Force of nature: Katrina's legacy

12th October 2012


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  • Ecosystems ,
  • Biodiversity ,
  • Natural resources ,
  • Water ,
  • Pollution & Waste Management



Seven years after New Orleans was devastated by Hurricane Katrina, Suzy Hodgson reports on the environmental impact and legacy

Stranded people stood on rooftops surrounded by torrents of filthy floodwater, debris and bodies, helpless after the terrifying consequences of Hurricane Katrina. These are the horrific images of a flooded New Orleans wrecked by storm surges that will forever be embedded in many people’s memories. With 1,836 lives lost, 275,000 homes destroyed, and a record $90 billion of property damage, the human, social and economic costs were catastrophic and unprecedented.

The hurricane, with wind speeds of up to 175 miles per hour, produced a storm surge that reached 6.7 metres in New Orleans. At least 80% of the city was under floodwater on 31 August 2005, largely as a result of levee failures from the adjacent Lake Pontchartrain. The combination of strong winds, heavy rainfall and storm surges led to breaks in the earthen levee after the storm passed, leaving parts of the city under 6 metres of water.

Water quality

As flood water and storm water covered the majority of the city, setting up multiple sampling and collection sites, as well as actively pumping the storm water into the lake to prevent health risks, was imperative for authorities. In the event, an estimated 100–200 billion litres of floodwater effluent was pumped into Pontchartrain, which acted as the primary dumping ground for the floodwater, amounting to about 2–3% of the volume of the lake.

During the months after the hurricane, the US Geological Survey (USGS), in partnership with the US department of the interior and the Environmental Protection Agency (EPA), undertook continuous monitoring and surveyed samples of water and sediment at regular intervals to compare conditions before and after the hurricane.

For the first year following the storm, water quality remained a significant environmental issue. Now, seven years later, what have become the significant environmental issues?

Surprisingly, the majority of the surveys show that Katrina did not a have an “appreciable negative effect on the ecological health of Lake Pontchartrain”.

The main reason given for the relatively benign impact was the existence of natural continuous flushing and high saline levels, which slowed down the growth of faecal coliform bacteria. Faecal indicators, such as E. coli, measured both in the concentration and the distribution of potential pathogens, did not change the overall water quality.

However, it is important to note that the term “didn’t change” is a relative term for New Orleans. Lake Pontchartrain has long been a dumping ground or sink for New Orleans, receiving all the city’s urban and industrial drainage. After the hurricane, the lake also became the dumping ground for the floodwaters that engulfed the city.

Initial recovery efforts focused on plugging leaks in levees, clearing debris and repairing water and sewer systems. The US Army Corps of Engineers – the federal agency responsible for canal construction – removed tonnes of turbid water, thick with contaminated sediment left behind by receding floodwaters, much of which was dumped into the lake.

Concentration in sediments did not change significantly, remaining at poor levels both before and after the hurricane. Although 10 out of 20 sediment samples contained lead and arsenic that exceeded the drinking-water standard of the EPA, the contamination was generally reported by the USGS as localised and temporal.

Water quality was found to have higher salinity, but within “tolerance levels” of recreational and commercially valued fishing. “Urban” is the operative word. The environmental and ecological problems associated with New Orleans started long before Katrina. The history of development in and around New Orleans had already set the stage for potential disasters.

Industrial heritage

The state of Louisiana is a leading producer of oil and the second most prolific producer of natural gas in the US. Its offshore waters, which include the outer continental shelf, hold the largest reserves of oil and gas in the country. This oil extraction and production comes at a high cost: between 1932 and 2000, Louisiana lost 4,900km2 of coastal land, and a further 56km2 was lost in 2005.

The Port of Louisiana handles one-third of all US natural gas and crude oil production. In the 1960s and 1970s, gas production and extraction accelerated, with associated land subsidence and the destruction of New Orleans wetlands.

New Orleans and its surrounding area are 1.3–3.7 metres below sea level, so a network of seawalls and levees have been built to protect city.

Over the years, heavy metals and volatile organic compounds from industrial agriculture and the petrochemical industries have accumulated in lake sediments. These toxics include arsenic, lead, mercury, chromium and xylene.

At the time of the hurricane, New Orleans was already the location of several “superfund” sites – industrial sites so heavily polluted they were designated as requiring federal clean-up. Five of these sites were flooded along the industrial corridor between New Orleans and Baton Rouge.

Long before Katrina, the Mississippi, once a meandering great river, with natural tributaries and wide floodplains, was converted in the New Orleans area to an intracoastal waterway system.

Over 10 years, the lower Mississippi was canalised with the main spine of the water highway system called the Mississippi River–Gulf Outlet (MRGO) canal, which was completed in the 1960s and provided a shorter route to the port.

In the decade before the MRGO, the central wetlands contained about 32.4km2 of swamp, 30.7km2 of freshwater marsh, 16.2km2 of brackish and salt marsh, and more than 4km2 of forest. The MRGO cut through several natural ridges, funneling salt water into the freshwater ecosystems, where it killed cypress and freshwater marshes. By 1978, only 0.1km2 of forest remained.

Back to nature

These conditions in New Orleans set in motion a larger disaster, not only because of the pollutants associated with oil and gas exploration and production, but also the huge loss of wetlands.

Moreover, local economic conditions did not help. New Orleans is a relatively poor city, with 28% of people below the federal poverty level compared with 12% in the US nationally. Hurricane Katrina shone a spotlight on these economic conditions as well as the environmental regulations that had been skirted. The EPA found that environmental legislation preventing discharges were not enforced, making what would have been a bad situation much worse.

Four years after Katrina, it was widely recognised that restoring wetlands and coastal forests was imperative to prevent worse storm damage in the future. A seismic shift in thinking had taken place in the academic community over the 40 years since the canalisation of the Mississippi, with scientists understanding more fully the significant role wetlands play for urban development in mitigating the impacts of hurricane storm surges.

The past practice of canalising rivers, which had been seen as expedient for economic growth had the opposite effect, undermining any hope for sustainable coastal development. In July 2009, the Army Corps of Engineers closed and blocked off the main navigation channel, the MRGO.

The once-admired shipping channel was widely blamed for the destruction caused by Katrina and, by 2010, the Corps had embarked on a “comprehensive” MRGO ecosystem restoration scheme.

The main goal was the “restoration and conservation of estuarine habitat areas”. This plan was made possible because of enabling legislation created after Katrina, the Water Resources Development Act of 2007.

The plan includes the construction of a freshwater diversion to restore historic salinity conditions in the ecosystem, which would help to re-establish historic habitat types, such as cypress swamp. Tens of thousands of square kilometres of wetlands were identified to serve as part of the line of defence against future hurricanes.

What lies ahead

The federal government asked an independent panel of experts in 2009 to review the Corps’ investigation of levee failures during Katrina and its plan to avoid such a catastrophe happening again.

Although there is consensus on the role of wetlands in helping to mitigate the impact of hurricanes, there continues to be discussion and differences in opinions as to what level of risk should be accepted. For example, should New Orleans be prepared to withstand a 100-year storm or a 500-year storm? The standards for this preparedness require more resources.

“For heavily-populated urban areas, where the failure of protective structures would be catastrophic, such as New Orleans, the [100-year] standard is inadequate,” the independent panel of experts concluded. Instead, the city should be protected by a “500-year or maybe 1,000-year protection”, the type of engineering standards used in earthquake zones or along major rivers, said Richard Luettich, from the Institute of Marine Sciences at the University of North Carolina and a member of the panel.

The US suffered an above-average summer for major hurricanes in 2011, and over the past 10 years the country has experienced seven out of 10 of the most deadly and costly hurricanes since records began. Last year, the US experienced three 500-year events, including Hurricane Irene, which hit New England and devastated much of Vermont.

Looking back to Katrina, the most deadly and costly of hurricanes to hit the US, the most enduring message would appear to be that extreme weather events are likely to happen sooner rather than later.

As a footnote, when Hurricane Isaac battered New Orleans in August this year, exactly seven years after Katrina, the rebuilt levees and defences largely withstood the onslaught.


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