Water Level Loggers Track Hurricane Surge in the Nick of Time
Shortly before Hurricane Rita came barreling onto the Louisiana coast in late September, a group of hydrologists from the U.S. Geological Survey (USGS) in Ruston, LA came upon a novel idea as to how they might be able to track storm surge levels as the hurricane was happening.
The idea was to deploy water level data loggers, which were typically used for groundwater monitoring, in areas throughout coastal Louisiana and Texas that were likely to be inundated by the surge.
"Ever since the USGS has been in existence in Louisiana, we've always tried to document the effects of hurricanes on the Louisiana coast," said Ben McGee, a supervisory hydrologist with the USGS. "Up to this point, storm surge data had always been generated after the storm. We'd basically go into a storm-impacted area after the fact and look for high water marks that indicate storm surge. After Hurricane Katrina, a group of us here in Ruston were lamenting the fact that we couldn't be more proactive about data collection in the face of major hurricanes. We kicked around some ideas, and started thinking about putting out recording devices."
A number of federal and private agencies are interested in storm surge level data for various reasons. For example, FEMA is interested in storm surge elevation data, which is used for flood zone labeling and building codes. The USGS is interested in the data for scientific purposes, such as understanding the water quality effects of storm surge and its effect on ecosystems. And, the impacted states and cities are interested in the data because it ties into funding for relief, and making decisions in terms of where to rebuild.
The group's concept quickly turned into reality. Within a 72-hour period, McGee and his team obtained approval and funding from USGS for the proposed monitoring project, purchased and received 46 HOBO® water level data loggers from Massachusetts-based Onset, and rushed down to the Louisiana coast 250 miles away to put their plan into action.
There, the team spent a stormy, pitch-black night attaching the loggers to pilings, bridges, and other structures throughout coastal Louisiana that would survive the hurricane.
"Once we identified the instrumentation we needed, we had to act fast," explains McGee. "It was September 20th, and the hurricane was supposed to make landfall a few days later. We ordered the data loggers on September 21st, and we knew it would take a day to get them in. In the meantime, we were building protective housings for all the loggers, getting our sampling plan together, and just scrambling around the clock to get everything together. We went to the local UPS office to basically get the loggers off the truck on the morning of the 22nd and left our Ruston office at one p.m. for the coast."
To determine the monitoring coverage area, the team had analyzed a digital elevation model and plotted the areas where the hurricane was expected to make landfall. The coverage area turned out to be approximately 4,000 square miles, from the Beaumont/Port Arthur area in Texas to Lafayette, Louisiana. According to McGee, the size of the monitoring area forced the team to seek out an economical data logging solution that would enable the greatest number of monitoring points for the given budget.
Even though McGee's use of HOBO loggers does not imply endorsement by the USGS, he describes the decision to use the devices in this manner: "To get adequate coverage, we figured we needed about 50 monitoring sites. The price of the HOBO loggers was about half the cost of other units we checked. They didn't have some of the bells and whistles of some of the others, but those were features we didn't really need to get the job done. A more expensive solution would not have given us the coverage we felt we needed."
The loggers were set up on laptops running HOBOware® software, and programmed to measure and record water levels every 30 seconds around the clock. The protective housings were constructed out of 1.25" O.D. steel pipe.
Once the loggers were ready for deployment, McGee and others worked through the night securing the loggers to hurricane-proof structures.
"I remember being on Sabine Lake at midnight, and Hurricane Rita was several miles offshore," said McGee. "Standing waves of water were being pushed into the lake at 4 to 6 feet per second. It was a very dark night so we had to work with headlamps. It was quite a sight."
Once all the loggers were deployed, it was Friday afternoon and the team abandoned the area and drove back to Ruston. Hurricane Rita slammed into the coast early Saturday morning.
"We basically got everything done in the nick of time," said McGee. "It was very intense."
One week later, the effort to recover the loggers began. Approximately 80% of the loggers were recovered, and the team is currently in the process of offloading and analyzing the data.
"A database is being built to house all of the data we collected, and by displaying the data in a time-series manner, USGS scientists will get a visual sense for the flood inundation as reported by the loggers,” said McGee.