USA: Super-size it: Regional storm surge strategy for Houston based on high performance computing (part 2 of 2)

Initially, the SSPEED team studied historical storms to establish baseline storm surges.  A reasonable worst case hurricane track was identified as making landfall on the west end of Galveston Island.  With this track, the highest storm surge would be directed at Galveston Bay and the Houston Ship Channel.  The results of Dawson’s ADCIRC+SWAN modeling were startling, showing a storm surge of 23-24 feet on the west side of the bay and almost 25 feet in the ship channel due to the funneling effect of the bay.  A 25-foot surge would cause significant damage to the petrochemical complex, the ship channel, and western Galveston Bay population centers. 

As a result of this research, the SSPEED Center developed a storm surge mitigation strategy called the Galveston Bay Park/Mid-Bay Alternative and then modeled it with ADCIRC+SWAN to see how effective it would be.  The Mid-Bay alternative consists of an in-bay berm system that generally runs along the ship channel, gate structures for small craft, a large navigation gate for ship traffic, and levees and elevated roads.  Dawson’s ADCIRC+SWAN supercomputer modeling revealed that western Galveston Bay and the ship channel would be much more protected from storm surge with the Mid-Bay Alternative in place, than without it.

To complicate matters, storm surge and inland flooding can happen at the same time during a hurricane.  This occurs when inland (freshwater) flooding, traveling downriver to the coast, meets storm surge (saltwater) being pushed upriver by a hurricane.  When these events happen at the same time, it’s called compound flooding.  Compound flooding has two components that amplify each other and make the flooding worse:  freshwater flooding piles up on the land and can’t drain into the ocean because it’s blocked by salt water storm surge coming inland.  Low-lying coastal regions like the Houston-Galveston area are particularly vulnerable to compound flooding because the land is very flat and drains slowly under normal conditions.  Hurricane Harvey’s mild three-foot storm surge made it harder than normal for the region’s bayous to drain the tremendous amounts of water that fell inland.  But fortunately, the storm surge did not cause devastating impacts like Hurricane Ike’s storm surge on Bolivar Peninsula in 2008.  Very little research has occurred on compound flooding in the US and little is known about how it happens in the Houston-Galveston area. 

The SSPEED Center’s storm surge modeling is helping advance knowledge of our region’s complex hydrology.  This type of complicated research can only occur on supercomputers.  Development of a regional HPC-based flood alert system would provide a foundation for complicated HPC research about coastal storm surge and compound flooding in the Houston-Galveston area.  Improving our regional flood resilience starts with increasing our regional understanding of hydrology—how individual watersheds work, how inland flooding occurs, how storm surge behaves at the coast, and how compound flooding puts coastal residents at increased risk.  Armed with a better understanding of the science, we can be better prepared for floods and hurricanes.  Increasing our knowledge of regional hydrologic systems with supercomputing is vital to improving Houston’s flood resilience.