Perhaps you noticed that it rained last night.

An "atmospheric river" plowed through the Portland area Dec. 17, dumping rain onto the city. In the past 24 hours, the National Weather Service measured 1.5 inches of rain in the West Hills and 3.1 inches on Mount Tabor.

But you know what you didn't see? Shit in the Willamette River.

Despite the deluge, Portland didn't experience a sewer overflow last night. That announcement was made today by the proud parents of the city's sewer system, the Bureau of Environmental Services.

Newcomers and curmudgeons may wonder: What's the big deal? Must we really celebrate that the river isn't filled with feces? But as recently as seven years ago, sewer overflows into the Willamette were common. As little as a tenth of an inch of rain could overwhelm Portland's sewer system and send wastewater spewing into the drink.

But under the management of City Commissioner Dan Saltzman, the city spent $1.4 billion on the "Big Pipe" project—huge tunnels on both sides of the river sending what you flush down the toilet to a waste treatment plant off North Columbia Boulevard. The Big Pipe eliminated 94 percent of sewer overflows.

(Its completion in 2011 is among the reasons why beaches and inflatable rafts in the Willamette are still a relative novelty.)

Commissioner Nick Fish, who now manages the Bureau of Environmental Services, is celebratory.

"One inch of rain. No overflow," he tells WW. "The Big Pipe is working and the Willamette is the big winner. Bring it on, mother nature!"