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Highways in the Coastal Environment: Assessing Extreme Events

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Highways in the Coastal Environment: Assessing Extreme Events Archival Superseded by HEC-25 3rd edition - January 2020 Publication No. FHWA-NHI-14-006 October 2014 U.S. Department of Hydraulic Engineering Circular No. 25 – Volume 2 Transportation Federal Highway Administration Archival Superseded by HEC-25 3rd edition - January 2020 Highways in the Coastal Environment: Assessing Extreme Events Archival Superseded by HEC-25 3rd edition - January 2020 TECHNICAL REPORT DOCUMENTATION PAGE Archival Superseded by HEC-25 3rd edition - January 2020 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Archival Superseded by HEC-25 3rd edition - January 2020 Table of Contents Table of Contents ........................................................................................................... i List of Figures ................................................................................................................ v List of Tables ................................................................................................................ vii Acknowledgements ........................................................................................................ ix Glossary ........................................................................................................................ xi List of Acronyms .......................................................................................................... xxi Chapter 1 – Introduction ................................................................................................ 1 1.1 Background ......................................................................................................... 1 1.2 Purpose ............................................................................................................... 1 1.3 Target Audience .................................................................................................. 3 1.4 Organization ........................................................................................................ 3 1.5 Units of this Document ........................................................................................ 4 1.6 Related Guidance................................................................................................ 4 Chapter 2 – Relevant Coastal Processes and Climate Change Impacts ........................ 7 2.1 Description of Relevant Coastal Processes ......................................................... 7 2.2 Damaging Processes of ExtremeArchival Coastal E vents ............................................... 7 2.2.1 Gulf of Mexico and South Atlantic Coast ..................................................... 8 2.2.2 Mid-Atlantic and New England Coast .......................................................... 9 2.2.3 Great Lakes Coast .................................................................................... 10 2.2.4 Pacific Coast ............................................................................................. 13 2.3 Climate Change Impacts on Damaging Coastal Processes ............................... 15 2.3.1 Sea Levels ................................................................................................ 15 2.3.1.1 Sea LevelSuperseded Rise Data .............................................................................. by HEC-25 16 2.3.1.2 Projections for Sea Level Rise ............................................................... 19 2.3.1.3 Example Calculation3rd edition of Projected -Future January Sea Level .............................. 2020 23 2.3.2 Lake Levels ............................................................................................... 25 2.3.3 Storm Surge .............................................................................................. 26 2.3.4 Waves ....................................................................................................... 27 2.3.5 Other Coastal Processes ........................................................................... 28 2.4 Numerical Models of Critical Coastal Processes ................................................. 29 2.4.1 Storm Surge Models ..................................................................................... 30 i 2.4.2 Wave Models................................................................................................ 32 2.4.3 Coastal Morphology Models ......................................................................... 32 2.4.4 Model Validation ........................................................................................... 33 Chapter 3 – Risk, Vulnerability and Adaptation ............................................................ 35 3.1 Engineering Risk at the Coast ........................................................................... 35 3.1.1 Return Period and Probability of Occurrence ................................................ 35 3.1.2 Coastal Storm Flood Frequencies ................................................................ 38 3.1.2.1 Atlantic and Gulf Coastal Surge Frequencies ........................................ 38 3.1.2.2 Pacific and Great Lakes Coastal Surge Frequencies ............................. 39 3.1.3 Available Estimates of Storm Surge – SSIMs and FIRMs ............................. 39 3.1.4 Other Approaches to Coastal Risk ................................................................ 40 3.2 Coastal Vulnerability Assessments .................................................................... 41 3.2.1 Vulnerability Assessments for Coastal Highways ......................................... 41 3.2.2 Vulnerability Assessment Framework ........................................................... 42 3.3 Climate Change and Extreme Events: Damage Mechanisms ............................ 44 3.3.1 Roadway Damage by Wave Attack .............................................................. 44 3.3.2 Roadway and Railway Damage by Coastal “Weir-Flow” ............................... 45 3.3.3 Roadway Damage by Bluff Erosion and Shoreline Recession ...................... 47 3.3.4 Bridge Deck Damage byArchival Waves on Surge .................................................... 47 3.3.5 Structure Damage by Wave Runup .............................................................. 49 3.3.6 Tunnel and Road Damage by Overtopping ................................................... 50 3.3.7 Damage by Tsunamis ................................................................................... 50 3.4 Adaptation Strategies for Coastal Highway Infrastructure .................................. 50 3.4.1 Manage and Maintain ................................................................................... 51 3.4.2 Increase RedundancySuperseded ................................................................................... by HEC-25 51 3.4.3 Protect .......................................................................................................... 51 3.4.4 Accommodate3rd .............................................................................................. edition - January 2020 53 3.4.5 Relocate ....................................................................................................... 53 Chapter 4 – Analysis Methods for Assessing Extreme Events and Climate Change .... 57 4.1 General Framework ........................................................................................... 57 4.1.1 Level of Effort 1: Use of Existing Data and Resources.................................. 57 4.1.2 Level of Effort 2: Modeling of Storm Surge and Waves................................. 58 4.1.3 Level of Effort 3: Modeling in a Probabilistic Risk Framework ....................... 59 ii 4.2 Gulf of Mexico and South Atlantic Coast ........................................................... 59 4.2.1 Level of Effort 1: Gulf of Mexico and South Atlantic Coast ......................... 60 4.2.1.1 Relative Sea Level Rise Data ................................................................ 61 4.2.1.2 Increased Flood Levels: Nonlinear SLR-Surge Relationship .................. 62 4.2.1.3 Coastal Land Elevation Data ................................................................. 62 4.2.1.4 Wave Characteristics ............................................................................. 62 4.2.1.5 Storm Surge Flow Velocity Estimates .................................................... 63 4.2.1.6 Other Considerations in Level 1 Studies ................................................ 63 4.2.2 Level of Effort 2: Gulf of Mexico and South Atlantic Coast ......................... 64 4.2.2.1 Storm Selection and Characterization.................................................... 64 4.2.2.2 Climate Change Scenarios .................................................................... 65 4.2.2.3 Surge and Wave Models ....................................................................... 66 4.2.2.4 Mapping of Results ................................................................................ 66 4.2.3 Level of Effort 3: Gulf of Mexico and South Atlantic Coast ......................... 67 4.3 Mid-Atlantic and New England Coast ................................................................ 69 4.3.1 Level of Effort 1: Mid-Atlantic and New England Coast .............................. 69 4.3.2 Level of Effort 2: Mid-Atlantic and New England Coast .............................. 70 4.3.3 Level of Effort 3: Mid-Atlantic and New England Coast .............................. 72 4.4 Great Lakes Coast ...........................................................................................
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