Lake Pontchartrain is central to the book’s account of New Orleans as a low-lying city dependent on pumps and canals: it was the intended outlet for drainage water, but during flooding it also became a source of water flowing back through the city’s drainage network. At Memorial Medical Center, the lake’s approach marked a decisive change in how staff understood the threat around them.

The Lake in New Orleans’s Drainage System

New Orleans occupied low ground below sea level, so runoff had to be collected and pumped into surrounding lakes. In the uptown drainage section, a single pumping station served 11,700 densely populated acres around Baptist. It lifted water into a relief canal, which carried it to another station for pumping high enough to flow into Lake Pontchartrain. Plans to expand the area’s pumping and canal capacity had not kept pace with development; buildings rose while the proposed work underground remained undone.

Floodwater Returns Through the Canals

During the crisis, flooding did not simply recede as water was pumped away. In some parts of New Orleans, levels rose again when Lake Pontchartrain overtopped levees and spilled into drainage canals running through the city. At Memorial Medical Center, water gushed from sewer vents and advanced along Claiborne Avenue. A doctor explained to ICU nurse Cathy Green that it was coming from the lake, not the Mississippi River; the water had already reached the avenue, which she estimated was about fifty city blocks from the lakefront.

The Lake’s Approach to Memorial

From the hospital, staff watched water advance with hurricane debris ahead of it. Green initially struggled to make sense of the report that water was coming from Lake Pontchartrain. She then compared the advancing flood to footage of a tsunami whose broken wave continued across the shore as a gathering torrent. The comparison gave shape to what the lake’s distance and the water’s continued movement meant: this was not a small, temporary rise. For Green, recognizing that the lake was entering the city became the moment when the situation at Memorial changed decisively.