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

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

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

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

History of Coastal Floodplain Mapping to 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 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

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

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

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

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

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

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

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

Case Study: Plymouth Harbor ASFPM 2011 Ongoing study update for Plymouth Harbor Extratropical events dominate 1991 Halloween Nor’Easter Public relevance

Case Study: Plymouth Harbor ASFPM 2011

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

Case Study: Plymouth Harbor ASFPM 2011

Case Study: Plymouth Harbor ASFPM 2011

Case Study: Plymouth Harbor ASFPM 2011

Case Study: Plymouth Harbor ASFPM 2011

Case Study: Plymouth Harbor Location Wave Period [sec] ACESSTWAVE Plymouth Harbor Duxbury Harbor Exterior Coastline ASFPM 2011 Location Wave Height [m] ACESSTWAVE Plymouth Harbor Duxbury Harbor Exterior Coastline

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

Questions ASFPM 2011