Potomac Waterfront Flood Mitigation Study - City of Alexandria

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F I N A L R E P O R T POTOMAC RIVER WATERFRONT FLOOD MITIGATION STUDY EVALUATION AND RECOMMENDATION OF MITIGATION MEASURES Prepared for The City of Alexandria, VA City Hall 301 King Street Alexandria, VA 22314 July 2010 URS Corporation 200 Orchard Ridge Drive, Suite 101 Gaithersburg, MD 20878 Project Number: 15298592
TABLE OF CONTENTS ACRONYMS AND ABBREVIATIONS............................................................................................................ VI EXECUTIVE SUMMARY ........................................................................................................................... ES-1 SECTION ONE: INTRODUCTION................................................................................................................ 1-1 1.1 Potomac River Flood Mitigation Study Overview..................................1-1 1.2 Background.............................................................................................1-1 1.3 Study Area..............................................................................................1-2 1.4 Report Organization................................................................................1-3 SECTION TWO: REFINEMENT OF MITIGATION MEASURES................................................................. 2-1 2.1 Summary of Initial Flooding Assessment ...............................................2-1 2.2 List of Comprehensive Flood Mitigation Measures ................................2-4 2.3 Refinement of Mitigation Options ..........................................................2-5 SECTION THREE: OVERVIEW OF FLOOD MITIGATION MEASURES ................................................... 3-1 3.1 Structural Mitigation Measures...............................................................3-1 3.1.1 Structural Flood Barriers.............................................................3-1 3.1.2 Acquire Properties ......................................................................3-2 3.1.3 Floodproofing .............................................................................3-3 3.1.4 Elevate Structures .......................................................................3-7 3.1.5 Increase Inlet and Road Elevations .............................................3-7 3.2 NonStructural Mitigations ......................................................................3-8 3.2.1 Improve Floodplain Zoning Ordinances......................................3-8 3.2.2 Elevate Internal Supplies and Goods.........................................3-12 3.2.3 Sandbagging and Other Temporary Measures...........................3-13 3.3 Other Measures.....................................................................................3-14 SECTION FOUR: TECHNICAL ANALYSES SUPPORT............................................................................. 4-1 4.1 Existing Data ..........................................................................................4-1 4.1.1 Building Elevation Data..............................................................4-1 4.1.2 Field Reconnaissance..................................................................4-3 4.2 Overview of Cultural Resources Context................................................4-3 4.2.1 Local Protection for Historic Properties......................................4-5 4.2.2 Federal Protection for Historic Properties...................................4-5 4.3 Overview of Natural Resources Context.................................................4-6 4.4 Repetitive Loss Properties ......................................................................4-7 4.5 Consideration of Sea Level Rise.............................................................4-8 SECTION FIVE: ECONOMIC VALUATION (BENEFIT-COST ANALYSIS) ............................................... 5-1 5.1 Defining the Scope of Analysis ..............................................................5-1 5.2 Calculation of Project Benefits ...............................................................5-2 5.3 Calculation of Project Costs....................................................................5-5 5.3.1 Acquisition..................................................................................5-5 5.3.2 Floodproofing .............................................................................5-5 5.3.3 Other Structural Mitigation Measures.........................................5-6 SECTION SIX: STRUCTURAL MITIGATION MEASURE CONCEPTS...................................................... 6-1 6.1 Floodwall................................................................................................6-1 6.1.1 Description of Alternative...........................................................6-1 28-JUL-10\\ i
Page 4 and 5: TABLE OF CONTENTS 6.1.2 Assumptions
Page 6 and 7: TABLE OF CONTENTS FIGURES Figure 1-
Page 8 and 9: ac acre A/E Architectural/Engineeri
Page 10 and 11: TES Transportation and Environmenta
Page 12 and 13: SECTION ONE: INTRODUCTION 1.1 POTOM
Page 14 and 15: Introduction Factory and Strand Str
Page 16 and 17: Refinement of Mitigation Measures S
Page 18 and 19: 8.8 ft Figure 2-2: Flood Levels Stu
Page 20 and 21: Refinement of Mitigation Measures T
Page 22 and 23: Refinement of Mitigation Measures s
Page 24 and 25: Overview of Flood Mitigation Measur
Page 26 and 27: 3.1.3 Floodproofing Overview of Flo
Page 28 and 29: FLOOD ELEVATION BASE FLOW Overview
Page 40 and 41: E LURAY AV E GLENDALE AV EARL ST N
Page 42 and 43: N ALFRED ST MUIRS CT S COLUMBUS ST
Page 44 and 45: Technical Analyses Support resource
Page 46 and 47: Table 4-1: Repetitive Loss Properti
Page 48 and 49: Technical Analyses Support climate
Page 50 and 51: 5.2 CALCULATION OF PROJECT BENEFITS
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Economic Valuation (Benefit-Cost An
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Economic Valuation (Benefit-Cost An
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6.1 FLOODWALL Structural Mitigation
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Structural Mitigation Measure Conce
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6.1.3 Potential Impacts Structural
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VDEQ Section 401 Certification VDE
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6.2.1 Description of Alternative St
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CLIENT PROJ RAMSAY AL SWIFTS AL S L
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6.2.4 Permitting/Approval Requireme
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6.2.5 BCA and Results Structural Mi
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6.3.2 Assumptions Structural Mitiga
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CLIENT PROJ REVISION NO SCALE WALES
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Site Plan Approval Structural Mitig
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North Union Structural Mitigation M
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CLIENT PROJ REVISION NO SCALE S ROY
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King Street Residential Structural
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Waterfront Commercial Structural Mi
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7.2 KING STREET Elevated Walkway Re
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Figure 7-2: Elevated Walkway at Wat
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Recommendations The elevated walkwa
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King/Strand Street Intersection Roa
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Figure 7-6: Floodwall behind Torped
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7.7 REPETITIVE LOSS PROPERTIES Reco
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Recommendations (USBC) and Internat
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SECTION EIGHT: REFERENCES Access Fl
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References Huber Technology, 2009.
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Appendix A Initial Ranking of Poten
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Appendix B Ordinance and Sandbag In
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Exhibit 1-2. Sample ordinance from
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5. The necessity to the facility of
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Appendix C Non-Prioritized Measures
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Figure 1: Duckbill Check Valve A ty
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Relocate external electrical boxes
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Last, Hurricane Preparedness inform
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Potomac River Waterfront Flood Miti
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Figure A1-12 Exhibit 2: Field Visit
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Exhibit 2: Field Visit Summary - Ju
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Fig A11-1 Exhibit 2: Field Visit Su
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Figure A18-1 Exhibit 2: Field Visi
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Figure 21-3 Exhibit 2: Field Visit
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Figure 2: Screen shot from NOAA Atl
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Potomac River Waterfront Flood Miti
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38 40 38 4 6 40 34 28 14 30 30 40 4
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46 44 38 44 42 40 42 44 44 36 22 36
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48 44 38 36 38 18 46 42 38 42 26 22
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CLIENT PROJ REVISION NO SCALE City
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Table 4: Detailed cost estimate for
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Exhibit 3: Various Elevated Walkway
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Exhibit 4-2: Elevated Walkway - Kin
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Appendix H Berm
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Roadway Drainage Additional Data Ta
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Appendix J Property Acquisition
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Appraisals Based on data from Appra
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Exhibit 2. Total Other Costs for Pr
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Table 4: North Union Acquisition Co
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Appendix K Floodproofing
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Exhibit 2. Window Replacement Costs
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Elevate or relocate the electric pa
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Overview Potential Federal Funding
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Table 1. HMA Funding Options by Pro
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Hazard Mitigation Assistance The De
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program comparisons (continued) ELI
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program information GovDelivery Not
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Potomac Waterfront Flood Mitigation Study - City of Alexandria

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