Adaptive Opportunism of Infrastructural Landscapes in the Mississippi Delta
Travis Bost (MDesS)
Project Overview
The Bonnet Carré Spillway is a large flood control structure in Southeast Louisiana along the Mississippi River that consists of a 1.7 mile long concrete weir and a 14 square mile floodway landscape. The project is part of a systemic flood control strategy of reservoirs, levees, and floodways for the entire Lower Mississippi. However, from the time of its construction its function has expanded from its simply initial technocratic, decadenal operation that acted on nature, to include numerous fluid exchanges between urban and natural ecologies including economic, recreational, industrial, and plant/animal environmental functions. For these reason the spillway is a valuable case study for future hybrid human-urban-mechanical-natural ecological landscapes.
Project Information
Located 13 river miles above the City of New Orleans, the Bonnet Carré Spillway, set up by the Mississippi River and Tributaries Project in 1928, is a flood control structure on the Lower Mississippi River and part of an extensive, distributed control strategy for the management of annual Spring and sudden flood events along the whole of the lower river. In addition to the dozens of upstream reservoirs on the river’s tributaries and the continuous line of constructed and reinforced natural levees, the Bonnet Carré is one of three floodways that all for an operable distributary from the river’s main channel to relieve the heightened pressure and gauge heights of the main river. However, of the three the Bonnet Carré has the most unique position in terms of its function and intimate implications for the formation of urbanization and the production of human-natural landscapes. Whereas other flood control mechanisms contribute generally to the safety of the system as a whole, this spillway is directly linked to the safety, formation, and cultural landscape of New Orleans and the surrounding delta urbanization.
The form of the river is an aggregated geography of a great many local human transformations throughout the system’s land use. Lying at the very end of a watershed that covers 41% of the continental United States’ territory makes the urban areas here particularly vulnerable to the coordinate weather patterns and land use decision up river. In the delta, the river’s channel is the highest point of topography in the area, leaving all urbanized areas literally in its shadow. The structure is operated approximately once every ten years depending on the scale of seasonal flooding. Once the river’s gauge at New Orleans reaches 17 feet, the Mississippi River Commission gives the order to open the bays of the spillway’s nearly two mile long weir to relieve flood height. This process is a highly calculated, slow, and laborious process. The spillway operation team from the New Orleans District of the US Army Corps of Engineers organizes for a certain number of the 350 bays of the weir to be opened progressively by means of two cranes lifting the weir’s 7,000 wooden timbers. At full capacity the structure may allow up to 250,000 cubic feet per second of river water to poor into the nearly fourteen square mile floodway and eventually into the saline Lake Pontchartrain, six miles to the northeast, and from there to Mississippi Sound. Within the spillway, the water is channeled by guide levees that continue perpendicular to the river’s mainline levees and cleared sections of the otherwise wooded landscape allow for the water’s swift flow while great pits and borrow channels allow for increased capacity of floodwater retention. The floodwaters pass through forest, swamp, and marshlands, and before reaching the brackish waters of the lake, they pass under rail and road bridges, over pipelines, around utility poles and conduits, and across numerous recreation areas of the hybrid landscape. At the end of the average one to two month opening event, the river’s threat to the city has been reduced, and with great deposits of sediment left over and the complete reworking of the spillway’s previous topography, the landscapes is completely transformed anew, imitating artificially the historical meandering flooding of the pre-human river.
While the spillway’s technocratic, designed operation replaced a natural-historical deltaic land-forming process with a machine-controlled operation, the function and form of the spillway as a landscape evolved dramatically to serve as a more innovative, fluid, and synthetic model of urban landscapes and infrastructure. As originally conceived in response to the Great Flood of 1927, the spillway and the greater strategy of the MR&T project represented a massive shift in strategy of flood control and therefore in generally conceptualizing the urban-nature dualism. A ‘levees-only’ policy that maximized flow rates of the river was traded for a strategy of outlets that mimicked artificially the historical condition of the delta. This had significant impacts for urban imaginary concerning the soft landscape of the territory. Accordingly, as spillway operations continued throughout the 20th century, the landscape began to take on those re-orientations in popular and formal conceptualization.
With each opening of the spillway, thousands of tons of sediments were left by the river in the fore apron and center channel of the spillway which must be removed in order for the project to function properly in the next event. This then becomes the basis for a new economy and human-natural ecology. The Army Corps of Engineers, after every operation, organizes a competitive bid process for contractors interested in excavating the deposited sands that are then used in construction projects and the regular raising of lawns and green spaces in the sinking soil of region. Clay sediments are also extracted for the sole use of the Army Corps for the construction and reinforcement of levee works. Meanwhile, the borrow pits created in these excavation works are then repurposed for human recreational and animal ecological functions. The pits are refashioned as hills, ramps, and mud basins for ATV users; they stocked with fish for recreational fishing; and they become breeding grounds for species once losing great amounts of territory such as alligator, egrets, and shellfish. In this way, again, pre-human ecologies are recreated to fit both the demands of natural and human existence, thereby encouraging a more fluid and interwoven urban-nature space.
Additionally, the spillway has a function as a spectacle of human-natural mediation that communicates the relationship being forged between humans and the environment in the process of urbanization. The structure itself, like many of the early Modernist engineering structures, is an architectural landmark of democratic, rationalizing aesthetics. Like dams and aqueducts of the era, the spillway is visited regularly by residents near and far to see the machine’s operation and production of nature. However, where once the project stood as a curious battle of human and machine over an unruly nature, the spillway’s operation is still a spectacle but one of a common, synthetic co-production process of urbanized nature, and a naturalized urbanism while still functioning as an infrastructure for both. The numerous supplementary functions accrued in the spillway over the course of its operation have increasingly been recognized by the Army Corps which has recently made efforts to formally recognize and spatialize them. With the issuance of a masterplan for the spillway in 2009, spaces were officially allocated for all various recreational and economic functions of the spillway, thereby expanding the role of the Army Corps to one of providing both technical protection from periodic dangers and daily social value while reconnecting urban areas with their surrounding environments as well as the means of their production. The spillway therefore stands as an exemplary case study for an expanded, more integrated understanding of urbanization, nature, and infrastructure for the future of city-making.