Lessons From Hurricane Ike
Chapter 5: Predicting Storm SurgeLessons From Hurricane Ike
overviewIntroduction
Storm Surge Modeling
ADCIRC
Case Study: The Ike Dike
IntroductionHurricanes inflict damage through wind, rainfall, tornadoes, and surge
Storm Surge - an offshore rise of water associated with a low pressure weather system, caused byHigh windsLow PressureBathymetry (Underwater Topography)
IntroductionStorm 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
Storm surge ModelingPredicting storm surge depends on a multitude of factors.
Wind speed
Wave-current interaction
Tides
Atmospheric pressureRiverine flows
Rainfall
Topography
Bathymetry
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 simulationStorm Surge ModelingCoastal 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
Advanced circulation (Adcirc)SLOSH - Sea, Land, and Overland Surges from Hurricanes model
Computer based modeling system
Developed in the 1960s
Based on pressure, size, track, forward speed, and wind speed.
Allows forecasters to estimate potential surge with 20% accuracy
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
Advanced circulation (Adcirc)ADCIRC Modeloriginally 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 TexasConstant current updatesUsed by Army Core of Engineers, National Civil Engineering Laboratory, and many others
ASGS ADCIRC Surge Guidance SystemPredictive tool for stormsUsed in conjunction with SLOSH
Modeling with adcircStorm surge height is not directly related to windspeed
Surge can not be predicted from category of storm alone
Hurricane Camille (1969)Category 5In 2005, residents who were safe from Camille did not evacuate for Katrina (category 3)Katrina had a much more severe surge
Modeling with AdcircWind forcingCauses water in front of the storm to pile up on its selfAtmospheric pressureSurface water exposed to low pressure will rise0.39 inches rise in sea level per 1 millibar drop in pressureCurrentsEnergy of a breaking wave exponentially related to current
Modeling with adcircRainfallIncreases riverine flow which increases water depth at outletsBathymetry Shallower waters by the coast cause higher surgeLIDAR advanced modelingTidal dynamicsHigh or low tideWet or dry shorelineIke made landfall at high tide
Case Study: The Ike dikeADCIRC applicationsEvacuation planningPotential damage assesmentProposed structural mitigation testing
The Ike DikeDike proposed to reduce storm surge post hurricane IkeUsed ADCIRC to develop and test
Case Study: Ike Dike
Path of hurricane Ike along with storm surge elevationABCDCase Study: Ike Dike
Landfall point scenarios for evaluationCase study: Ike Dike
Ike path and worst-case Ike pathCase Study: Ike Dike
Original storm surge elevation Projected storm surge elevation Case Study: Ike dike
Storm surge elevation without Ike DikeStorm surge elevation with Ike Dike