As a tropical system approaches the coastline and the intensity and impact of the storm becomes evident, officials and first responders brace for landfall by staging equipment and readying personnel for the aftermath. To assist in these efforts, researchers at the U.S. Army Engineer Research and Development Center use numerical modeling systems to help U.S. Army Corps of Engineers districts better prepare for storms.
The Advanced Circulation model is a higher-order accurate, physics-based and highly parallelized computational model. It is the USACE’s Hydrology, Hydraulics and Coastal Community of Practice preferred model for storm surge and circulation and is considered the industry standard for use.
Earlier this year, as Hurricane Laura approached the gulf coast, the National Oceanic and Atmospheric Administration’s National Hurricane Center began narrowing landfall predictions along the border between Texas and Louisiana. As some of the region fell within the USACE Galveston District’s area of responsibility, they immediately began preparing for the storm.
“We were contacted by the Galveston District through the USACE Reachback Operational Center and asked specifically to run some scenarios for them that would look at the structures they’re in charge of maintaining and operating to see what kind of impacts they could expect,” said Chris Massey, a research mathematician at the ERDC’s Coastal and Hydraulics Laboratory. “Specifically, they wanted us to run the consensus track from the NHC.”
Beginning with the NHC’s Advisory 23, CHL began storm surge simulations of Hurricane Laura making use of the ADCIRC mesh for the coast of Texas. That mesh has over 4.5 million nodes and over 8.9 million unstructured triangular elements with element sizes down to 20 meters in some key inland locations.
The ADCIRC model simulations use forcing values from tides, along with wind and surface level atmospheric pressure fields. The wind and pressure time series fields were derived from the NHC forecast advisories and computed by ADCIRC using its internal asymmetric cyclone vortex model.
“We worked with some of our partners at Louisiana State University, the University of Georgia and the Coastal Prediction Restoration Authority in Louisiana to get those winds and pressures,” Massey said. “They have an automated method for generating the necessary wind and pressure field input decks for the model. They were very gracious partners and let us have that setup to get us going to help the district.”
Once they had the consensus track, Massey and his team were able to edit it to alter the track location and the intensity of the storm for several different scenarios to see the impact on district assets.
“By that evening, we had three scenarios simulated with the results handed back over to the district for them to review,” Massey said. “We provided both some static images that showed what the maximum water levels would be, and then we also provided raw data files for them so that they could bring in their Geographic Information Systems with their GIS experts.”
“From the district’s perspective, this is very much operational support,” he added. “They are looking at gate operations, or places that might be potentially compromised during an event, so that they can start to plan and monitor and get things in place — it helps fill in their picture.”
The NHC’s mission is to save lives, mitigate property loss and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather and by increasing understanding of these hazards. For ERDC and the USACE, the main goal of the ADCIRC model is to augment the information provided by the hurricane center with additional data, providing USACE districts and local partners the ability to make more informed decisions regarding operational structures and support.
“The model allows us to answer questions like when will the highest water levels be coming in, when will that water level get to a threshold height and how long will it be at that height,” Massey said.
“The Galveston District used the ERDC-produced ADCIRC scenarios to make informed operational recommendations to our partners on which areas are safe to position personnel and equipment and where to reposition our assets,” said Coraggio Maglio, Hydraulics and Hydrology branch chief at the Galveston District. “A 30-mile western shift in the hurricane’s landfall location would have had very different consequences for our region. When looking at overtopping scenarios for leveed areas, a single additional foot in total stormwater level can be a significant consideration.”
“The ADCIRC capabilities are important for all of our districts when they are planning operations and responses, because the model allows us to potentially shore up areas that may have been weakened,” Massey said. “It helps with planning, which can prevent further disaster, or positioning of resources for use after the fact.”
“The ability to provide this data to the officials in East Texas was vital during Hurricane Laura,” said Alicia Rea, Galveston District director of Emergency Management and Security. “Our district Commander Col. Tim Vail rode out the storm in Orange, Texas, with local officials at the Orange County Emergency Operations Center. He was able to provide our data in real time, which allowed the local officials to make quick and effective decisions. The work our team did during Laura will help foster our relationships along the Texas Coast well into the future.”
“This modelling effort really just supports the mission of the USACE in terms of flood risk management for the communities,” Massey said. “ERDC is here to bring our expertise to help our districts during this kind of situation ⸺ that’s the purpose of the UROC. We are here to support the operational needs of our districts for specific scenarios that involve specific district interests.”