When one thinks about the protection and security of the nation’s civil infrastructure they may tend to think on fairly small scales. In this light, thinking on the scale of securing an entire city by developing protective devices over a time period of up to 100 years may be considered to be far-fetched. Plans of this nature for the protection of New Orleans are, however, currently undergoing serious evaluation. The core problem that needs to be addressed is summarized in a recent paper that I wrote recently:
“Due to a combination of a decrease in river sediment supply, channel confinement and disconnection from the floodplain, sea-level rise, and land sinking (subsidence), the Mississippi Deltaic Plain is disappearing at rates estimated on the order of 44 square kilometers (17 square miles) per year.”
Essentially the Gulf and, more importantly, the city of New Orleans is sinking. As time goes by, the city gets lower and its vulnerability to severe weather events increases. One proposed innovative solution requires a reversal in the thinking of the engineering control of river systems. Over many years the standard approach for flood control and protection on the Mississippi has been to build levees that confine the main channel. As seen in Hurricane Katrina, this approach is not always effective. Further, over the long term, a confinement approach compounds the problem. With the levees in place, the sediment in the river, which could be used to balance land loss by subsidence, is transported to the outer edges of the delta system and deposited in the deep water off the continental shelf.
The idea on the table is to reverse this trend and dismantle the established infrastructure by breaching the river levees downstream of New Orleans. This will result in a diversion of the currently confined sediment into shallower water leading to the creation of new landmass in the form of delta lobes. Modeling by Kim et al (2009) indicates (over a time period on the order of 100 years) that a significant amount of new land will be created in the Gulf by this process. This land will not only provide diverse natural habitat but also provide extremely effective storm surge buffers for the City.
The breaching of the levee system clearly upsets both the standard practice of infrastructure engineering and established political systems. The levee-breaching proposal also sits squarely at the center of the current paradigm shift toward developing secure and sustainable infrastructure.
Effective infrastructure protection needs to be considered across a wide range of space and time scales – not just weeks and acres, but multiple years and hundreds of square miles.
In looking toward building sustainable infrastructure, we should not fight nature but develop designs that directly utilize its rhythms and cycles.
Vaughan Voller is the Director of Graduate studies for the Master of Science in Infrastructure Systems Engineering at the Technological Leadership Institute and is Professor and Associate Head of the Department of Civil Engineering at the University of Minnesota. One of his current National Science Foundation support research projects is directed at developing computational models of the growth of sediment delta systems in the Gulf of Mexico.
[image credit: vlup2us65 via Flickr]