What Hurricane Ida Teaches Us about Infrastructure
Tulane’s Mead Allison tells John future coastal urban protection will have to be both built and natural
I stayed in New Orleans for the landfall of Hurricane Ida — and I was impressed by the power of the storm, which didn’t flood the city as Katrina did but still knocked out electricity to more than 1 million people. But I’m new to the area and to hurricanes, so I turned to an expert — Mead Allison, professor and chair of the Department of River-Coastal Science and Engineering in Tulane University’s School of Science & Engineering — to explain why Ida, a Category 5 storm, caused less damage to the region than Katrina, a Category 3 storm. I also wanted Mead to explain what the quick succession of powerful storms last year and this might be doing to the region’s coastal ecosystems — and how it might prepare all of its infrastructure to better withstand the next big hurricanes.
John Sabo: This is the third Cat 3–5 hurricane to make landfall in Louisiana in the last year — the other two were Laura and Zeta in August and November of 2020. The normal frequency of such landfalls is once every decade. What have these multiple landfalls done to coastal ecosystems — what are some of the damages? And can these ecosystems recover?
Mead Allison: I might divide the question into aqueous (estuaries, coastal lakes, inner continental shelf, etc.) and wetland (marsh and cypress swamp) ecosystems and barrier island/beach environments.
The aqueous ecosystems are quite resilient and I have not seen anything published on deleterious effects of hurricanes on these systems to food webs or morphology. One exception would be the cascading effects of hurricanes causing breaks in oil pipelines, well heads or rigs. Early reports seem to indicate several oil leaks from broken well heads on the shelf off the Mississippi Delta in Ida. Of course, we are all familiar with the Macondo-BP spill and the massive ecosystem damage it caused.
Wetland ecosystems are sensitive to these events mainly through land loss and saline intrusion. I can recall being in marshes in the birdsfoot delta only a couple weeks after Hurricane Katrina in 2005. Other than wrack lines 3–4 m up remaining human infrastructure like power poles, you could not recognize that the marshes had just experienced massive flooding and wave action while submerged. Wetland edges however are pounded by large waves in both the waxing and waning phases of storms prior to submergence and past history has shown extreme rates of wetland loss by shoreline retreat in big storms. The movement inland of all that material ripped up from wetland edges can cover marshes further inland forcing regrowth of the system.
The biggest “win” in Ida is the performance of the new $15 billion flood protection system around metropolitan New Orleans built post-Katrina. This system of floodwalls, levees, pumping station and flood gates known as HSDRRS (Hurricane and Storm Damage Risk Reduction System) performed magnificently in its first severe test, halting storm surge from entering the city.
— Mead Allison
Katrina also showed that mineral poor, organic-rich surficial marsh substrates can be ripped up wholesale like cutting turf for new lawn making. Sometimes the underlying substrate regrows post-storm, and sometimes not.
Finally, Louisiana wetlands are roughly arranged in belts from saline marshes closest to the Gulf, through brackish and then freshwater marshes further inland, and finally freshwater cypress swamps in the highest, most inland locations. Past storms have caused large-scale kills of cypress and other species that are salt intolerant leaving “skeleton forests” that can be seen throughout the delta today. This is the harbinger of inland migration of coastal environments — cypress is typically replaced by marshes. Of course, in this time of human acceleration of sea level rise and storm frequency/intensity, its not clear how this “natural” migration of coastal environments will proceed, particularly since upland boundaries of wetlands are typically up against places where we live.
Louisiana’s barrier islands and beaches have been battered by previous storms that cause beach erosion, migration inland with overwash, and damage to floral and faunal communities. Our barriers are particularly vulnerable due to their limited sand supply (they are disconnected from longshore transport of sand from adjacent beaches since they were created by deltaic processes) and they are sinking due to our high subsidence rates that compound sea level rise. Many have melted away and sunk below the waves in the historical period, which exposes the coastal estuaries they protect to even more wave damage during hurricanes.
John Sabo: Ida was rated a more powerful storm, but Katrina was more damaging, at least in terms of preliminary dollar estimates. How are we to understand that? What are the factors that determine how damaging a storm can be?
Mead Allison: Each hurricane is an individual with characteristics beyond just wind speed that impact damages — overall size of the storm impacts the size of the severe wind field, angle and speed of approach to the coast, density of human infrastructure in the path, and antecedent storm history (Katrina was a Cat 5 several days before landfall and still had a storm surge to match) all play a role.
Then there are the economic factors.
Damages can be divided into wind and water damage — in fact most coastal residents in the Gulf have separate wind and flood insurance and there is often an argument between insurance companies and homeowners after a storm about whether damage was caused by wind or surge. This is the key to understanding the differences between Katrina and Ida. Despite the fact that New Orleans was on the “strong side” of the storm in Ida and the weak in Katrina, damages were more severe in the metro area in Katrina. That can be ascribed to the failing levees, destruction of the pumping system to remove water, and 80% of the city ultimately sitting flooded for several weeks after the storm. Water damages were catastrophic and extended to tens of thousands of structures.
Wind damage was relatively light with the exception of the Lake Pontchartrain waterfront which was closer to the eye and had unrestricted wind field.
Despite the fact that New Orleans was on the “strong side” of the storm in Ida and the weak in Katrina, damages were more severe in the metro area in Katrina. That can be ascribed to the failing levees, destruction of the pumping system to remove water, and 80% of the city ultimately sitting flooded for several weeks after the storm.
— Mead Allison
The biggest “win” in Ida is the performance of the new $15 billion flood protection system around metropolitan New Orleans built post-Katrina. This system of floodwalls, levees, pumping station and flood gates known as HSDRRS (Hurricane and Storm Damage Risk Reduction System) performed magnificently in its first severe test, halting storm surge from entering the city. While a direct hit from Ida would have been likely above the standards to which it is built (1 in 100 year storm), it is designed to be overtopped not collapse as the old system did, which would have lessened flood damages even in that extreme scenario.
Wind damages in Ida were more severe than in Katrina but still don’t come close to the massive dollar damages in New Orleans caused by the flooding. Outside of the flood protection system around New Orleans, and another in the bullseye of Ida along the Highway 1 corridor from Raceland to Golden Meadow that leads to the massive oil/gas port at Port Fourchon, the damages from water (surge) and wind were catastrophic.
However, there is a lesson to be learned from the metro New Orleans Ida experience. Coastal cities like New Orleans, Houston, Miami and New York that are vulnerable to rising sea levels and increasing tropical storm frequencies, are considering strategies of gray infrastructure flood protection (HSDRRS-type). These require bringing power in from outside the flood walls to maintain pumping from extreme rainfalls inside the walls and to keep power to our homes. All the transmission lines into New Orleans were cut during Ida, which was as effective in shutting down the city for weeks after the storm as Katrina’s flooding was. Integrating power into future planning for coastal city flood protection will be vital.
Also, cities disconnected from surrounding coastal ecosystems that are battered by these storms are subject to increasing surges in storms (from less damping of energy by a “nature belt”) and loss of ecosystem services, that, in Louisiana, includes jobs in a variety of industries including seafood and tourism. Future coastal urban protection will have to pursue a combined gray-green protection strategy in my opinion.
John Sabo: This storm has had far more repercussions for energy infrastructure than water infrastructure. What are your takeaways about the relative vulnerability of these ) infrastructures — and how the region might better prepare for the next big hurricanes?
In Louisiana “energy infrastructure” includes not just the power grid but the massive infrastructure built around extracting hydrocarbons from the Gulf (rigs and coastal ports to service), getting them to market through pipelines that criss-cross the shelf and coastal wetlands and inland water bodies, and petrochemical industries that line the Mississippi River corridor.
However, there is a lesson to be learned from the metro New Orleans Ida experience. Coastal cities like New Orleans, Houston, Miami and New York that are vulnerable to rising sea levels and increasing tropical storm frequencies, are considering strategies of gray infrastructure flood protection (HSDRRS-type). These require bringing power in from outside the flood walls to maintain pumping from extreme rainfalls inside the walls and to keep power to our homes.
— Mead Allison
The State of Louisiana’s Master Plan for coastal restoration and protection puts a priority on planning for maximum resilience for human populations and coastal ecosystems — not industries. Industries do not always have the finances to individually protect, but we, as citizenry have to have it. Damages to this energy infrastructure impacts jobs locally and supply chains for hydrocarbons across the nation.
Also, oil spills from pipelines, storage tank farms, offshore rigs and refineries, which have already happened in hurricanes, have huge consequences for people and ecosystems. Hardening or moving and, longer term, reducing reliance on hydrocarbons, will be key in my opinion.