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Comparison of Wave Climate Analysis Techniques in Sheltered Waters May 19, 2011 Tim Hillier, P.E., CFM Associate Lauren Klonsky Water Resources Engineer

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Coastal Models: A Value Added Proposition Objective: Engender an open discussion regarding the perceived and technical significance of hydrodynamic models for coastal flood hazard studies. What is the relative precision as compared to analytic methods? What is the level of precision required for flood insurance studies? Where is the tipping point? ASFPM 2011

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Coastal Models: A Value Added Proposition What this presentation does NOT do: Validate or negate specific models Recommend a singular study approach for FEMA studies Propose that hydrodynamic models are not necessary ASFPM 2011

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Purpose of Coastal Flood Hazard Studies Deliver quality data that increases public awareness and leads to action that reduces risk to life and property ASFPM 2011

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History of Coastal Floodplain Mapping 1968 1973 1977 1979 1981 1986 to 1988 1988 1989 1995 2002 2005 2007 NFIP Authorized H b = 3' NAS Develops Wave Analysis Methodology FEMA Adopts NAS Methodology Runup Methodology Accepted Wetland Vegetation Muddy Bottom Erosion Analysis (540SF) PFD CERC TR 89-15 G&S for Wave Elevation and V Zone Mapping Appendix D Proc. Memo No. 37 Atlantic Ocean and Gulf of Mexico Guidelines Update (Final Draft) ASFPM 2011

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History: Coastal Modeling Development Lewis Fry Richardson (1920s) 6 hour forecasts for two points; 6 weeks LOE Computer Simulations (1950s) Rossby (1954) Joint Weather Prediction Unit (1955) Norman Phillips (1956) First successful climate model NOAA Geophysical Fluid Dynamics Laboratory (late 1960s) Development of Regional Models (1970s/1980s) Effects of soil/vegetation Advanced Circulation Model (1990s) Luettich and Westerink ASFPM 2011

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History: Coincidence of FIS and Models Synthetic Northeaster Model (1978) Simple Model Development (Mid-1980s) WHAFIS RUNUP 1-D Routing Routines (DYNLET) FEMA Surge (1988) Advent of Two-Dimensional Models (1990s) Water Surface Wave Climate Sampling Techniques (late 1990s to Present) EST JPM and JPM-OS ASFPM 2011

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Benefits of Hydrodynamic Models: Technical Provides a numerical description of a system by which the investigator can observe the impacts of variable inputs on the system Ability to characterize multiple events based on limited localized input Hindcasting Increase resolution of study domain ASFPM 2011

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Benefits of Hydrodynamic Models: Perceived Second approach for a typical appeal is to question the technical validity of the study techniques Getting into the weeds Literally Were the state-of-art techniques used? Application of hydrodynamic models and associated modeling routines is indicative of a fully detailed study ASFPM 2011

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Limitations of Hydrodynamic Models Cost Calibration with limited measured data Engineering decisions and Assumptions ASFPM 2011 Relationship of Accuracy to Cost Tipping Point

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Limitations of Hydrodynamic Models Model data is used as input to 1-D models WHAFIS Wave runup routines Coastal BFEs are mapped to the whole foot Mapping Decisions Primary Frontal Dune Erosion approaches Topography ASFPM 2011

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Guidance for Sheltered Waters Guidance for Coastal Flood Hazard Analyses and Mapping in Sheltered Waters (February 2008) Addresses two study categories: New studies Existing studies under which sheltered water bodies require additional assessment Transformation vs. Generation Water Level Wave Conditions and Wave Setup Erosion and Coastal Structures Overland Wave Propagation and Wave Runup ASFPM 2011

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Case Study: Plymouth Harbor ASFPM 2011 Ongoing study update for Plymouth Harbor Extratropical events dominate 1991 Halloween NorEaster Public relevance

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Case Study: Plymouth Harbor ASFPM 2011

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Case Study: Plymouth Harbor Study Approaches: Comparison of wave climate analyses Offshore Inshore Numerical and Analytical Techniques Steady State Wave Model (STWave) Automated Coastal Engineering Software ASFPM 2011

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Case Study: Plymouth Harbor ASFPM 2011

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Case Study: Plymouth Harbor ASFPM 2011

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Case Study: Plymouth Harbor ASFPM 2011

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Case Study: Plymouth Harbor ASFPM 2011

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Case Study: Plymouth Harbor Location Wave Period [sec] ACESSTWAVE Plymouth Harbor0.33.0 Duxbury Harbor2.03.0 Exterior Coastline6.010.0 ASFPM 2011 Location Wave Height [m] ACESSTWAVE Plymouth Harbor0.010.16 Duxbury Harbor0.270.17 Exterior Coastline2.653.71

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Conclusions Decision to model has several considerations Physical Characteristics Budget Perception Degradation of model precision in translation to maps Calibration with measured nearshore data ASFPM 2011

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Questions ASFPM 2011