Phase A - Alternatives Analysis Report - Urban Drainage and Flood ...

PHASE A – ALTERNATIVES ANALYSIS REPORTMajor Drainageway Planning Update for Hidden Lake-Bates LakeEXECUTIVE SUMMARY ........................................................................................................................................................ES-11 INTRODUCTION................................................................................................................................................................1-11.1 Authorization .................................................................................................................................1-11.2 Purpose and Scope .........................................................................................................................1-11.3 Summary of Data Obtained ...........................................................................................................1-11.4 Mapping Sources ...........................................................................................................................1-11.5 Data Collection ..............................................................................................................................1-12 STUDY AREA DESCRIPTION .........................................................................................................................................2-12.1 Project Area ...................................................................................................................................2-12.2 Land Use & Percent Impervious....................................................................................................2-12.3 Soils Information ...........................................................................................................................2-12.4 Reach Description..........................................................................................................................2-12.5 Flood History .................................................................................................................................2-22.6 Wetland and Riparian Zones..........................................................................................................2-23 HYDROLOGIC ANALYSIS ..............................................................................................................................................3-13.1 Overview........................................................................................................................................3-13.2 Design Rainfall ..............................................................................................................................3-13.3 Subwatershed Characteristics ........................................................................................................3-13.4 Hydrograph Routing ......................................................................................................................3-13.5 Previous Studies.............................................................................................................................3-23.6 Results of Analysis ........................................................................................................................3-24 HYDRAULIC ANALYSIS..................................................................................................................................................4-14.1 General...........................................................................................................................................4-14.2 Hydraulic Evaluation of Existing Facilities................................................................................... 4-14.3 Split Flow Areas ............................................................................................................................4-14.4 Flooded Areas ................................................................................................................................4-15 ALTERNATIVE DEVELOPMENTS ................................................................................................................................5-15.1 Alternative Development Process..................................................................................................5-15.2 Alternative Categories ...................................................................................................................5-15.3 Design Criteria...............................................................................................................................5-25.4 Hydraulic Evaluation .....................................................................................................................5-25.5 Alternative Plans............................................................................................................................5-25.5.1 Reach H-1 ..............................................................................................................................5-45.5.2 Reach H-2 ..............................................................................................................................5-65.5.3 Reach H-3 ..............................................................................................................................5-85.5.4 Reach H-4 ............................................................................................................................5-105.5.5 Reach B-1.............................................................................................................................5-125.5.6 Reach B-2.............................................................................................................................5-146 ALTERNATIVE EVALUATION ......................................................................................................................................6-16.1 Evaluation Process.........................................................................................................................6-1i6.2 Combination of Alternatives.......................................................................................................... 6-16.2.1 Reach H-1 ..................................................................................................................................... 6-16.2.2 Reach B-1...................................................................................................................................... 6-16.3 Flood Damage Evaluation.............................................................................................................. 6-26.4 Benefit-Cost Analysis .................................................................................................................... 6-26.5 Alternative Selection...................................................................................................................... 6-56.5.1 Reach H-1 ..................................................................................................................................... 6-56.5.1 Reach H-2 ..................................................................................................................................... 6-56.5.1 Reach H-3 ..................................................................................................................................... 6-56.5.1 Reach H-4 ..................................................................................................................................... 6-56.5.1 Reach B-1...................................................................................................................................... 6-56.5.1 Reach B-2...................................................................................................................................... 6-57 RECOMMENDED PLAN .................................................................................................................................................. 7-17.1 Plan Description............................................................................................................................. 7-17.2 Operations and Maintenance.......................................................................................................... 7-17.3 Recommended Plan Costs.............................................................................................................. 7-18 REFERENCES .................................................................................................................................................................... 8-1LIST OF TABLESTable ES-1 Comparison of Peak Flows Between ModelsTable ES-2 Summary of Costs for Recommended PlanTable ES-3 Project Participants and StakeholdersTable 2-1 Future Land UseTable 3-1 Rainfall DepthTable 3-2 Comparison of Peak FlowsTable 5-1 Alternative Unit Cost InformationTable 5-2 Reach H-1 Alternative Cost EstimatesTable 5-3 Reach H-2 Alternative Cost EstimatesTable 5-4 Reach H-3 Alternative Cost EstimatesTable 5-5 Reach H-4 Alternative Cost EstimatesTable 5-6 Reach B-1 Alternative Cost EstimatesTable 5-7 Reach B-2 Alternative Cost EstimatesTable 6-1 Reach H-1 Combination of Alternatives Cost EstimatesTable 6-2 Reach B-1 Combination of Alternatives Cost EstimatesTable 6-3 Building Damage PercentTable 6-4 Alternative Plans Costs and Benefit RatiosTable 7-1 Recommended Plan Cost Estimate and Benefit RatiosLIST OF FIGURESFigure 1 Study Area MapFigure 2-1 Future Land Use MapFigure 2-2 Future Percent Impervious MapFigure 2-3 Soils MapFigure 2-4 Reach Location MapFigure 2-5 100-Year FEMA Floodplains MapFigure 3-1 Sub-Basin Routing MapFigure 3-2 EPA SWMM Routing SchematicFigure 3-3 Hidden Lake Peak Discharge Profile