Flood thy neighbor: Who stays dry and who decides?

levee in, they did a great job. It sucks for the folks down below, because, I mean, this is going to happen every year.”

When rivers flood now in the United States, the first towns to get hit are the unprotected ones right by the river. The last to go, if they flood at all, are the privileged few behind strong levees. While levees mostly are associated with large, low-lying cities such as New Orleans, a majority of the nation’s Corps-managed levees protect much smaller communities, rural farm towns and suburbs such as Valley Park.

But why Valley Park? It wasn’t the biggest city or largest employer along the Meramec. Its neighboring towns all had homes and industry in harm’s way, too. But after almost a century of planning to protect all these communities, the federal government built a single 3-mile levee, shielding the low-lying area of just one town.

Exploring why that happened offers a window into the nation’s flawed approach to controlling rivers, in which — an investigation by ProPublica and Reveal from The Center for Investigative Reporting found — life-and-death decisions are dictated less by sound science than by economics, politics and luck.

Levees have been the nation’s most common method of flood control for much of U.S. history, despite a major drawback: Levees protect the land immediately behind them, but can make flooding worse for people nearby by cutting off a river’s ability to spread over the floodplain — the flat, low-lying land beside the river channel. This is a basic matter of physics and something the Corps has known since at least 1852, when a report it commissioned demonstrated that as levees confine a river to a narrower channel, they force water to flow higher and faster. A levee such as the one at Valley Park, on just one side of the Meramec, creates a traffic-jam effect that forces water higher on the opposite bank and upstream.

Twenty-five years ago, before it built the Valley Park levee, the Corps predicted that saving the city would cause just a few extra inches of flooding in areas close by. But it reached that conclusion based on outdated models, without factoring in