................................................... 15 Figure 2 Location of Withlacoochee River Model Scenarios ................................................................. 17 Figure 3 Low Initial Water Level ............................................................................................................ 18 Figure 4 High Initial Water Level ........................................................................................................... 19 Figure 1-1 Green Swamp Streams and Creeks ......................................................................................... 22 Figure 1-2 Historic Railroad Berms are used Today as Access for Land Management and Recreation ... 23 Figure 1-3 Historic Berms in the Green Swamp that were Removed for this Scenario ........................... 24 Figure 1-4 Existing Topography with Berms Present (left side) and Simulated Topography with Berms Removed (right side) ............................................................................................ 25 Figure 1-5 Peak Water Level Changes from Simulated Berm Removal .................................................... 26 Figure 1-6 Comparison of Flows for the Little Withlacoochee River at SR 471 for the 2004 Hurricanes 27 Figure 1-7 Comparison of Flows for the Withlacoochee River at SR 471 for the 2004 Hurricanes.......... 28 Figure 1-8 Comparison of Combined Flows for Devils Creek and Gator Hole Slough for the 2004 Hurricanes ............................................................................................................................... 28 Figure 1-9 Flow Volume Increases (acre-feet) with Historical Railroad Berms Removed ........................ 29 Figure 2-1 Remnant Bridge Pilings across the Withlacoochee River in the Green Swamp ...................... 30 Figure 2-2 Bridge Piling Log Jams along the Withlacoochee River in the Green Swamp ......................... 31 Figure 2-3 Profile and Cross Section of Log Jam ....................................................................................... 32 Figure 2-4 Comparison of Existing Flow Obstruction (left side) and Simulated Natural Condition (right side) ............................................................................................................................... 33 Figure 2-5 Log Jam Cross Section during High Water Event ..................................................................... 34 Figure 2-6 Comparison of Water Levels Upstream of Log Jam for the Mean Annual Storm ................... 35 Figure 2-7 Comparison of Water Levels Upstream of Log Jam for the 2004 Hurricanes ......................... 35 Figure 2-8 Comparison of Low Water (left side) and High Water (right side) at a Bridge Piling Log Jam in the Green Swamp near Dade City ......................................................................... 36 Figure 3-1 Locations of Major Stream and Culvert Crossings under SR 471 in the Green Swamp .......... 37 Figure 3-2 Looking Downstream at the SR 471 Bridge Crossing on the Withlacoochee River (2008) ..... 38 Figure 3-3 Digital Terrain with and without the Footprint of SR 471 at the Little Withlacoochee River . 39 Figure 3-4 Comparison of Flows on the Withlacoochee River at SR 471 for the 100-year Storm Event . 40 Withlacoochee River Watershed Initiative (H066) Model Scenarios Report: September 2015 Figure 3-5 Comparison of Flows for the Little Withlacoochee River at SR 471 ........................................ 41 Figure 3-6 Comparison of Combined Flows for Devils Creek and Gator Hole Slough .............................. 41 Figure 3-7 Percent Difference in Total Flow Volume for the 2004 Hurricanes ........................................ 42 Figure 4-1 Location of the Hillsborough River Overflow from the Green Swamp.................................... 43 Figure 4-2 Aerial View of the US 98 Bridge Crossing on the Hillsborough River ...................................... 44 Figure 4-3 Digital Terrain of the Hillsborough River at the US 98 Bridge ................................................. 45 Figure 4-4 Comparison of the Current US 98 Bridge Opening to the Natural Flow Path (black line) ...... 46 Figure 4-5 Peak Water Level Changes (inches) from the Simulated Removal of US 98 (2004 Hurricanes) .................................................................................................................... 47 Figure 5-1 Bridges crossing the Withlacoochee River near Trilby and Lacoochee ................................... 48 Figure 5-2 Bridge over the Withlacoochee River at SR 575 ...................................................................... 49 Figure 5-3 Bridge over the Withlacoochee River at US 301 ..................................................................... 49 Figure 5-4 Flooding in Trilby, FL from High Water on the Withlacoochee River in 1933 ......................... 50 Figure 5-5 Existing Terrain with Bridges and Roadway Berms near Trilby, FL .......................................... 51 Figure 5-6 Modified Terrain with Bridges and Roadway Berms Removed in the Model ......................... 51 Figure 5-7 Upstream Side of SR 575 during the