Potomac Waterfront Flood Mitigation Study - City of Alexandria

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TES Transportation and Environmental Services Acronyms and Abbreviations TPS Total Station (Leica high performance total station series instrument) USACE United States Army Corps of Engineers USBC Uniform Statewide Building Code USGS U.S. Geological Survey VA Virginia VCS83 Virginia Coordinate System of 1983 VDEQ Virginia Department of Environmental Quality VDHR Virginia Department of Historic Resources VDHR DSS Virginia Department of Historic Resources Data Sharing System VMRC Virginia Marine Resources Commission VSMP Virginia Stormwater Management Program 28-JUL-10\\ viii
Executive Summary The City of Alexandria frequently experiences flooding from the Potomac River. The flooding affects residences, businesses, and infrastructure along the City’s waterfront. In 2006 the City commissioned the Potomac River Waterfront Flood Mitigation Study to identify and assess flooding problems and recommend solutions to reduce flood damages. In October 2007 an Initial Flooding Assessment Report was completed that identified specific flooding problems and their causes, and identified and categorized potential flood mitigation solutions. This report evaluates and recommends the most effective solutions. Twenty-seven mitigation measures were identified and discussed in a series of meetings with the City and the public. The following mitigation measures were selected for detailed evaluation. Structural measures: provide dry floodproofing; acquire properties; elevate structures; construct engineered structural barriers (i.e., waterfront floodwall and Jones Point Berm) construct an elevated walkway that would also be a floodwall structure; and increase the inlet and road elevation in the vicinity of the Lower King Street area. Nonstructural measures: relocate internal supplies, products/goods above the flooding depth; improve the City’s floodplain and zoning ordinances; and improve the sandbag programs or provide other temporary flood deterrents Rather than a single flood mitigation solution, a series of measures is recommended to provide protection against flood events on the Potomac River. Three structural measures are recommended: the elevated walkway, floodproofing, and the inlet and roadway improvements. The elevated walkway would provide flood protection for up to and including the 10-year flood event. It is a cost effective way to minimize the smaller flood events that frequently damage properties adjacent to the river. The low profile also minimizes the impact on the scenic views from the waterfront area. Dry floodproofing consists of a variety of methods to protect structures from flood waters during small storm events. These methods generally consist of removable barriers that could be installed in front of doors and windows to prevent flood waters from inundating the first floors of structures. King Street intersections with Strand Street and North Union Street are low points that frequently require road closures due to flooding. Raising the roadway profiles near these intersections will allow stormdrain catch basins and manholes to be elevated and reduce the frequency of road closures. These structural measures require significant capital expense and cooperation from private property owners. In addition, these projects call for significant effort to comply with applicable regulations. To further safeguard all properties, numerous nonstructural recommendations are made, which include improvement of the City’s floodplain ordinances and the existing sandbag program. Proceeding with implementation of the recommended flood mitigation measures is essential to reduce the frequent and extensive flood damage in the City. 28-JUL-10\\ ES-1
Page 2 and 3: F I N A L R E P O R T POTOMAC RIVER
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 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
Page 52 and 53: Economic Valuation (Benefit-Cost An
Page 54 and 55: Economic Valuation (Benefit-Cost An
Page 56 and 57: 6.1 FLOODWALL Structural Mitigation
Page 58 and 59: Structural Mitigation Measure Conce
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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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