Posted on 01 March 2012
Foiling flooding with wetlands protection
Foiling flooding with wetlands protection
New Orleans has begun a project to protect and restore wetlands in the Mississippi Delta in order to increase resilience against flooding, hurricanes, and rising sea levels caused by global warming. This is a reversal of previous tactics, which relied solely on dams and river levees. Research has shown that wetlands play a crucial role in the defence against flooding.
Keywords: flooding, wetlands, climate adaptation, resilience, biodiversity
Hurricane Katrina in 2005, when the dams of New Orleans burst, was the worst civil engineering disaster in US history and one of the country’s worst natural catastrophes. Eighty percent of New Orleans was flooded after the hurricane ripped through, 1,500 people died, and almost a million people were displaced. Some 16,000 offices and factories were flooded, and 40 schools were destroyed. The city’s recovery has been slow – the current population in the city proper is still almost half as large as it was before the disaster.
New Orleans is especially vulnerable to flooding. The city is located in a depression between the Mississippi River and Gulf of Mexico that is up to five meters deep. They city is also surrounded by water on three points of the compass. And it is threatened by flooding from hurricanes, its river, and heavy rainfall.
Hurricanes are common – the Gulf Coast has been exposed to one major hurricane each year since 1994, and 2005 alone saw 26 named storms and 14 hurricanes. This precarious situation is compounded by global warming, which is expected to bring with it a rise in sea levels and an increased probability of big hurricanes. In combination with subsidence (gradual land sinking) in the Mississippi delta, sea levels may rise by over one metre in New Orleans in the coming century.
Heavy wetland losses
On top of all this, the protective wetlands of the Mississippi Delta continue to be destroyed. These constitute 30% of the total coastal wetlands in the United States, but account for 90% of the country's wetland losses. This is primarily due to erosion along the coast, caused by dams along the river that prevent the deposition of sediments. Industrial activity and hurricanes have also contributed. Wetlands protect against flooding caused by hurricanes by slowing down storm waves. In the case of New Orleans they can reduce the waves by several metres before they reach the town.
The lesson learned from Katrina by politicians and researchers is that New Orleans cannot rely solely on its larger damming operations, locks, and pumping systems. The town has instead incorporated a strategy of several lines of resistance in order to fortify its defensive power: restored wetlands, improved damming, more logical planning in terms of land use, and improved emergency protection (see also Chengdu
). The plan is to swiftly restore as much wetland as possible through a combination of methods: restoration of the natural delta formation, construction of new wetlands with dredged material, and the construction of facilities for water control and new river levees.
New attention to protection
Wetlands have received increased attention as an effective method of solving multiple problems in urban environments, including the protection of biodiversity (see also Abbotsford
). In the case of New Orleans, a restoration of wetlands also means the protection of an ecosystem which is vital to the whole region. This was the primary aim of previous plans never implemented.
But after Katrina revealed the protective value of wetlands against flooding, restoration plans received new attention. In November 2005, the state of Louisiana appointed an agency for the protection and restoration of the coastline, where for the first time the restoration of wetlands is included as a task. And in the New Orleans masterplan for 2010, wetlands have a central role in the chapter covering green infrastructure and resilience. New Orleans will promote the protection and restoration of wetlands through land use planning, regulation, acquisitions of land, co-ordination within both public and private domains, financial aid and the establishment of new local regulations.
Uphill battle for financing
Despite the significance of wetlands for a much wider region than New Orleans itself, the city has been struggling to push these directives through. It still has a long uphill battle ahead in implementation and financing.
A. Kazmierczak, J. Carter, 2010, "New Orleans: Preserving the wetlands to increase climate change resilience", from Adaptation to climate change using green and blue infrastructure. A database of case studies. http://www.grabs-eu.org/membersArea/files/new_orleans.pdf
“Effects of Hurricane Katrina in New Orleans”, Wikipedia, http://en.wikipedia.org/wiki/Effects_of_Hurricane_Katrina_in_New_Orleans
The City of New Orleans, http://www.nola.gov/
Armando Carbonell, Douglas J. Meffert, 2009, Climate Change and the Resilience of New Orleans: The Adaptation of Deltaic Urban Form, Lincoln Institute of Land Policy Working Paper, https://www.lincolninst.edu/pubs/dl/1677_892_AC%20Replacement%20Final.pdf
Bev Betkowski / University of Alberta, 2009, ”Price point established for restoring wetlands”, University of Alberta Research Services Office, http://www.uofaweb.ualberta.ca/rso/news.cfm?story=91969
Key data are retrieved from the UN World Urbanization Prospects: The 2011 Revision, http://esa.un.org/unup/unup/index_panel2.html
Text by: Martin Jacobson