Potomac Waterfront Flood Mitigation Study - City of Alexandria

More documents

Recommendations

Info

Overview of Flood Mitigation Measures Add backflow preventers in homes to prevent stormwater and sewer backups. Isolate gas and electrical service lines. Relocate external electrical boxes. Improve the City’s emergency response. Inform businesses and residents about NFIP contents coverage. Improve/enhance existing business identification system. Provide updated information to residents. Provide education to area media outlets. 28-JUL-10\\ 3-15
4.1 EXISTING DATA SECTION FOUR: TECHNICAL ANALYSES SUPPORT Technical Analyses Support Key information used in the evaluation potential of flood mitigation measures included technical reference information listed in Section 8, References, and the City’s extensive GIS. The City maintains a robust GIS that includes topographic data, natural features, planimetrics, utilities, and other pertinent mapping data. The datum for the GIS is the North American Vertical Datum of 1988 (NAVD88). The City’s GIS data were used for all mapping products created for this study. The 100-year regulatory floodplain boundary from the City’s FIRM is also provided in the City’s GIS. The regulatory FIRM boundaries are the actual boundaries as shown on the FIRM, without regard to recent topographic data. Therefore, the regulatory floodplain does not necessarily match the topographic data. A plot of the 100-year floodplain elevation on the City’s GIS is a more accurate representation of the flood risk. The vertical datum of the FIRM is National Geodetic Vertical Datum of 1929 (NGVD29). The conversion to the NAVD88 datum for the Alexandria area is -0.8 feet. Thus, the FEMA 100-year flood elevation of 11.0 feet NGVD29 is 10.2 feet NAVD88. Figure 4-1 shows the calculated flood zone compared to FEMA’s regulatory floodplain boundary. The City and FEMA are in the process of updating the FIRM to reflect upto-date topographic data, and these maps were issued in a preliminary state on September 16, 2009. 4.1.1 Building Elevation Data Knowledge of the building elevation data is a key to determining the flood risk to properties. As described in the Initial Flood Assessment report, building elevation data used in this study was provided by the City from their GIS records. The City’s data showed over 300 buildings in the project areas that would be inundated by extreme flood. To supplement available FFE data, field survey for 35 residential and commercial structures was conducted. Careful consideration was taken in determining the structures for which additional survey would be most useful. Since the Waterfront Commercial focus area is the most floodprone location in the project area, first-floor elevations were obtained for all structures in the area where data were not already available. Outside of the Waterfront Commercial focus area, most of the buildings without known FFEs are residential row houses. Survey was conducted for these buildings with the assumption that if the FFEs were known for one or two houses in a row, the others could be reasonably estimated. In addition, a few of the available FFEs appeared to be inconsistent with field reconnaissance information, so some of those structures were selected to be surveyed to verify the accuracy of the data. Elevations were based on NAVD88 and horizontal position was specified in the Virginia Coordinate System of 1983 (VCS83). Control was set using a National Geodetic Survey (NGS) control monument, Global Positioning System (GPS) 52 (PID HV9658), in Founders Park across the street from 101 Queen Street. 28-JUL-10\\ 4-1
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 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
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
Page 62 and 63: 6.1.3 Potential Impacts Structural
Page 64 and 65: VDEQ Section 401 Certification VDE
Page 66 and 67: 6.2.1 Description of Alternative St
Page 68 and 69: CLIENT PROJ RAMSAY AL SWIFTS AL S L
Page 72 and 73: 6.2.4 Permitting/Approval Requireme
Page 74 and 75: 6.2.5 BCA and Results Structural Mi
Page 78 and 79: 6.3.2 Assumptions Structural Mitiga
Page 82 and 83: CLIENT PROJ REVISION NO SCALE WALES
Page 86 and 87: Site Plan Approval Structural Mitig
Page 88 and 89:
North Union Structural Mitigation M
Page 90 and 91:
Structural Mitigation Measure Conce
Page 92 and 93:
CLIENT PROJ REVISION NO SCALE S ROY
Page 94 and 95:
King Street Residential Structural
Page 96 and 97:
Waterfront Commercial Structural Mi
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
7.2 KING STREET Elevated Walkway Re
Page 104 and 105:
Figure 7-2: Elevated Walkway at Wat
Page 106 and 107:
Recommendations The elevated walkwa
Page 108 and 109:
King/Strand Street Intersection Roa
Page 110 and 111:
Figure 7-6: Floodwall behind Torped
Page 112 and 113:
7.7 REPETITIVE LOSS PROPERTIES Reco
Page 114 and 115:
Recommendations (USBC) and Internat
Page 116 and 117:
SECTION EIGHT: REFERENCES Access Fl
Page 118 and 119:
References Huber Technology, 2009.
Page 120 and 121:
Appendix A Initial Ranking of Poten
Page 122 and 123:
Appendix B Ordinance and Sandbag In
Page 124 and 125:
Exhibit 1-2. Sample ordinance from
Page 126 and 127:
5. The necessity to the facility of
Page 128 and 129:
Appendix C Non-Prioritized Measures
Page 130 and 131:
Figure 1: Duckbill Check Valve A ty
Page 132 and 133:
Relocate external electrical boxes
Page 134 and 135:
Last, Hurricane Preparedness inform
Page 136 and 137:
Potomac River Waterfront Flood Miti
Page 138 and 139:
Figure A1-12 Exhibit 2: Field Visit
Page 140 and 141:
Exhibit 2: Field Visit Summary - Ju
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Fig A11-1 Exhibit 2: Field Visit Su
Page 150 and 151:
Page 152 and 153:
Figure A18-1 Exhibit 2: Field Visi
Page 154 and 155:
Figure 21-3 Exhibit 2: Field Visit
Page 156 and 157:
Figure 2: Screen shot from NOAA Atl
Page 158 and 159:
Potomac River Waterfront Flood Miti
Page 160 and 161:
38 40 38 4 6 40 34 28 14 30 30 40 4
Page 162 and 163:
46 44 38 44 42 40 42 44 44 36 22 36
Page 164 and 165:
48 44 38 36 38 18 46 42 38 42 26 22
Page 166 and 167:
CLIENT PROJ REVISION NO SCALE City
Page 168:
Table 4: Detailed cost estimate for
Page 174 and 175:
Exhibit 3: Various Elevated Walkway
Page 176 and 177:
Page 178 and 179:
Exhibit 4-2: Elevated Walkway - Kin
Page 180 and 181:
Appendix H Berm
Page 182 and 183:
Page 184 and 185:
Roadway Drainage Additional Data Ta
Page 186 and 187:
Appendix J Property Acquisition
Page 188 and 189:
Appraisals Based on data from Appra
Page 190 and 191:
Exhibit 2. Total Other Costs for Pr
Page 192 and 193:
Table 4: North Union Acquisition Co
Page 194 and 195:
Appendix K Floodproofing
Page 196 and 197:
Exhibit 2. Window Replacement Costs
Page 198 and 199:
Elevate or relocate the electric pa
Page 200 and 201:
Overview Potential Federal Funding
Page 202 and 203:
Table 1. HMA Funding Options by Pro
Page 204 and 205:
Hazard Mitigation Assistance The De
Page 206 and 207:
program comparisons (continued) ELI
Page 208:
program information GovDelivery Not
show all

Potomac Waterfront Flood Mitigation Study - City of Alexandria

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?