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