Big Johnson Reservoir outlet works repair update

Big Johnson Reservoir via Dan Aquino
Big Johnson Reservoir via Dan Aquino

From The Colorado Springs Gazette (Matt Steiner):

The diminishing water level in the 280-acre lake south of the Colorado Springs Airport is intentional. Gary Steen, manager of the Fountain Mutual Irrigation Company that owns the Big Johnson, said Tuesday morning that his company has been draining the reservoir since the summer of 2016 and preparing to repair three outlet gates…

The irrigation company typically fills the reservoir in the fall and winter months before the irrigation season begins in early April. Steen said crews have been building a bypass pipeline for the last few weeks and will finish the work prior to April 1.

When Fountain Mutual built the reservoir in 1910, it took control of a water storage decree that dates back to 1903, Steen said. That decree allows the company to store up to 10,000-acre feet of water in the lake. But, according to Steen, sediment in the reservoir has diminished its capacity over the years to about 5,000-acre feet.

How safe are Denver Water’s dams? – News on TAP

Dam safety team conducts annual inspections, manages upgrades and trains for emergencies to keep facilities secure.

Source: How safe are Denver Water’s dams? – News on TAP

#OrovilleDam: What caused the catastrophic spillway failure?

Oroville Dam spillway collapse. Photo credit Californian Department of Water Resources.
Oroville Dam spillway collapse. Photo credit Californian Department of Water Resources.

From The San Jose Mercury-News (Paul Rogers and Matthias Gafni):

How did a giant, gaping hole tear through the massive Oroville Dam’s main concrete spillway last week, setting in motion the chain of events that could have led to one of America’s deadliest dam failures?

Dam experts around the country are focusing on a leading suspect: Tiny bubbles.

The prospect is simple, yet terrifying and has been the culprit in a number of near disasters at dams across the globe since engineers discovered it about 50 years ago. In a process called “cavitation,” water flowing fast and in large volumes can rumble over small cracks, bumps or other imperfections in concrete dam spillways as they release water during wet years. The billions of gallons of water bumping off the surface at 50 miles an hour create enormous turbulence that can form tiny water vapor bubbles that collapse with powerful force, and like jackhammers, chisel apart concrete.

“It starts with small holes, but it can break off big chunks of concrete,” said Paul Tullis, a professor emeritus of civil engineering at Utah State University and cavitation expert. “It’s like a big grinder. It causes concrete to be torn apart.”

It’s still too early to investigate the cavity on the spillway while dam operators at the nation’s tallest dam desperately drain billions of gallons of water down the damaged chute ahead of coming storms.

Cavitation at the Glen Canyon Dam via Flow Science.
Cavitation at the Glen Canyon Dam via Flow Science.

But the same phenomenon nearly caused the collapse of one of America’s other largest dams, Glen Canyon, a 710-foot tall behemoth on the Colorado River, in 1983…

When engineers entered the Glen Canyon Dam’s damaged spillway, they found a crater 32 feet deep and 180 feet long, and tons of concrete, reinforced metal and rock that had simply washed away. The right spillway had similar, but less severe damage.

They didn’t simply reconstruct the spillways, they introduced new technology with aeration slots — essentially ramps at vulnerable spots in the spillway to create an air pocket where water vapor could be disrupted and weakened. The physics gambit worked. In 1984, the runoff was equally as challenging, but Glen Canyon’s spillways had no problems.

Those fixes led the federal agency to retrofit two other large dams — Hoover and Blue Mesa — with aerators.

“It was a defining moment in dam design,” Bureau of Reclamation hydraulic engineer Philip Burgi told a magazine years later. “The world was watching how we were going to solve this problem.”

Similar fixes were added to the Tarbela Dam in Pakistan and Infiernillo Dam in Mexico, and now are common in new dams.

It could be months before the cause of the collapse of Oroville Dam’s spillway is known. The Federal Energy Regulatory Commission this week ordered the state Department of Water Resources to convene a panel of five dam engineering experts to oversee an investigation.

But despite the lessons from Glen Canyon, the Oroville Dam spillway apparently did not have aerators. The massive chute is 178 feet wide, as wide as 15 lanes of freeway, and just 15 inches thick in the middle. Sources at the Department of Water Resources say it hadn’t been retrofitted with aerators — likely one or two ramps, in the case of Oroville’s chute-style spillway, perhaps a foot high each, that would allow the water to flow over and reduce the risk of cavitation.

“Compared to the cost to repair that, it would be just a few million dollars,” said Tullis. “It’s not just a matter of money, it’s a matter of safety. It should have been a priority.”

When the main spillway failed, officials had to slow water releases. The lake, swollen from heavy storms, rose nearly 50 feet in five days and overtopped its emergency spillway for the first time ever, forcing the emergency evacuation of nearly 200,000 residents along the Feather River. The hillside below the emergency spillway eroded badly, leading to fears it would collapse, and send a wall of water into towns below. In recent days, dam operators have increased flows down the broken main spillway, dropping the lake level, and hoping it doesn’t further tear apart.

By Friday morning, state officials had lowered the water level at the 10-mile-long reservoir by 40 feet, especially important as three new storm systems were coming in.

“The threat level is lower. It’s much, much, much lower than what it was on Sunday,” said Bill Croyle, acting director of the State Department of Water Resources.

One concern that is certain to be a focus in the investigation are cracks in the main spillway in recent years. Records from the state Division of Safety of Dams show the cracks were seen in 2009. Also, crack repairs were done last in 2013, according to Kevin Dossey, a senior civil engineer with the Department of Water Resources.

“We made repairs and everything checked out,” Dossey said last Friday at a news conference. “It looked like it would hold, and be able to pass water.”

If the concrete patches came off, or the cracks worsened, however, that could have eroded the spillway, or it could have created enough of an uneven surface to start the domino-effect of cavitaton, experts said.

“It doesn’t take a whole lot of an imperfection when water velocities are very, very high,” said James Kells, a professor of civil and geological engineering at the University of Saskatchewan.

“When I first saw photos, the first thing that came to my mind was cavitation, just because of where the damage was,” Kells said. But he also began to think uneven concrete slabs or internal erosion below the concrete could be “viable causes.”

[…]

Another theory is that the drought dried the ground under the spillway enough that it shrank, creating a void of a few inches that cracked the spillway when huge volumes of water roared down this winter…

1967: Heavy snow melt in the Bighorn River basin raises the Yellowtail Dam reservoir to record levels, opening the spillway for 20 straight days. The Montana dam spillways suffers a hole the size of a semi-truck and trailer.

1977: The Karun Dam in Iran has more than 7,500 feet of concrete torn up on its concrete spillways.

1979: The Kebon Dam along the Euphrates River in Turkey suffers damage to two spillways; one had been running for 15 days, another just three.

1983: The Glen Canyon Dam takes on heavy snowmelt and rains leading to water coming perilously close to the top of the dam. Its two tunnel spillways open for the first time ever and both receive significant damage. Engineers create new aerator devices to fix the problem, a big turning point in spillway engineering.

1983: Hoover Dam, the nation’s most well-known, used its spillways in 1941 for initial testing and again in 1983 due to unanticipated high water levels, and both times a concrete elbow transition suffered cavitation damage.

Mid-1980s: Flaming Gorge Dam on the Green River in northeastern Utah and Blue Mesa Dam in Colorado suffer damage are both fixed with aeration devices.

#Colorado Springs responds to @EPA/CDPHE lawsuit

From The Pueblo Chieftain (Robert Boczkiewicz):

The city’s denial is its first response in court to a lawsuit that claims discharges of pollutants into Fountain Creek and other tributaries violate the laws. The discharges are from Colorado Springs’ stormwater system…

Colorado Springs asserted in Monday’s filing that it “has at all times been in compliance” with permits issued by the state agency to govern the discharges and the stormwater system.

The city contends it should not be subjected to court orders or monetary penalties that the environmental agencies want a judge to impose.

Colorado Springs also contends that allegations in the lawsuit misrepresent the facts of issues in dispute.

Colorado Springs with the Front Range in background. Photo credit Wikipedia.
Colorado Springs with the Front Range in background. Photo credit Wikipedia.

Rio Grande Reservoir outlet works project update

Rio Grande Reservoir
Rio Grande Reservoir

From The Pueblo Chieftain (Matt Hildner):

The reservoir’s outlet experiences what Smith calls a “hydraulic jump” because of a design flaw that allows air to surge along the ceiling of the tunnel. “It’s kind of a coke bottle affect,” said Smith, who also represents the Rio Grande basin on the conservation board. That flaw has limited the amount of water that can be released from the reservoir during periods of high inflows to 1,200 cubic feet per second. Smith hopes the repairs will boost that figure to between 1,800 CFS and 2,000 CFS. State lawmakers initially approved other repairs to the reservoir as part of the $30 million Rio Grande Cooperative Project in 2012. The current proposal would add another $10 million to that initial approval, although lawmakers would decide how much of that amount is grant or a loan…

Smith sees that cooperation between privately-owned irrigation reservoirs and other interests on the river as a model for advancing water projects.

The reservoir’s main purpose is to deliver irrigation water to just 62,000 acres of farm ground in the north end of the San Luis Valley. With a capacity of 54,000 acre-feet, it is one of only three reservoirs with significant capacity upstream from where diversions begin to pull from the river for agriculture. That means it plays an important role in replacing depletions on lower reaches of the river caused by groundwater pumping on the valley floor.

Pueblo West contracts for 6,000 acre-feet of storage in Lake Pueblo

Pueblo West
Pueblo West

From The Pueblo West View (Kristen M. White):

Pueblo West will have the right to store water in Pueblo Reservoir in the future, should the storage be needed, after the Metropolitan District agreed to enter into a subcontract with the Southeastern Colorado Water Conservancy District…

The master plan contract is between the Bureau of Reclamation and the water district, and Pueblo West now has a subcontract with water district for its storage rights.

The contract allows Pueblo West to begin paying for 10 acre feet, at the starting rate of $40.04 per acre foot of water, in 2017. But the contract gives Pueblo West the ability to store as much as 6,000 acre feet of water in the future should the storage ability be necessary.