Kai Ryssdal: Memphis, Tenn., is bracing for the worst from the surging Mississippi River. The crest is expected to hit sometime tonight, and then roll on downstream toward New Orleans.

By the time all’s said and done, flood losses along the river may be the worst since Hurricane Katrina in 2005. All you have to do is look in the mirror if you want to know who’s picking up the tab. From Washington, Marketplace’s Scott Tong reports.

Scott Tong: Normally in Memphis, the Mississippi River spans half a mile wide. Now, it’s three miles.

Virgial Bailey volunteers at am emergency shelter at Cummings Street Baptist Church.

Virgial Bailey: There are some homes that are covered completely, rooftop and everything — covered. You can’t even tell there was a house there.

The worst flooding since the 1920s will cost billions, and many people have no flood insurance. For them, the federal government tends to swoop in and declare emergency disaster zones. Tennessee’s Emergency Management Agency is already asking for federal help, says spokesman Dean Flener.

Dean Flener: That declaration will provide assistance for uninsured homeowners who experienced damage who would qualify for that individual assistance. And that would help them repairs on their homes.

Not much help — grants top out at $30,000, typically what a mere six inches of water does in damage.

Flood insurance pays out a lot more, but only 5 percent of American choose to buy it. And there are problems there, too. Robert Hartwig at the Insurance Information Institute says premiums are vastly underpriced. They don’t send a signal that, hey, living by water is risky.

Robert Hartwig: The problem with respect to flooding is that that signal is not strong enough. The signal is deliberately muted by the flood insurance program, on the direction of Congress.

Artificially cheap insurance means premiums don’t bring in enough for the payouts. So the difference — you guessed it — comes from federal borrowing and a bigger national debtload.

In Washington, I’m Scott Tong for Marketplace.