NEW ORLEANS – Today, the Sewerage & Water Board of New Orleans (SWBNO) released the findings of the Southeast Louisiana Urban Flood Control program (SELA) impact study conducted by Ardurra, a third-party contractor.
Prompted by flooding on July 10, 2019, Mayor Cantrell and SWBNO tasked Ardurra with fully analyzing the impact drainage improvements under (SELA) had on mitigating flooding. Both the Mayor and SWBNO recognized the public’s concern surrounding the impact of the SELA program as large parts of Uptown, where the most recent SELA underground canals were installed, were inundated with stormwater.
“This report is an example of our commitment to being transparent about how our system works,” said Ghassan Korban, Executive Director, SWBNO. “As a public utility, it is our responsibility to hear the concerns of those we serve. That is why Mayor Cantrell and I called for this thorough, third-party analysis. I hope these findings help inform the public of the impact of the SELA improvements while shedding light on how our system handles these more intense rainstorms.”
“We take the safety, wellbeing, and trust of our residents very seriously, and we understand that the flooding has taken a toll on our people,” said Mayor Cantrell. “It was important to have Ardurra conduct this study to ensure that the SELA project is doing what it supposed to do. With the contributions of SELA, we are seeing the reduction of flooding around the city. This is a great step forward, but there is still work to be done. I am proud of the work and improvements at the Sewerage & Water Board in conjunction with the Department of Public Works and the Army Corp of Engineers. Our infrastructure & drainage system is a shared responsibility and we have all been seamlessly working together.”
SWBNO specifically asked Ardurra to create a digital model of the July 10 rain event. Ardurra overlaid rainfall data – intensity and volume per location specific to the city blocks – with the designed capacities of SWBNO’s drainage canals, pump stations and large culverts.
Here are some highlights of their findings:
The model used accurately simulated the July 10 rain event – the result of more than eight inches of rain falling in three hours in some areas.
- The rainfall on July 10 in some blocks reached a volume and intensity of a storm that had less than a 1 percent chance of happening in any given year. In other words, some neighborhoods saw rain that surpassed that of a 100-year storm.
- The SELA canals installed under Uptown streets held and conveyed the expected amount of stormwater as designed.
- SELA did not contribute to flooding in other areas. The drainage system downstream from the SELA canals had been expanded in the 1980s and 1990s to manage a storm event in similar fashion to SELA’s design.
- Uptown SELA improvements do not drain Mid-City or downtown, where separate canal networks convey water to different pump stations. Therefore, it is impossible for SELA improvements to have in impact on flooding in Mid-City and downtown.
The SELA analysis is the latest step taken by the Cantrell Administration and SWBNO to methodically investigate the limits of New Orleans’ drainage system. Inspecting underground canals, cleaning clogged catch basins and identifying trouble spots for street flooding are all building blocks toward a master plan to re-envision stormwater management in the City.
The full study can be found here.