LONGMONT — Longmont’s city manager declared a state of emergency Thursday morning as the rapidly rising St. Vrain River and Left Hand Creek effectively cut the city in two.

The rising waters, declared a “500-year flood” by city officials, forced neighborhoods to evacuate and major streets to close, including major north-south routes such as Main Street, Hover Street, Sunset Street and Airport Road. Police and city crews spanned the south side of Longmont to warn residents and redirect traffic, reporting the conditions they found to the city’s emergency command center, which city officials activated at 2:30 a.m. Later in the day, as the waters continued to rise, neighborhoods just east of Airport Road near Twin Peaks Golf Course were evacuated.

The blocked and flooded streets drove some to frustration as they tried to find a way across the swollen rivers. At Hover Street and Rogers Road, some residents tried walking north on the water-covered Hover despite police warnings. The St. Vrain crested Hover at Rogers Grove shortly before 11 a.m. Elsewhere, drivers went from roadblock to roadblock or else stacked up in massive traffic jams along Rogers, Hover or Ken Pratt Boulevard.

After Hover and Main were closed, the only way to get from the south end of Longmont to the north end was to take Ken Pratt Boulevard east until it connected with Third Avenue, and then go north and west on Third back into the city. And even that way proved difficult to reach.

“How does someone get out of here?” one driver shouted as he approached the Boston Avenue bridge from River Road — another roadblock. “You can’t go that way, you can’t go that way — this town is a maze!”

By 5:30 p.m., Police Cmdr. Jeff Satur said he didn’t anticipate re-opening any of the closed river crossings Thursday night.

City Manager Harold Dominguez’s emergency declaration ordered that residents evacuate “certain areas of Longmont experiencing or expected to experience flooding” as determined by his office. By the day’s end, the city would evacuate a dozen neighborhoods totaling 7,000 homes, along with commercial areas such as the Harvest Junction shopping center.

“The best thing right now is really for folks to stay home,” Dominguez said late Thursday afternoon, as he and emergency manager Dan Eamon took a short break from supervising the city’s EOC.

“In two minutes …”

Conditions often changed rapidly Thursday. During the noon hour, Don Potter stopped his truck near Boston Avenue and Price Road so he could take pictures of the flood. The waters rose abruptly, leaving him on the railroad tracks and his truck marooned.

“In two minutes, it completely cut me off,” Potter said.

“Now it’s washed all the dirt from underneath the tracks,” he said, pointing to areas where gravel and dirt were gone with the tide, leaving just the metal rails and wooden beams. “Which is kind of helpful, since it’s able to go through now. Just amazing.”

Potter’s son tried to pull the vehicle out with a chain but got his own truck swamped in the process.

“I’d say we can wait it out, but who knows?” Potter said.

The city did not agree. As onlookers watched from the tracks, a worker pulled through the water, driving a piece of heavy equipment.

“Hey, folks!” he yelled. “There’s supposedly a 10-foot wall of water coming this way! You need to GO HOME!”

Around the same time, Simon DeHerrera was pulling his trailer out of his driveway on his 3-acre, Flipside Organic Farm, on the west side of Airport Road just north of Ninth Avenue.

“Everything that I can lift — my tools, everything that keeps this little place going,” DeHerrera said.

Ten-year-old Eli Stratton-DeHerrera said he and his dad had been talking earlier with Eli’s great-grandmother, who lives adjacent to the farm. She said the last time she had seen water like this on the farm had been in the late 1940s.

Above water — for now

The first warnings came at 3 a.m. to residents of the St. Vrain flood plain, asking them to evacuate immediately. Some homes sat high enough to sit tight, with a front-row seat to what was happening.

“(The water) started crossing Hygiene Road and started filling up all the ponds over here and that’s when it started getting close to my grandma’s house. A 2-foot wall of water,” said Cody Trevithick, a Hygiene volunteer firefighter who lives in Longmont but was at his grandmother’s home that morning.

The St. Vrain runs south of Hygiene Road near her house, before the river crosses a bridge and rolls past the ponds at Pella Crossing. Trevithick said Thursday morning that he thought the home sat high enough that it would be OK — but not so for a shed and a 500-gallon fuel tank on the property.

“I was driving out; my uncle was backing out and the shed almost T-bones him,” he said. “I said, ‘Whoa, that’s something you don’t see every day.'”

Rose and Paul Swenby, who live just south of Hygiene on the east side of 75th, found “a river running down the driveway” at about 9 a.m.

“We got reverse-911 calls all night long,” Rose Swenby said. “They said this area, but I was just thinking they meant the canyons.”

“We’re above water — as long as it doesn’t go up another foot,” Paul Swenby said Thursday morning.

The mighty Missouri

In the Southmoor Park area, a new “Missouri river” was born — namely, Missouri Avenue, now full and flowing with water from nearby Left Hand Creek.

“It’s almost a catch basin,” said Norma Figgs, a resident of South Bross Street.

The waters came quickly. One neighbor, Heidi Platt, said she had been coming home from a job at 7:30 a.m. and could still drive across Missouri then. Just two hours later, police were advising residents to start checking their escape routes.

“If you live in here, you might want to consider finding a place to stay,” an officer shouted to watching neighbors on South Bross. “This is going to get worse.”

Another officer on South Bowen was more succinct: “You need to leave, now!”

The creek could be seen out of its banks on both the north and south side of a closed Pike Road. On the south, a curious crowd watched spillover fill the playground; north of the road, the waters successfully passed a newly-installed bridge but overflowed further downstream into Missouri, near Brookfield Drive.

“This is incredible,” said Melody Williams, as the chocolate-brown waves pounded just under the bridge and down the creek. “We’ve never had an ocean next to our home before.”

Another South Bross resident, Shara Sherwood, couldn’t help remembering the recent work done to shrink the Left Hand flood plain.

“I’m glad they got this flood project done, but I’m not feeling too good about it right now,” she said, laughing.

Her adult daughter, Samantha, replied: “Imagine if they hadn’t.”

Later in the afternoon, at the EOC, Eamon said the water’s rapid rise had been one of the challenges facing emergency workers.

“We’re getting feet rises in 15 minutes,” he said.

Closing up

As the waters rose up, a lot of places shut down, including the city’s parks maintenance facility on South Sunset Street. From the cul-de-sac Donovan Place, just north of the railroad tracks and within view of the city building, what was normally a barren, open field populated only by prairie dogs became a raging torrent of water.

The St. Vrain school district offices on South Pratt Parkway were also evacuated because of the high water. Classes, needless to say, were canceled for the day, and they’re canceled again Friday.

“I’ve never had a rain day before,” Longmont High School paraeducator Katie Klarkowski said as she watched the waters near her home in south Longmont. “Plenty of snow days, but this is a first.”

The north campground of St. Vrain State Park was evacuated as a precautionary measure, with campers moved to the south campground. By evening everyone was evacuated and the park was closed.

As of press time, the water had not taken out the Main Street Bridge, despite rumors that it was buckling.

“The information I have says that the Main Street Bridge is fine,” city spokesman Rigo Leal said. “Of course, in this particular crisis, things can change quickly.”

By 4 p.m., the rainfall had made this Longmont’s second wettest September on record, according to Times-Call weather expert Dave Larison. As of then, the city had 4.23 inches of rain for the month, with 3.91 inches of it coming from Thursday’s storm.

Police said the evacuated neighborhoods included, as of Thursday night: Harvest Junction business park, Southmoor Park, Creekside, Longmont Estate Greens, Champion Greens, The Valley, Golden Ponds, Willow Creek, Schlagel, Grandview Meadows, a trailer park near Boston and South Sherman Street, and the neighborhood at Main and Pratt.

Dominguez, Eamon and public works and natural resources director Dale Rademacher took a helicopter flight over the length of the city and over to Lyons. It was that flight, Dominguez said, that led them to evacuate neighborhoods that they previously had not known were in danger.

Anyone needing assistance with evacuation is asked to call the EOC at 303-651-8595.

Evacuation centers are at the St. Vrain Memorial Building in Roosevelt Park and at Niwot High School.

Scott Rochat can be reached at 303-684-5220 or srochat@times-call.com. Tony Kindelspire can be reached at 303-684-5291 or tkindelspire@times-call.com