Melba Martinelli, like many living in the lush forests along the Russian River, awoke Monday to surging water outside her mobile home.

The weekend storm that soaked most of California had passed, but the river that winds through Sonoma County’s wine country was still swelling, locked into its routine of steadily rising with mountain runoff — and was beginning to spill its banks in the Guerneville area west of Santa Rosa.

By the afternoon, roughly 500 homes, including Martinelli’s, were estimated to be taking in water as the river crested above 35 feet, 3 feet past flood stage.

“It stopped raining, but the water level just continued to climb,” said Martinelli, 55. “It was actually pretty scary. I didn’t know how I was going to get out of there.”

As it turned out, a fast-thinking neighbor on her street in downtown Guerneville flipped the camper shell of his truck, turning it into a makeshift raft, and paddled the two out.

“It worked really well,” Martinelli said as she stepped to safety on high ground a block away. “I didn’t even get wet.”

As high as the water got Monday, it could go higher. According to government forecasters, the Russian River is expected to drop below flood level in Guerneville early Tuesday before surging again Wednesday amid continuing rains.

The second crest, expected Wednesday evening, may be even higher, approaching 36 feet.

Still, though the flood stranded cars, submerged street signs and turned vineyards into small lakes, the fallout was familiar. The communities nestled along the Russian River — an area known for its small-town charm, quirky vacation resorts and award-winning Pinot Noir — has been here many times before.

The flooding surpassed that of December 2014, when heavy rains bloated the drought-parched river, but fell well short of disasters of past decades. The last big gusher struck on New Year’s Day 2006.

What the Russian River is doing this week, said people who study the waterway, is just what the Russian River does. In fact, the torrents raged on Monday only about half as furiously as they have raged in the past.

“This is the Russian River,” said Andy Watson, field office chief for the U.S. Geological Survey, who is in charge of measuring river flow. “What you’re seeing is pretty common.”

On Monday, the Russian was traveling through Guerneville at a rate of 43,000 cubic feet of water per second. The river drains a “substantial” area of 1,338 square miles, Watson said, and large flows are a matter of course.

“We’re in the same ballpark” as the 2014 flood, Watson said. “This is the topography around the Russian River. There are low-lying areas that flood. It’s almost kind of normal.

“It’s not the Mississippi,” he said, “but it’s a big river.”

Beginning Sunday, hundreds along the river took refuge with friends or family, or at a homeless shelter in Guerneville that extended its hours. Tuesday was supposed to be the first day for Guerneville schools to reopen after the holidays, but they will remain closed, officials said.

One person south of town, marooned at a flooded house, had to be rescued by a boat crew with the Russian River Fire Protection District, but no flood-related injuries were reported.

“It seems like we’re weathering it pretty good,” said Chris Helgren, emergency manager for Sonoma County. “But it’s hard to say until the floodwaters go away. And we’re still concerned about (Tuesday’s) upcoming storm.”

While several roads were closed Monday, and many homes and businesses were without power, many people were happy that the river hadn’t reached the 38 feet that forecasters had projected.

“I think we’re going to be OK,” said Bart Deamer, a San Francisco resident who had driven to his vacation home on Redwood Drive, finding his backyard deck and garden submerged, but not his home.

Last week, Deamer removed rugs and valuables from the first floor of the house in preparation for rain, and on Monday, he needed only to hoist a few remaining beds onto cinder blocks.

“It’s an extra 4 inches, maybe 6,” he said. “It gives you a good psychological feeling. That’s the main benefit.”

Victor Menjivar wasn’t as lucky. He woke early Monday to find floodwaters surrounding his apartment complex in downtown Guerneville. Fortunately, his brother had a canoe.

“That’s how I left,” he said, standing next to a small lake that had pooled between him and his home.

In nearby Forestville, the Mirabel Park mobile home community was awash in the river Monday morning, with 20 or so residents forced to flee. All that could be seen from an adjacent road was muddy water and the roof of the restrooms.

“I was hoping that the worst of the storm was going to go down south, but it hit us head-on,” said Bruce Harper, who took his trailer to the safety of high ground in a nearby park.

He and his wife didn’t expect they would be able to return until at least Thursday.

As the Russian River area has grown more affluent, homeowners and resort operators have plunked more money into flood control. More and more homes are on stilts. There are stairs and walls where none had been before.

Whether people should build, rebuild and rebuild again along the Russian River in low-lying places like Guerneville and Monte Rio is beyond the purview of the U.S. Geological Survey, Watson said.

“People always want to live close to the water. They hope they don’t get flooded,” he said. “That’s what they hope. I don’t know. I wouldn’t want to do it.”

Kurtis Alexander and Steve Rubenstein are San Francisco Chronicle staff writers. Email: kalexander@sfchronicle.com, srubenstein@sfchronicle.com Twitter: @kurtisalexander, @steverubesf