Proposed Hazard Module Expert Panel Open Meeting Austin, Texas March 13, 2014

1. Proposed Hazard Module Expert Panel Open Meeting Austin, Texas March 13, 2014

2. Agenda • Introductions • Overview • Proposed Hazard Module • Wind • Wave and Surge Flooding • Timing and Delivery of Hazard Module • Future Work • Q&A

3. Introductions • Sam Amoroso, Ph.D. P.E., S.E. Forte & Tablada, Inc. • Bob Bailey, Ph.D., P.E. Exponent, Inc. • Bill Coulbourne, P.E. Coulbourne Consulting • Andrew Kennedy, Ph.D. University of Notre Dame • Doug Smith, Ph.D., P.E. Texas Tech University

4. Overview • 1st Open Meeting • Austin, August 22, 2013 • Develop Framework Plan • 2nd Open Meeting • Corpus Christi, December 10, 2013 • 3rd Open Meeting • Austin, March 13, 2014

5. 1st Open Meeting • Panel Member Backgrounds • The TWIA expert panel has been appointed under Insurance Code §2210.578 and 28 Texas Administrative Code §§5.4260-5.4268. The panel’s purpose is to develop ways of determining whether a loss to TWIA-insured property was caused by wind, waves, tidal surges, or rising waters not caused by waves or surges. • After the panel completes its work, the commissioner will consider the panel’s findings and publish guidelines that TWIA must use to settle claims.

6. 2nd Open Meeting • Present Preliminary Overall Methodology • Initial Focus: Residential Slab Only Claims

7. Preliminary Overall Methodology

8. Proposed Hazard Module • Wind • Dr. Doug Smith • Objectives • Methodologies • Model Classes and Investigations • Recommendations • Wave and Surge Flooding • Dr. Andrew Kennedy • Wave and Surge Definitions • Model Requirements • Technical Requirements • Coupled Wave and Surge Models • Wave and Surge Measurements

9. Wind

10. Objectives for Hazard Module Goals • Site Specific: • wind speed time history • wind direction time history • surge time history • wave time history • Minimum of error • Used to predict damage to individual structure as the storm passes

11. Hazard Timing 12 m/s 75 deg 2.2 ft 10 ft

12. Hazards Module Flow Chart Steps • Collect Hurricane Wind Field Data over Life of Storm. • Develop Global Hurricane Wind Field. • Use the hurricane wind field as input to surge model and wave model. • Obtain time correlated histories. • Refine the time histories. • Final time histories for vulnerability module.

13. Wind Hazard Component • Two purposes • Input for surge and wave module • Input for wind damage prediction module • Wind speed and direction at mean roof height (MRH) • Adjusted for upwind terrain MRH

14. Methodologies • Physical Measurements • Wind • Surge • Models • Wind field model • Surge model • Wave model • Combination of measurement and modeling

15. Physical Measurement

16. Model Classes • Parametric • Easy to use numerical model. • Requires minimal computational power. • Observational • Wind field constructed using objective analysis from surface wind speed measurements. • Requires minimal to moderate computational resources. • Dynamical Numerical Weather Prediction • Wind field constructed from sophisticated equations sets. • Requires significant computational resources.

17. Model Classes 1Hurricane Research Division Hurricane Wind 2Letchford Norville Schroeder Smith and Associates Wind Field Analysis 3Oceanweather, Inc Interactive Objective Analysis System 4Hurricane Weather Research and Forecasting 5Geophysical Fluid Dynamics Laboratory

18. Model Investigation • Models • Holland (symmetric) with translation • Modified Holland (asymmetric) with translation • H*WIND • LNSS WFA • Evaluation Criteria • Model output wind speed compared to surface observations • Desire minimum error • Hurricane Ike

20. Hurricane Ike at Landfall

21. Surface Observations for Error Investigation

22. TTU 110 Center of Storm

23. TTU 110 Time History Comparisons

24. TTU 102 NE Wind Max

25. Model Comparison

26. TTU 220 West of Track

27. Model Comparison

28. Bulk Errors

29. Errors at H*Wind Time Steps

30. Errors at All LNSS WFA Steps

31. Errors at time steps where both H*Wind and LNSS WFA exist

32. Summary

33. Recommendations • Use an observational wind field for the hurricane wind field model. • High spatial and temporal resolution • Produce wind speed and direction time histories with minimum of error • Increase the number of surface observations contributing to the observational wind field (e.g. using pre-positioned or mobile platforms) to improve accuracy. • Embed the observational wind field in a larger synoptic model for surge and wave modeling. • Use local observational wind field analysis to refine wind time histories if necessary.

34. Storm Surge Flooding

35. Wave and Surge Hazard • Texas has experienced numerous catastrophic wave and surge events during hurricanes. The two most notable are: • 1900 Great Galveston Hurricane • Hurricane Ike (2008) • Thousands of buildings were destroyed in each of these storms. • Particularly for post-storm slab cases, knowledge of wave and surge hazard levels (storm surge, waves heights) is needed to help separate wave/surge and wind damage.

36. Models and Measurements • Both direct measurements and models will be important in establishing wave heights and surge elevations. • For TWIA, both are most important in built up regions with insured properties. • Models and measurements will both be used to determine hazard levels (waves and surge) at properties. • Resulting hazard levels will aid in adjusting claims.

37. Wave and Surge Definitions • Separate inundation into waves and surge • Surge is the slow variation of average water levels over periods of 10 minutes or longer • Waves are the faster variation of water levels • Like waves at the beach • Typically 5-20s periods dominate in hurricanes • At a given location wave and surge properties will define the hazard. • When combined with the structural properties, these will allow damage estimates.

38. Model Requirements (Waves and Surge) • To be most useful to TWIA, models will need to have certain properties relating to accuracy and usability. • There may be more than one choice of model that meets requirements. • Models will need to be set up well before any storm so they may be run quickly after the storm. • Models should give predictions of waves and surge that are as accurate as possible for a hurricane impacting the Texas Coast. • The region most important for accuracy is on normally dry ground, at insured properties. • Models should be validated against historic storms.

39. Technical Requirements (Wave and Surge Models) • Models should not just include the Texas Coast, but will need to encompass the Gulf of Mexico. • Grid resolution needs to be as fine as possible in the vicinity of insured properties (20-80m). • Wave and surge models should be tightly coupled. • Models should be easily modified to account for post-storm changes/erosion to dunes and shoreline. • Model should have an accurate wind field model that is consistent with the wind hazard module. • Surge model should include tides.

40. Example Topographic Detail – Coarse Grid Source: Bailey, 2010, “Probable Maximum Surge and Seiche Flooding,” Presentation to the Nuclear Regulatory Commission.

41. Example Topographic Detail – Fine Grid Source: Bailey, 2010, “Probable Maximum Surge and Seiche Flooding, ” Presentation to the Nuclear Regulatory Commission.

42. Example of High Resolution Hurricane Ike Simulation using SWAN+ADCIRC • SWAN computes waves, ADCIRC computes surge. • May not be the only model choice that could give good results. • 18 million element simulation using hindcast winds (high accuracy reconstruction). • Resolution down to 20m in some complex areas. • Runs on parallel computer (like all high resolution simulations). • Tides included. • Comparisons against high water marks, NOAA gauges, rapidly installed gauges.

43. Grid Resolution on the North Gulf Coast Maximum Surge Levels Source: Hope et al. (2013). JGR-Oceans, 118, 4424-4460.

44. Model Comparison with Ike High Water Marks • Two shades of green indicate model predictions to within ±0.5m (1.6 feet) • Very good accuracy around Texas Coast Source: Hope et al. (2013). JGR-Oceans, 118, 4424-4460.

45. Model Comparison with Wave Height Measured SWAN STWAVE Scatter Index: 0.2603 (lower is better) • All data are offshore of land • Overland accuracy lower Source: Hope et al. (2013). JGR-Oceans, 118, 4424-4460.

46. Loss of Accuracy with Fewer Grid Points • 18 million vs 827,000 element simulations • R2 decreases from 0.823 to 0.758 (higher is better) • RMS error from 0.284m (0.9ft) to 0.356m (1.2ft) Medium Resolution • Two shades of green indicate model predictions to within ±0.5m (1.6 ft) High Resolution Source: Kerr et al. (2014a). JGR-Oceans, 118, 4633-4661.

47. Loss of Accuracy with Very Few Grid Points • 827,000 (ADCIRC) vs 185,000 element (SLOSH) • R2 decreases from 0.716 to 0.555 (higher is better) • RMS error from 0.486m (1.6ft) to 0.961m (3.2ft) Low Resolution • Different Models Used (ADCIRC vs SLOSH) Source: Kerr et al. (2014b). JGR-Oceans, 118, 5129-5172. Medium Resolution

48. Coupled Wave and Surge Models • Inclusion of wave radiation stresses into surge model is necessary to achieve maximum accuracy. • Gives Wave Setup in nearshore. • In high resolution model Ike simulation, R2 decreases from 0.832 to 0.785 if waves are not included. • RMS error increases from 0.284m (0.9ft) to 0.334m (1.1ft).

49. Wave and Surge Measurements • Direct measurements of waves and surge near insured properties will help to improve evaluations of hazard levels. • Continuously recording pressure measurements with high temporal resolution will provide the best combination of accuracy and cost efficiency. • Instruments will likely need to be rapidly installed pre-storm, based on the storm track. • High Water Marks can give good data post-storm. • It may prove best to couple with external partners to collect data.

50. Example USGS Measurements • Bolivar Peninsula, Direct Oceanfront. • Installed directly before storm. • Processed data provides evaluation of both surge elevation and wave height over time. Source: East et al. (2008). USGS Open-File Rep. USGS 2008-1365.