Lafourche native Dr. Windell Curole is a nationally recognized hurricane and levee expert who has served as General Manager and Executive Secretary of the South Lafourche Levee District for over 40 years.
He will discuss a report – issued in the wake of 2021’s Hurricane Ida – on the efforts of local governments to provide flood protection based on lessons learned from Hurricane Katrina.
The document is titled: “Report on Challenges to Coastal Communities in Louisiana.”
KATRINA PROBLEMS, IDA SOLUTIONS
Hurricane Katrina Landfall, August 29, 2005
Hurricane Ida Landfall, August 29, 2021
The South Lafourche Levee District studied the effect that Hurricane Katrina’s storm surge had on flood protection projects in New Orleans, St. Bernard, and Plaquemines. The District found that the flood protection projects in St. Bernard and Plaquemines were overwhelmed by the height of the storm surge. The issues in New Orleans were not the levees, but the floodwalls that failed to protect the city. The I-walls along drainage canals had structural problems which lead to breeches in the walls at 17th Street Canal and London Avenue Canal.
After assessing these issues and the need for more dependable funding, the Levee District’s board proposed to the public and received a one-penny sales tax to add to the 9.68 mill property tax already being collected in South Lafourche. With critical, but sporadic funding assistance from the Federal and State governments, and a steady yearly stream of local tax money, the Board proceeded to increase the height of the local levee system by five feet. The Board also supported the Corps’ recommendation to construct H-beam supported I-walls. The last improvement instituted by the Board was to harden the intersection of levees with I-walls. The Board also concluded there was no need to alter the basic design of levees except for more elevation.
All this work became much more efficient due to the accuracy and economy of the GPS based elevations which became available to the District in 2004. This groundbreaking technology correctly identified and measured that the hurricane levee system was 18 inches lower than designed. Armed with accurate, detailed elevations, it became easy to identify and improve low areas on the levee, and to accurately raise the height of those levees. This was the last piece of the puzzle which allowed a positive outcome when Hurricane Ida hit.
An understanding of the performance of the system may be described best by the comments of engineers who work extensively in south Louisiana. The following comments and report were provided by Jason Kennedy and Stephen Bourg.
Jason Kennedy, Delta Coast Consultants
“As far as storm track and intensity, it is hard to imagine a more “worse-case” event for the South Lafourche system than what occurred for Hurricane Ida. One of the greatest success stories that I have seen, from a flood-protection standpoint, was the ability of the SLLD flood protection system to withstand and weather the storm surge from Hurricane Ida. Zero homes or businesses were flooded from this event, which is simply remarkable given a storm surge of 12-15’ with significant wave runup in addition to that. This event far exceeded the criteria for which this system was originally designed, yet it still worked flawlessly. The success of the SLLD system is a great template for Morganza to the Gulf. It is a shining example of the relentless construction program that must be implemented in order to protect our vulnerable coastal communities against the ever-increasing intensity and frequency of these tropical systems.”
Stephen C. Bourg, PE, SR VP, All South Consulting Engineers, LLC
I just wanted to provide you with some positive and unexpected observations that I took away from our recent inspection ride of SLLD’s levee system on September 23, 2021 regarding the impacts from Hurricane Ida.
First off, I was really expecting to see a much different outcome of our site inspection than what was observed. As you are aware, I am very familiar with hurricane damages to levee systems and previously have witnessed, inspected and repaired several levee systems in the immediate aftermath of major Hurricanes. I have 28 years of flood protection experience working for numerous levee districts, CPRA and USACE. After Hurricane Katrina, I personally inspected and preformed emergency repairs for the USACE for the New Orleans East Levees, Industrial Canal and Outfall Canal Floodwalls which were decimated by the storm surge and wave action. After Hurricane Gustav, Ike and again for Isaac I performed levee inspections and emergency repairs for Plaquemines Parish Government on their 23 miles of non-federal back levees which were significantly overtopped due to insufficient elevation which resulted in majors levee breeches and widespread flooding for all 3 events.
So, I was aware that SLLD’s levee system was not breached by Hurricane Ida but was expecting similar levee scour damages to what I previously witnessed for Hurricane Katrina, Gustav and Isaac. What I observed was totally different than what was expected and want to provide you with a few positive observations that I took away from our recent inspection:
- SLLD’s system is truly a system and performed outstanding to the impacts of Hurricane Ida’s direct impacts. I say this because the levee system had an almost uniform freeboard throughout SLLD’s levee system. From the north end of the system at El 12.0 to the southern end at El 18.0 the debris lines and high-water marks were almost uniform in height relative to the levee crown. So, the levee heights throughout the entire system were dead on. SLLD utilized its levee funding wisely in the correct locations.
- A significant amount of your levees did overtop by appeared to be only minimal from wave action. This was concluded by significant amounts of debris rested on the protected side slopes and berms, the levee protected side slopes faired well with minimal damage except for one small reach of levee on the east side.
- The toe sheeting and rip-rap that was installed on the open water sections of the flood side berm toes protected the berms and levee section in these critical areas. This added protection saved the levee in these areas.
- The fronting protections / non earthen sections at several of the pump stations overtopped, however; no major structural failures were observed. It appeared that some of the original walls were recently increased in height by nontypical flood protection standards. These cost-effective height increases at the floodwalls worked for this event. This prevented significant overtopping.
- The areas with the wider levee crowns had more debris collection (and debris depth) and less damage to the levee section. So the wider levee crowns helped the overall system and minimized additional overtopping / scour due to wave action.
- The flood side levee slopes that could be observed did take a beating with the grass / turf removed but it was difficult to determine in most areas due to the significant and unprecedented amount of debris.
- I am aware that SLLD’s Levees have a higher organic content and higher % of debris than the USACE standards allows but even with these lesser standards the levee surface and turf did not fully deteriorate under the overtopping conditions. The high shell content within the levee section can be observed throughout due to the scour / turf removal but the levee sections held up well in the overtopping areas.
- Again, I believe that the recent increased height lifts prevented this levee from significant surface erosion and deterioration – so elevation appears to be a more critical factor than material type, compaction requirements and stability factors of safety
- The system is only as good as the weakest link-so it’s very import to fully understand the effect of every hurricane event so you can continually improve on the reliability of your levee system.
- The amount and types of debris on the levee is like no other storm that I’ve inspected. From the amount of mixed marsh grass / construction and demolition debris on the west side to the amount and depth of marsh grass on the northeast side. The marsh was relocated to the levee slopes and berms on this east side by Cloverly Farms with a major root ball under the grass – 80% mud / root ball with the marsh still actively growing on the levee footprint.
- The pre-storm marsh adjacent to the levee system has been significantly disturbed /destroyed due to the storm wave action and surge. These additional open water areas will worsen the effects to the levee for future storm events. Additional flood side toe scour protection is going to be needed along the toe of the levee system for a much greater length.
- At locations where the flood side levee toe had shrubbery or minimal tree lines, the levee flood side surface scour and deposited debris was significantly less. A ridge adjacent to the flood side toe is an important feature to protect the levee system during these major events. This needs to be investigated further and this feature contributed to the success of your levee system.
- The overall quantity of debris is unprecedented and estimated at 1 million cubic yards on the maintained levee footprint. There are significant amounts of additional debris just outside of your maintained levee section which could impact your levee in the future. I have never witnessed this amount of debris on a levee system. Hurricane Ida produced much more debris on a levee system than witnessed after hurricanes Katrina, Rita, Gustav, Ike and Isaac.
- Additionally, the heavy levee marsh grass debris 4’-5’ in thickness (majority an 80% root ball) will provide additional consolidation to the flood side berms and cause settlement which will require additional clay material. This debris needs to be removed immediately to minimize further damage.
- As you are aware, we are looking at several alternate means to dispose of this debris-load haul, burning marsh grass, composting on the protected side levee berms. It is anticipated we will be using a combination of all 3 methods to efficiently and cost effectively rid this debris.
- So, in conclusion, the major observation that I took away with in my inspection is the levee crown elevation is most critical. It is my opinion that the levee crown elevation is key over the other levee characteristics / factors to which prevent major overtopping which then results in major failure. The elevation of SLLD’s levee system saved South Lafourche.”
The actions taken by the South Lafourche Levee District in the years between Hurricane Katrina and Hurricane Ida were critical to the success against Ida’s storm surge. The actions which led to success can be duplicated by other levee systems in coastal Louisiana.
Windell A. Curole
South Lafourche Levee District
Cell: (985) 632-7554