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Lessons From Hurricane Ike

Lessons From Hurricane Ike

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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