Record-shattering rainstorms across Colorado’s Front Range led to flooding that blew out at least six dams Thursday, stranding a Larimer County family on the second floor of their home and breaching a federal stormwater holding pond northeast of Denver.

The floods also overflowed a dozen dams in Boulder County, but no structural failures had been reported Thursday evening, according to Boulder city spokeswoman Sarah Huntley.

Water flows in Boulder Creek reached 4,500 cubic feet per second, more than twice the previous peak flow in 26 years of measurement, according to the U.S. Geological Survey Colorado Water Science Center. Normal flow is 100 to 300 cfs.

Bill McCormick, who heads the state Division of Water Resources’ dam-safety branch, said late Thursday that Colorado’s highest-hazard dams, whose failures would probably drown people, performed well.

“(But) we have a few weak spots we’re tracking,” he said. Among them is Baseline Reservoir, a high-hazard dam in Boulder County. He expressed confidence that the dam will survive record-setting days of rain.

Many less-hazardous dams were designed to withstand a 100-year rainfall, however, “And the rainfall we’ve had is exceeding the design of those dams,” McCormick said.

He urged people to be alert for damage to the hundreds, possibly thousands, of small earthen dams dotting the Colorado landscape, many of them too small to qualify for state safety inspections.

In Larimer County, five small dams in the Big Elk Meadows area failed, trapping a family up a washed-out county road, said John Schulz, a spokesman for the Larimer County Sheriff’s Office.

When a county emergency services worker hiked in to check on the family Thursday, he saw a wall of water smash through the home’s front door and flood the first floor. The family of three and their dog huddled on the second floor and waited to be rescued. The worker left a communications radio with the family to maintain contact.

As of Thursday afternoon, efforts to rescue the family had stalled. County Road 47, off the highway between Lyons and Estes Park, is washed out, preventing vehicles from reaching them.

Surging stormwaters channeling out of northeast Denver neighborhoods caused the rupture of the Havana Ponds dam inside Rocky Mountain Arsenal National Wildlife Refuge, located just northeast of Denver. The dam broke around 10 a.m. as overflowing water ripped out several concrete slabs.

The currents carved an 8-foot-deep gully through the refuge and washed across roadways. Refuge managers raced to a series of other stormwater holding ponds and opened valves to relieve pressure.

By evening, the Irondale neighborhood at the northwest edge of the refuge was evacuated because the massive amounts of water retained on the refuge could no longer be contained by an earthen embankment distant from the Havana Ponds.

“The system is well-designed. It’s just that this particular event is more than anything it’s designed for,” refuge manager Dave Lucas said at the scene.

State dam-safety inspectors fanned out Thursday to check conditions on larger dams where failures could be deadly.

Dam-safety engineer Ryan Schoolmeesters worked his way north from Denver, checking dams along Boulder Creek, Clear Creek and Bear Creek.

So far, “the dams seem to be in good condition,” he said in Arvada. “A few of the spillways have activated, which is what they’re designed for.”

As a result, “residents could see some high spillway flow” downstream, he said, causing “road flooding, water in yards.”

In Colorado, which has dammed nearly all of its rivers, hundreds of dams have become structurally deficient and in need of repairs.

According to a Division of Water Resources report for the year ending in October 2010, 359 dams are classified as high-hazard, meaning that their failure would probably kill people.

The state has dealt with deficiencies in these and other dams by limiting the amount of water they’re permitted to hold.

“There are a total of 176 dams restricted from full storage,” the state report read, “due to inadequate spillways and various structural deficiencies such as significant leakage, cracking and sliding of embankments.”

The state has made some progress since. As of October, 157 dams “remained on the dam-safety restricted-storage list,” the division’s latest report says.

Those are just the larger dams. Earthen dams less than 10 feet high or capable of holding less than 100 acre-feet of water are classified as nonjurisdictional and not inspected, Schoolmeesters said.

Four of the five Big Elk Meadows dams were classed as too small to inspect. All five failed.