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A rain garden at Holloway and Jules avenues in the Oceanview-Merced-Ingleside, one of 151 citywide, is part of the city’s flood control system.

Rain garden on Valencia Street in San Francisco.

Rain garden on Valencia Street in San Francisco.

The last of the lovely autumn weather will soon slide away, and next up on the calendar is November, usually dank and drizzly in this part of the world. Daylight-saving time will end, and it will be as dark as a raven’s wing by late afternoon. The rains will come soon enough, and we’ll be glad to see them. Goodbye drought.

But San Francisco is not a rainy city. Street drains back up, and an occasional downpour produces flooding. Nothing serious, as they have in the Midwest or even along the Napa and Russian rivers, but trouble nonetheless.

I remember as a reporter a couple of seasons ago wading through the ground floor of a coffee house on Folsom Street in the Mission. The water was ankle-deep and foul-smelling. After two days of rain, Mission Creek, which had been lurking under the street out of sight for years, had resurfaced. I interviewed the business owner, who blamed the city for not preventing the flood with better drainage. He was madder than a wet hen. It made for good TV.

But now the city’s Public Utilities Commission has taken steps to better control runoff from rainstorms. We’ve had two or three mild winters, so the system hasn’t had a real test. But the rains are coming, and we’ll see.

One of the steps is a series of what officials call “bio-retention planters,” which are short depressions like trenches on the edges of streets and sidewalks designed to collect and absorb runoff from streets, sidewalks and parking lots, so the rainwater doesn’t overwhelm the sewer system. But nobody wants to celebrate drains and sewers, even if they are green. So now the city is calling them rain gardens.

There are 151 of these rain gardens all over the city from Ocean Beach to the bay. And they come with three things: a geography lesson, an urban challenge and a chance for ordinary citizens to help out the city.

First, the lesson. Most of the bigger rain gardens come with signs that explain San Francisco’s water landscape. Everyone knows the city is surrounded on three sides by salt water. But it is also divided into eight watersheds: three in the western part of the city where the rainwater flows into the Pacific Ocean; the rest where the water flows unto the bay. There are two active nearly natural streams: Lobos Creek in the Presidio and Islais Creek, which begins as a tiny stream in Glen Canyon Park at the feet of the grandly named Coyote Crags. It then ducks into pipes and tunnels to emerge near the Caltrain tracks.

Mission Creek runs under most of downtown and South of Market. The first structure built by Europeans began at the edge of a marshy lagoon where Spanish missionaries built a thatch and brush hut and named it after St. Francis. It meets the bay at a cove now named for Willie McCovey.

The other watersheds include one that runs into the bay at Yosemite Slough in the Bayview district and another, smaller watershed in Visitacion Valley.

My own encounter with the rain gardens began at where Valencia Street runs into Mission Street at the foot of Bernal Heights. This one represents both the urban challenge and a solution.

The rain garden here consists of a couple of small street gardens at Mission and Valencia and a block-long depression, like a shallow street trench 2 or 3 feet deep heading north on Valencia. Native plants and sedge grow in the trench as they have for years. But on one of the days I walked by, the garden was full of trash: bottles, papers the wind had deposited, urban junk.

It looked like a mess. But on the northern end, where Tiffany Avenue and Valencia meet, I met Kelly Teter, a planner for the city’s Public Utilities Commission. What I was looking at, she said, was part of the vast Islais Creek watershed where runoff from the hills and Noe Valley ran, all underground. And this, she said, was the Valencia and Mission Green Gateway.

I was skeptical, but Teter was upbeat. Help was on the way, she said. First came a Public Works cleanup crew, which arrived a day or so later and picked up seven or eight bags of trash, a reminder that this is an urban garden. But the remedy to the unkempt garden was in flyers she passed out inviting neighbors to adopt the Valencia Street garden and become an official city rain guardian.

The guardians, all volunteers, keep an eye on the local rain gardens, and keep them clean and take care of them between the regular quarterly city maintenance. It grew out of a rainy day program where residents “adopted” city storm drains and kept them clear until city crews could get there. It’s a big job: San Francisco has 25,000 storm drains and more than 1,000 miles of sewers. So far about half the city’s 151 rain gardens have been adopted by rain guardians.

More information is at www.rainguardians.org.

Kevin Parry, a native San Franciscan who is retired but spent a lot of time working on a ranch in Winnemucca, Nev., moved back to the city and became interested in helping out with the storm drain project. When the rain garden effort began, he signed up for that as well.

He lives on the Great Highway and decided to adopt a number of rain gardens that line Sunset Boulevard in the Parkside district. “About a mile of them,” he said. He’s interested in plants and water. “Water is life,” he said. “I want to help take care of the city.

“A huge perk of my volunteer work is the privilege of naming them,” Parry wrote me in an email. So he named the most beautiful of his gardens after his cousin Roger, a cowboy who died in an accident on a ranch in Nevada. “My cousin taught me everything I know about being a steward of the lands we inhabit,” Parry wrote.

He works in his cousin’s memory. “I want to make a difference,” he said.

Carl Nolte’s columns appear in The San Francisco Chronicle’s Sunday edition. Email: cnolte@sfchronicle.com

Carl Nolte is a fourth generation San Franciscan who has been with The Chronicle since 1961. He stepped back from daily journalism in 2019 after a long career as an editor and reporter including service as a war correspondent. He now writes a Sunday column, "Native Son." He won several awards, including a distinguished career award from the Society of Professional Journalists, a maritime heritage award from the San Francisco Maritime Park Association, and holds honorary degrees from the University of San Francisco and the California State University Maritime Academy.