How New Orleans, the sinking city, fights rising tides
Marie Donlon | March 22, 2023When Hurricane Katrina made landfall as a category 5 hurricane back in August of 2005, New Orleans and other surrounding regions were devastated. According to estimates, 80% of the city was flooded for weeks following the storm.
The reason for such devastation is reportedly due to engineering flaws in the city’s aging flood protection defense network of floodgates and levees, the result of which was an estimated 1,400 fatalities and damages estimated to be in the billions of dollars.
Specifically, the levees and floodgates surrounding the city were breached as a result of a poorly maintained protection system, with blame mostly falling on the U.S. Army Corp of Engineers, the government agency that had designed and built the levees decades prior to the hurricane. According to several reports, some levees, which are embankments or walls composed of Earth that run parallel to rivers, experienced erosion of their backslopes over time. Meanwhile, some of the city’s floodgates — gates that open and close to admit or exclude water — were either poorly constructed or inadequately maintained.
As such, many efforts have been made to prevent future failures and flooding in the event of another Katrina-like — or worse — scenario in a city already vulnerable to both sinking and flooding due to its location in a shallow bowl that sits just below sea level between the Gulf Coast and the Mississippi River.
The Hurricane and Storm Damage Risk Reduction System (HSDRRS)
Following the damage from Hurricane Katrina, the Hurricane and Storm Damage Risk Reduction System (HSDRRS) was enacted for five Louisiana parishes (Orleans, Jefferson, St. Bernard, St. Charles and Plaquemines). According to its developers, the HSDRRS flood protection system is composed of 350 miles of fortified levees and floodwalls, 73 non-Federal pumping stations, three canal closure structures with pumps and four gated outlets. This system was designed to halt rising sea levels and flooding from Katrina-like storms.
Distinguishing the HSDRRS project from earlier flood defense systems in the city, which is virtually surrounded by water, was the construction of higher, more resilient levees and flood walls as well as canals and pumping stations.
Pumps
Once considered a modern marvel of engineering, New Orleans' system of pumps, which moves water out and over higher land, dates back to the 1910s, and many of those same pumps are still in use today, according to reports. Canals throughout the city carry pumped water from pumping station to pumping station all the way to the end of the line and ultimately into one of the city’s surrounding lakes including Lake Borgne and Lake Pontchartrain.
In addition to the constant duty pump and a screw pump, both of which are still in use from the 1910s and located at the city’s Drainage Pumping Station No.1, new pumping stations and even so-called “monster pumps” have been installed throughout the city in the years following Katrina.
Further, emergency pumps and canal closures have also been installed at the ends of the outfall canals as part of the HSDRRS project.
For more on some of the pumps currently in use in New Orleans, watch the accompanying video that appears courtesy of NOLA.com.
Levees and floodgates
Much of the blame for the catastrophic failure of the existing flood defense system in place during Katrina has been laid on the levees and floodgates throughout New Orleans. With reports suggesting that some levees were too low, while others were either poorly designed, maintained or constructed, water was able to infiltrate the city, unchecked. Now, those levees and floodgates have been rebuilt and strengthened under the HSDRRS project.
The new HSDRRS barrier system of levees and floodgates, which proved effective against Hurricane Ida, a category 4 hurricane that made landfall in 2021, was created based on data collected about their respective performances during a handful of storms and hurricanes. Using that data, the project researchers employed computer modeling to design improvements to the floodgates and barriers.
For more information on the levees and floodgates protecting New Orleans, watch the accompanying video that appears courtesy of the University of Washington.
Green infrastructure
While most of the efforts in place to protect against Katrina-like flood waters were made to existing infrastructure, some efforts are exploring new and greener methods for staving off flooding. For instance, the Urban Conservancy, a New Orleans nonprofit that offers resources associated with environmental stewardship, is attempting to improve urban drainage under its Umbrella project, which seeks to make communities in the New Orleans more flood resilient through “small but meaningful acts,” as its mission statement suggests.
The project, which aims to incorporate green infrastructure on the residential level, seeks to use native plants as part of an improved drainage system as well as rain gardens, barrels, planters, trees and permeable pavement to construct so-called green streets in regions of the city overwhelmed with non-permeable concrete. Such small measures, according to the Urban Conservancy, are expected to reduce the pressure on pipe and pump networks running throughout New Orleans and, ultimately, slow the flow of water.
Coastline restoration
Coastlines the world over are experiencing significant erosion. As such, one proposed method for preventing flooding and thus sinking in a city hard hit by flooding is to rebuild or fortify coastlines. Consequently, there are many efforts underway to fortify coastlines and protect against erosion using sand dredged from the floor of waterways. Unfortunately, dredging for sand intensifies coastal erosion.
As such, a New Orleans’ nonprofit dubbed Glass Half Full collects the city’s glass and recycles it, transforming it into sand and glass cullet for coastal restoration, eco-construction and more.
The nonprofit collects glass waste, sorts it by color and removes other material like plastic and then processes the glass using hammer mill crushers.
Restoring coastlines would require hundreds of thousands of cubic yards of sand amid a global sand shortage. However, Glass Half Full pulverizes recycled glass into a soft sand-like substance for rebuilding those coastlines in a sustainable approach.
These are just a few of the efforts employed in the years following Katrina to protect the sinking city amid rising tides. Check back with GlobalSpec for more on this and other engineering topics.
Maybe it's time to return New Orleans to Mother Nature? She's going to win, one way or the other.