Bonnet Carré Spillway

Bonnet Carré Spillway
Name	Bonnet Carré Spillway
Location	St. Charles Parish, Louisiana, United States
Coordinates	30°03′N 90°40′W
Opened	1931
Owner	U.S. Army Corps of Engineers
Type	flood control spillway
Waterway	Mississippi River to Lake Pontchartrain

Bonnet Carré Spillway The Bonnet Carré Spillway is a federally operated flood-control structure on the Mississippi River in St. Charles Parish, Louisiana, designed to divert excess river flow into Lake Pontchartrain to protect New Orleans and the surrounding Greater New Orleans metropolitan area. Constructed during the early 20th century as part of a system of levees, channels, and reservoirs, it is managed by the U.S. Army Corps of Engineers and has been used repeatedly during major flood events, influencing navigation, industry, fisheries, wetlands, and municipal planning in the Lower Mississippi Valley.

History

Conceived after catastrophic floods that affected the Lower Mississippi Valley and cities such as New Orleans and Memphis, Tennessee, planners from the U.S. Army Corps of Engineers incorporated the project into broader reforms following the Great Mississippi Flood of 1927, the Flood Control Act of 1928, and studies led by engineers connected with the Mississippi River Commission. Construction began under federal funding during the late 1920s and early 1930s alongside other New Deal-era and interwar public works initiatives influenced by policy debates in Washington, D.C. and legislative oversight from the United States Congress. Early operations intersected with commercial navigation interests represented by organizations such as the American Waterways Operators and riverine commerce stakeholders from Baton Rouge to the Port of New Orleans.

Design and Structure

The spillway's layout integrates a diversion channel, concrete control structures, wooden and steel bays, and floodplain terraces between the Mississippi River and Lake Pontchartrain. Its engineered elements reflect practices promoted by the Mississippi River Commission and standards used by the U.S. Army Corps of Engineers in projects like the Old River Control Structure and the Bonnet Carré Floodway-adjacent levee networks. The structural components account for navigation clearance for barge traffic tied to the Port of South Louisiana and include movable bay systems, a control building, and access roads connecting to Interstate 10 and regional routes near Kenner, Louisiana. Geotechnical design considered soils common to St. Bernard Parish and the Mississippi River Delta, while hydraulic modeling incorporated data from agencies including the National Weather Service and the United States Geological Survey.

Operation and Management

Operational authority rests with the U.S. Army Corps of Engineers, New Orleans District, which coordinates openings with the Mississippi River Commission and consults stakeholders such as the Port of New Orleans, Louisiana Department of Transportation and Development, and municipal governments of New Orleans and surrounding parishes. Decisions to open are based on river stages measured at gauges maintained by the United States Geological Survey and forecasts from the National Weather Service and the National Oceanic and Atmospheric Administration. Coordination involves communications with terminal operators, energy producers including Entergy Corporation facilities, industrial entities along the Mississippi River, and navigation authorities such as the U.S. Coast Guard to mitigate impacts on shipping and public safety.

Environmental and Ecological Impacts

Diverting freshwater and sediment into Lake Pontchartrain and adjacent wetlands affects salinity regimes, subtidal habitats, and fisheries resources important to communities in Plaquemines Parish and Jefferson Parish. Environmental assessments involve the U.S. Fish and Wildlife Service, Louisiana Department of Wildlife and Fisheries, and academic partners from institutions like Louisiana State University and University of New Orleans. Ecological consequences include shifts in oyster populations tied to conditions near the Chalmette National Wildlife Refuge and altered nutrient loads influencing algal dynamics similar to events monitored by the Environmental Protection Agency. Restoration and mitigation programs have drawn support from federal initiatives linked to the Coastal Wetlands Planning, Protection and Restoration Act and collaborative projects with non-governmental organizations such as the Lake Pontchartrain Basin Foundation.

Flood Events and Notable Openings

Major openings have occurred in response to high water from upriver events, notably the post-1927 planning era, the floods of 1973 and 1993 that affected the Upper Mississippi River corridor, and the widespread high-flow emergencies of the 2011 Mississippi River floods and the historic 2019-2020 high-water period. Each opening required interagency coordination among the U.S. Army Corps of Engineers, the National Weather Service, and state emergency agencies in Baton Rouge and New Orleans. These events impacted shipping schedules at the Port of South Louisiana and prompted emergency measures involving the Federal Emergency Management Agency and local parish authorities.

Cultural, Economic, and Community Effects

The spillway's operation influences commercial navigation tied to the Petroleum industry and commodity routes serving grain exporters and petrochemical plants near Garyville and Plaquemine. Recreational fishing and tourism in the Lake Pontchartrain Basin are affected, with ripple effects for businesses in communities such as Kenner and Mandeville. Cultural memory of major floods informs municipal resilience planning in New Orleans and shapes policy dialogues in the Louisiana State Legislature and among advocacy groups including conservation-oriented organizations and trade associations representing the Maritime industry.

Category:Mississippi River Category:Buildings and structures in St. Charles Parish, Louisiana