St. Charles Parish, LA
The Bonnet Carré Spillway and Flood Zones in St. Charles Parish
When the Mississippi River threatens to overwhelm New Orleans's levees, the Army Corps opens a set of gates in St. Charles Parish and lets the river flow into Lake Pontchartrain instead. That structure -- and the floodway land built around it -- carries real, specific consequences for land ownership here.
This page covers what's specific to St. Charles Parish. For the general explanation, see the national guide.
Why the spillway exists
The Bonnet Carré Spillway was completed by the US Army Corps of Engineers in the 1930s, following the catastrophic Great Mississippi Flood of 1927, as part of a broader national rethinking of how the river's flood risk should be managed. Rather than relying purely on ever-higher levees to contain the entire river's flow past New Orleans, the Corps built the spillway as a controlled relief valve: a series of gated bays along the river in St. Charles Parish that, when opened, divert a portion of the Mississippi's floodwater across a floodway and into Lake Pontchartrain, reducing the volume and pressure the river's levees downstream have to hold back through New Orleans.
The floodway itself: land designed to flood
Between the spillway's control structure and Lake Pontchartrain lies the floodway itself -- a corridor of land specifically designed to be inundated when the spillway operates. Much of this floodway is low-lying, forested batture and wetland, and land within it is generally subject to a federal flowage easement: even where the underlying land remains privately owned, the federal government holds the right to flood it when the spillway is opened, and permanent structures within the floodway are generally restricted or prohibited as a result. This is a genuinely distinctive land-ownership situation, different from an ordinary floodplain designation elsewhere -- it's not just elevated flood risk, it's land the government has an active, exercised right to intentionally flood.
A structure that gets used -- not a dormant piece of infrastructure
The Bonnet Carré Spillway has been opened periodically since its construction whenever Mississippi River flow reaches levels that threaten the safety margin of New Orleans's levee system, and it saw an unusually active stretch of openings during the 2010s compared to earlier decades. This page does not assert a complete, current list of opening dates or years, since that operating history continues to be updated -- but the durable takeaway is that this is a working, actively used piece of flood-control infrastructure, not a historical structure that has sat idle. Anyone evaluating land near the spillway or its floodway should treat the possibility of a future opening as a real, recurring operational fact of the area rather than a remote or purely historical risk.
What to check before buying land near the spillway
For any St. Charles Parish parcel near the Bonnet Carré Spillway, confirm directly with the US Army Corps of Engineers, New Orleans District, whether the specific parcel sits within the spillway's floodway footprint and, if so, what flowage easement or structure restrictions apply to it -- this is fundamentally different information from an ordinary FEMA flood-zone lookup and needs to be confirmed separately. For land outside the floodway itself but still in the general vicinity, pull a current FEMA flood-zone determination as you would for any Louisiana parcel, and ask St. Charles Parish's planning department whether any local building or elevation requirements apply given the area's flood-control history. A title examination should also specifically check for any recorded federal flowage easement affecting the parcel, since that's a distinct encumbrance from an ordinary levee-district or drainage servitude.
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Connect with a local land specialistSources
- Bonnet Carré Spillway — US Army Corps of Engineers, New Orleans District (accessed 2026-09)
- National Flood Hazard Layer / Flood Map Service Center — Federal Emergency Management Agency (FEMA) (accessed 2026-09)
- St. Charles Parish, Louisiana — 64 Parishes (Louisiana Endowment for the Humanities) (accessed 2026-09)
Last reviewed 2026-09