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Lessons From Hurricane Ike

This chapter delves into storm surge prediction using advanced modeling techniques revealed after Hurricane Ike. It highlights the significance of storm surges in hurricane damage and the evolution from historical data methods to sophisticated computer-based models like ADCIRC and SLOSH. The text explores key factors influencing storm surge, including wind speed, atmospheric pressure, and bathymetry. A case study of the proposed Ike Dike illustrates the use of ADCIRC for evacuation planning and structural testing to mitigate surge impact. Insights into real-time forecasting and community safety measures are also presented.

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Lessons From Hurricane Ike

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  1. Lessons From Hurricane Ike Chapter 5: Predicting Storm Surge

  2. overview • Introduction • Storm Surge Modeling • ADCIRC • Case Study: The Ike Dike

  3. Introduction • Hurricanes inflict damage through wind, rainfall, tornadoes, and surge • Storm Surge - an offshore rise of water associated with a low pressure weather system, caused by • High winds • Low Pressure • Bathymetry (Underwater Topography)

  4. Introduction • Storm surges cause the most damage • Seawalls, levees, dikes, and bulkheads all protect against storm surge • Before modeling systems, storm surge prediction was based solely on historical data • Very inaccurate

  5. Storm surge Modeling • Predicting storm surge depends on a multitude of factors. • Wind speed • Wave-current interaction • Tides • Atmospheric pressure • Riverine flows • Rainfall • Topography • Bathymetry

  6. Storm Surge Modeling • Computer simulations are based on these factors • Allow modelers to forecast various storm surges • Use models to test structural and non-structural mitigations (Levees, wetlands, etc.) • Build and/or utilize the most impactful mitigation Houston flood simulation

  7. Storm Surge Modeling • Coastal communities have high risk for damaging surge • Storm surge modeling can forecast in real time • Helps decision makers identify and evacuate at risk populations well in advance

  8. Advanced circulation (Adcirc) • SLOSH - Sea, Land, and Overland Surges from Hurricanes model • Computer based modeling system • Developed in the 1960’s • Based on pressure, size, track, forward speed, and wind speed. • Allows forecasters to estimate potential surge with 20% accuracy

  9. Advanced circulation (Adcirc) • LIDAR – Light Detection and Ranging • Data collected by sensor that emits high frequency laser through the bottom of an aircraft • Sensor records time difference between emission and return of the laser signal to determine elevation • Data applied to storm surge model for more accurate predictions • SLOSH is still dependent on track of hurricane • If hurricane does not follow projected path, all predictions are useless

  10. Advanced circulation (Adcirc) • ADCIRC Model • originally developed to study effect of a catastrophic storm on southern Louisiana. • High-res model of Louisiana coast expanded after Katrina to Mississippi and Alabama, and now Texas • Constant current updates • Used by Army Core of Engineers, National Civil Engineering Laboratory, and many others • ASGS – ADCIRC Surge Guidance System • Predictive tool for storms • Used in conjunction with SLOSH

  11. Modeling with adcirc • Storm surge height is not directly related to windspeed • Surge can not be predicted from category of storm alone • Hurricane Camille (1969) • Category 5 • In 2005, residents who were safe from Camille did not evacuate for Katrina (category 3) • Katrina had a much more severe surge

  12. Modeling with Adcirc • Wind forcing • Causes water in front of the storm to pile up on its self • Atmospheric pressure • Surface water exposed to low pressure will rise • 0.39 inches rise in sea level per 1 millibar drop in pressure • Currents • Energy of a breaking wave exponentially related to current

  13. Modeling with adcirc • Rainfall • Increases riverine flow which increases water depth at outlets • Bathymetry • Shallower waters by the coast cause higher surge • LIDAR advanced modeling • Tidal dynamics • High or low tide • Wet or dry shoreline • Ike made landfall at high tide

  14. Case Study: The Ike dike • ADCIRC applications • Evacuation planning • Potential damage assesment • Proposed structural mitigation testing • The Ike Dike • Dike proposed to reduce storm surge post hurricane Ike • Used ADCIRC to develop and test

  15. Case Study: Ike Dike A B Path of hurricane Ike along with storm surge elevation D C

  16. Case Study: Ike Dike Landfall point scenarios for evaluation

  17. Case study: Ike Dike Ike path and “worst-case” Ike path

  18. Case Study: Ike Dike Original storm surge elevation Projected storm surge elevation

  19. Case Study: Ike dike Storm surge elevation without Ike Dike Storm surge elevation with Ike Dike

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