When staff at the Geological Survey Water Resources Division in Ruston returned to their homes after documenting flood levels from Hurricane Katrina in 2005, they decided there had to be a better way to calculate storm surge.
Until Katrina, gathering information about where storm surge went and how high the water got was done by looking for watermarks on buildings, said Ben McGee, supervisory hydrologist with USGS.
Staff started talking about how to gather information in a more proactive way and decided they could deploy sensors normally used for groundwater studies before a storm hit. These sensors would then take measurements as storm surge rolled in and after the storm, McGee said.
Staffers got approval for additional funding, and by the time Hurricane Rita churned in the Gulf of Mexico a few weeks after Katrina, they were ready to deploy their first set of sensors, he said.
Since then, the rule has been to deploy the sensors on the first storm that hits the shore of the season and for any Category 3 or greater hurricane after that, McGee said.
Since 2005, the crews have gone out seven times and deployed five sets of sensors, he said. During Hurricane Isaac, crews from multiple states put out 160 sensors in southeast Louisiana and southwest Mississippi and have since collected all but three of them, which are still underwater in Plaquemines Parish, he said.
There were 12 of these sensors that sent back information every 30 seconds while the rest of the sensors need to be collected and analyzed.
One thing the sensors have shown is that, in general, high water marks are usually lower than the actual high water that occurred in the area, McGee said.
“The peak (of high water) may only occur for a short period of time before it recedes,” McGee explained.
That short period of time may not be long enough to make a water mark on a structure, he said.
“There are a lot of things a high water mark can’t tell you,” McGee said.
The water mark can tell you when the water arrived, how fast the water rose or when the water receded, he said.
The data sensors that are deployed before a storm can answer those questions and give a better picture of how storm surge moves across an area.
That information can be fed into storm surge computer models used by National Weather Service and others, and help improve storm surge forecasts in the future, said Phil Turnipseed, director of the U.S. Geological Survey National Wetlands Research Center in Lafayette.
“Models are models and they’re no good without data,” Turnipseed said.
In addition, the information can be used by engineers in designing homes or bridges and by flood insurance companies, McGee said.
George Arcement Jr., director of the Louisiana Water Science Center in Baton Rouge, said the USGS was given the job by the Federal Emergency Management Agency to collect the information for flood maps and other efforts.
“Obviously, the data being in the form it is now, modelers are going to love it,” he said. “It’s going to be a ground truthing verification of what actually took place.”
Preliminary information about surge heights and stream heights collected from various sources during the storm are available at http://22.214.171.124/Apps/IsaacStormSurgeMapper/IsaacStormSurgeMapper.html#.