From The Denver Post (David Olinger):
Colorado is undertaking the largest emergency dam inspection program in state history, seeking to check 200 dams in 10 days, mostly along the South Platte River and its tributaries. All of Colorado’s high-hazard dams, which likely would kill people if they fail, withstood the recent record rainfall. But nine low-risk dams have breached, and an uncounted number of small ponds overflowed, contributing to the flood. Twenty other dams can be reached only by helicopter because roads below them washed out.
At least 55 engineers have offered to help the state dam safety branch with the inspections, and the agency has called all of its engineers in western Colorado to Denver.
In two days, “we had to write up the plan for what we wanted these engineers to do,” dam safety chief Bill McCormick said. “They’ll help do a workload that would have taken us six months.”
The inspectors will be looking for problems like increased seepage from large earthen dams, damaged spillways and clogged drainage outlets. Some small lakes and reservoirs might have to be drained for repairs.
McCormick, his deputy Scott Cuthbertson and John Batka, a safety engineer for dams along the St. Vrain and Big Thompson river systems, set out Thursday afternoon to see some of the known damage to the dams.
In Boulder County, at Pella Ponds Park, a trail system winds past a trio of ponds and lakes beloved by anglers and birdwatchers. The flood breached two, and their waters are pouring out. The parking lot is a cavernous hole, tipping over an outhouse at the edge. The trail, now a bumpy mix of gravel, stones, driftwood and landscape fabric, ends abruptly at a 10-foot-high cliff. The nearby St. Vrain River demolished this park.
“Utter devastation throughout the floodplain,” Batka said. “Whatever was in its path.”
Upstream, the river jumped its banks and formed new channels. The deluge filled McCall Lake, a high-hazard reservoir saved by its spillway.
At Left Hand Valley Reservoir, two spillways sent water over the edge. One, a staircase of concrete, survived with little apparent damage. The other, which doubled as the road to the reservoir, was destroyed. A 3-foot emergency berm now blocks the base of the access road. Above it, floodwaters carved giant gullies all the way to bedrock. It is among 70 reservoirs whose waters roared down spillways, some for the first time since they were built.
“This is a generational event,” Cuthbertson said, surveying the wreckage.
The dam safety program already took emergency action at 14 locations. One was Gaynor Lake, a Boulder County open space reservoir near houses and roads. When the lake filled, emergency workers brought in a backhoe to clear out clogged outlet ditches, leaving behind a mess of equipment tracks and a urine-like stench emanating from piles of dead cattails. Its embankment is temporarily braced with sand and gravel. McCormick watched the lake draining away for dam repairs. “We saw this as a serious condition,” he said.
He said Colorado residents can be thankful that its most hazardous dams met strict engineering standards and that grants from the Federal Emergency Management Agency’s national dam safety program helped train engineers and dam owners for this crisis. He said he hopes that a massive dam inspection program will find any hidden dangers — and reassure the worried people who call his office daily to report potential dam failures.
One came from a personal acquaintance who lives near the Button Rock reservoir in Larimer County. “Everyone in this neighborhood is on edge,” she told him.
From CBS Denver:
Record flooding continues in western and central Nebraska as the water that inundated Colorado flows east, but it appeared to cause few major problems because communities were able to prepare.
The National Weather Service says the South Platte River rose to 14.2 feet in North Platte to set a new record on Sunday. The previous record level of 14 feet was set in June 1935. The river also set a record in Brady at 9.85 feet Sunday — eclipsing the previous mark of 9.6 feet. Records were already set upstream in Roscoe, Neb., and Julesburg, Colo., late last week.
“I knew a dam had breached above Lyons, so the cops and I thought there was a wall of water headed our way. I remember being kind of freaked out.” [Gary Lindstrom] said he was relieved when the roadblock was moved east on 66 to 53rd Street.
Here’s a photo gallery from The Atlantic (Alan Taylor).