Denver Water distances itself from risk assessment of Ritschard Dam at Wolford Reservoir

A truck drives out to Ritschard Dam, which forms Wolford Reservoir, on July 13, 2016. The dam has settled two feet downward and moved eight inches horizontally since being built in 1995.
A truck drives out to Ritschard Dam, which forms Wolford Reservoir, on July 13, 2016. The dam has settled 2 feet downward and moved 8 inches horizontally since being built in 1995.

By Brent Gardner-Smith, Aspen Journalism

KREMMLING – Denver Water has taken steps to distance itself from a recent risk assessment of Ritschard Dam, which forms Wolford Reservoir five miles north of Kremmling.

The 21-year-old dam has found to be moving slightly and settling more than normal and a risk analysis workshop was held in February by a group of experts assembled by the Colorado River District, which owns the dam and reservoir.

After the risk workshop John Currier, the chief engineer for the River District, wrote a memo to the district’s board saying “a key conclusion” of a consultant review board is that “the dam is safe” and “there is no need for immediate action.”

Currier also wrote in his April 7 memo that the “key parties and participants” in the February risk workshop “included 1) the State Dam Safety Branch, 2) Denver Water, 3) our consultant review board, 4) our engineer, AECOM and 5) River District staff.”

But on May 2, Robert Mahoney, the director of engineering for Denver Water, sent Currier a letter critical of his April memo.

“In the memorandum, you characterize Denver Water as a ‘risk estimator’ and an active participant during the workshop,” Mahoney wrote. “Denver Water takes exception to these characterizations. At no time did Denver Water participate in the workshop as a risk estimator, nor was it ever invited to participate as a risk estimator on the panel.”

Mahoney also said that Denver Water “disagrees with characterizations in the memorandum implying that Denver Water was an active participant and that we concluded and agreed with the findings of the risk estimators. Denver Water’s role in attending the workshop was that of a concerned observer.”

Currier included the letter from Denver Water in a July 7 memo to the River District board. The memo and the letter were made public this week when the public agenda was released for the district’s July 20 board meeting in Glenwood Springs.

Mahoney raised other concerns in his letter as well.

“Based on our observations, the workshop and your memorandum only addressed the probability of a dam failure consequence,” Mahoney wrote. “While the probability of a dam failure appears low, dam failure is not the only potential adverse impact of concern to Denver Water. The probability of cracking in the core of the dam, which could reduce storage capacity, has a much greater range of uncertainty.”

Denver Water currently leases 40 percent of the water in Wolford Reservoir from the River District.

The reservoir can store 66,000 acre-feet of water and on July 14 the dam was holding back 65,240 acre-feet.

When its lease expires at the end of 2020, Denver Water is slated to become a part owner of the water in the reservoir.

“The River District will convey ownership, use and control of 40 percent of storage space and water right in Wolford Reservoir to Denver Water,” according to Jimmy Luthye, a communications specialist with Denver Water who checked Friday on the status of Denver Water’s stake in the facility.

As Jim Pokrandt, director of community affairs at the Colorado River District put it on Friday, “Denver Water currently holds a 40 percent lease. After 2019, it will be a 40 percent owner.”

The upstream side of Ritschard Dam, which forms Wolford Reservoir.
The upstream side of Ritschard Dam, which forms Wolford Reservoir.

Dam has issues

In his letter, Mahoney also suggested that developing a plan to fix the dam would be “beneficial.”

“According to Mr. Dick Davidson (of AECOM), cracking of the core has a 50 percent annual probability of occurrence starting in 20 years (the time criteria set for the workshop and probability estimation),” Mahoney wrote. “Given this uncertainty, it would be beneficial to develop plans now to remediate Ritschard Dam in the event of a crack.

“Further, based on the information presented at the workshop, Denver Water does not agree that Ritschard Dam is functioning as designed because no dam is designed to function with the degree of movement observed at Ritschard Dam to date.

“As addressed in the April 27, 2016 letter from Bill McCormick, chief of the Dam Safety Branch of the state engineer’s office, Ritschard Dam is in the category ‘of dams with significant issues’ and is on ‘an abnormal trend,'” Mahoney wrote.

Ritschard Dam is 122 feet tall,  1,910 feet wide, and sits across Muddy Creek, which flows into the Colorado River east of Gore Canyon. It was built for the River District in 1995 at a cost of $42 million by D.H. Blattner and Sons of Minnesota.

The dam has an impermeable clay core that is covered on both the upstream and downstream sides with rock fill, including shale rock excavated on site during construction.

In 2008, engineers working for the river district noticed the dam had settled downward by a foot-and-a-half, instead of the expected normal settling of one foot.

They decided to install monitoring equipment, including inclinometers, which measure slope angles.

Engineers for the river district have since installed an increasingly sophisticated array of monitoring devices. And they’ve verified that the dam has settled over 2 feet downward.

The dam has also moved horizontally, by 8 inches, at a location about 40 to 50 feet from the top of the dam.

Mike May, an engineer with AECOM, told the river district board in January 2015 that because of “poorly compacted rock fill,” the dam’s rocky outer shells are still moving, especially the downstream shell, and that the clay core of the dam, which is somewhat elastic, is also moving.

While the dam does not have “a global stability problem,” May said the concern is that if enough movement occurs, it could cause cracks in the clay core.

Water could then find its way into those cracks, start transporting material and widening the cracks, and the dam could eventually be at risk of failing.

Ritschard Dam, which creates Wolford Reservoir on Muddy Creek north of Kremmling, is moving slightly, but steadily. The Colorado River District expects rehabilitation of he dam to be expensive.
Ritschard Dam, which creates Wolford Reservoir on Muddy Creek north of Kremmling, is moving slightly but steadily. The Colorado River District expects rehabilitation of the dam to be expensive.

Abnormal behavior

McCormick, in his April 27 letter referenced by Mahoney, also included Denver Water as part of the risk assessment group.

“At the conclusion of the meeting it was the opinion of the participants, CRD, AECOM, risk analysis consultants John Smart and Larry Von Thun, Colorado Dam Safety and Denver Water that the risk of sudden failure of the dam by any of the failure modes analyzed was remote,” McCormick wrote. “It was also agreed that given that determination the need to continue to actively pursue physical modifications to the dam was not warranted at this time.”

McCormick also said that the results of the risk analysis session “now allow the Colorado River District and Colorado Dam Safety Branch to return to more normal reservoir operations with confidence that public safety is not being compromised.”

However, McCormick also noted that “due to the remaining uncertainty of the deformation behavior we agreed that Ritschard can only be classified as ‘conditionally satisfactory’ and that continuing action with respect to monitoring and observations is required by Colorado River District to operate the reservoir as planned.”

In his letter, McCormick cited a presentation at the risk workshop by Dr. Gavin Hunter, a professor at the University of New South Wales who has researched deformation behavior in 130 embankment dams.

Gavin compared the magnitude of the settlement observed at Ritschard dam with other dams in his data set.

“The displacement observed at Ritschard exceeds the majority of the dams studied, with only half the available data,” McCormick wrote. “Dr. Hunter describes this as ‘an abnormal trend.'”

McCormick also noted that Gavin’s research on the amount of settlement at Ritschard put it in the “region of dams with significant issues” category.

As such, McCormick said the River District should develop a plan for remediation work on the dam.

“We would encourage the Colorado River District to fully appreciate the abnormal and as yet not fully understood behavior of Ritschard dam and put an appropriate timeline on the ‘foreseeable future,’ McCormick wrote. “Based on the analyses done to date one could reasonably anticipate that remediation work will be necessary at some point in the future. We strongly encourage the Colorado River District to continue to plan for such remediation to avoid undue pressure on the operation of that facility as might be caused by a sudden change in the dam’s performance.”

McCormick said Friday that a workshop to develop an “action plan” has been set for the third week of August.

A detail of the rock outer shell on the downstream side of Ritschard Dam.
A detail of the rock outer shell on the downstream side of Ritschard Dam.

Long odds

In his April 4 memo, Currier of the River District had written that the district’s analysis indicated that risk of failure of the dam from deformation was 1 in 100 million, while the risk of the dam failing by a “probable maximum flood” causing overtopping – a standard measure of risk – was one in a million.

He also explained why monitoring the dam’s movement was a better approach than trying to stop the dam from moving.

“With the dam failure risk so low, even with twice the current deformation, the estimators concluded that there is really no compelling technical or health, safety and welfare reason to embark on a remediation plan,” Currier wrote. “In fact, from a ‘do no harm’ perspective continued monitoring is equally if not more preferable to active remediation.

“While remediation might put to rest some nagging uneasiness about on-going deformation and when it might end, there is no absolute certainty that it would or should allay that uneasiness.

“In essence, remediation might replace one known uncertainty with a new, unknown, uncertainty. All dam owners are faced with some level of future uncertainty, we just happen to be keenly aware of it by virtue of extensive monitoring and investigation,” Currier wrote.

And in his July 7 memo sent to the River District board, Currier said an additional inclinometer has recently been installed at the toe of the dam to track movement, and that he would be sending Mahoney of Denver Water “a short response clarifying a few matters and inviting Denver’s continued involvement and expertise in the deformation issues.”

Normal ops to resume at Wolford dam — #ColoradoRiver District #COriver

Click here to read the latest board meeting summary from the Colorado River Water Conservation District. Here’s an excerpt:

The Colorado River District has found that there is no compelling safety reason to proceed with remediation of Ritschard Dam at Wolford Mountain Reservoir in Grand County, now or in the foreseeable future.

This conclusion comes after exhaustve study of the settlement and a failure-risk assessment of the rock-fill, clay-core dam put into service in 1995. The River District’s consulting engineers and a separate Consultant Review Board it commissioned, together with the State of Colorado Dam Safety Branch, have concluded that the dam remains safe.

#ColoradoRiver: Risk of failure at Wolford dam ‘very remote’ — The Grand Junction Daily Sentinel #COriver

Wolford Mountain Reservoir
Wolford Mountain Reservoir

From The Grand Junction Daily Sentinel (Dennis Webb):

A review has led to the determination that there’s no need for the Colorado River District to make potentially expensive repairs to its Wolford Mountain Reservoir dam in the foreseeable future and it can resume full filling of the reservoir.

The review found that the risk of the Ritschard Dam in Grand County failing is extremely low despite the deformation problems it has been experiencing.

“We’re a public agency and we’re pretty gratified that we’re not looking at a 30-plus-million-dollar fix right now,” River District spokesman Jim Pokrandt said.

The rock-fill, clay-core dam was completed in 1995. It has settled near its center by about 2 feet, a foot more than expected of it as an earthen dam.

Its crest also has moved about 8 inches downstream.

The district already has spent about $1.5 million to install instruments to measure the dam’s movement.

It has considered possible repairs ranging from injecting concrete into the dam to shore it up to rebuilding it. The latter is something the district several years ago estimated could cost $30 million.

The district is taxpayer-funded and includes Mesa County. Any repairs might have come at least partly out of a separate enterprise fund the district derives from revenues such as water sales.

The district has called the dam problem the most important issue it faces. The reservoir is on Muddy Creek, and the town of Kremmling is just downstream, where the Muddy meets the Colorado River.

The reservoir can hold about 66,000 acre-feet of water.

The district began to rethink how it should deal with the dam movement after a three-person outside team of dam experts said no immediate action was required.

In February, it then held a workshop on the matter with participants including, among others, the outside team of experts, the state Dam Safety branch of the Colorado Division of Water Resources and Denver Water, which has a leasehold interest in the reservoir.

Participants concluded that the risk of the dam failing from the movement in a given year is one in 100 million, compared to the normally acceptable one-in-a-million risk of the dam failing from a flood overtopping the dam.

“Thus, the deformation-
related public risk is much lower than other, normally acceptable dam-related risks,” the river district’s chief engineer, John Currier, said in a memo to the district board.

He wrote that the workshop participants concluded the chance of a dam failure from the problem is “very remote,” and that from a risk perspective “there is no compelling reason to proceed with remediation of the dam now or in the foreseeable future.”

“The dam is functioning properly, and has a very high probability of continuing to function properly even if deformation continues at the historical rate for many more years,” he wrote.

The district has been voluntarily keeping the water 10 feet below full as a precaution.

But those involved in the review agreed “that normal reservoir operation along with continued reasonable monitoring is appropriate,” Currier wrote, and that keeping water lower, while slowing down the dam’s deformation, merely prolongs how long it will take for that deformation to be complete.

Wolford Mountain Dam: ” The Consultant Review Board has emphatically emphasized that time is on our side” — John Currier

Wolford Mountain Reservoir
Wolford Mountain Reservoir

From The Grand Junction Daily Sentinel (Dennis Webb):

The Colorado River District has been given some breathing room for dealing with a problem dam at its Wolford Mountain Reservoir five miles from Kremmling.

A three-person outside team of dam experts has advised the district that the Ritschard Dam is safe despite the settling that has occurred there, no immediate action is required, and the district should be deliberate in determining how to address the problem.

“The Consultant Review Board has emphatically emphasized that time is on our side,” the district’s chief engineer, John Currier, said in a memo to the district board in advance of its meeting next week.

The recommendation comes as good news to the district, which has identified the dam as the most important issue it currently faces. It already has spent about $1.5 million to install sophisticated instruments to measure the dam’s settlement. Since its completion in 1995, the rock-fill, clay-core dam has settled near its center by about two feet. While earthen dams settle, in this case the drop was a foot more than expected. The dam crest also has shifted about eight inches downstream.

The three-person team, district staff and consulting engineers are now proposing that the district hold a workshop with the Dam Safety branch of the Colorado Division of Water Resources and Denver Water, which has a leasehold interest in the reservoir, to consider next steps.

“We were thinking that some kind of work would begin in 2016 or (20)17, to begin some kind of remediation program, but now we’re saying OK, let’s dig deeper into the issue based on this third-party finding,” district spokesman Jim Pokrandt said.

He said the finding means the district has more time to make sure it takes the right next steps regarding the dam. The most expensive repair would involve rebuilding the dam, which several years ago the taxpayer-funded district estimated could cost $30 million. Another approach could involve injecting concrete into the dam to reinforce it.

The original dam and reservoir project cost $42 million, including land acquisition, permitting, construction and other expenses…

The dam sits on Muddy Creek, a tributary of the Colorado River. The river district has consulted with the town council of Kremmling, which is downstream of the reservoir on the Colorado River, and Grand County commissioners. It also has held public meetings and kept emergency managers informed of the situation.

Bill McCormick, the state’s chief of dam safety, agrees that there is no reason for immediate concern regarding the dam.

“It is displaying some unusual behavior but (the findings of) all the analysis that’s been done to date is that it’s not creating unsafe conditions,” he said.

Still, he said he thinks everyone involved agrees there’s a long-term issue pertaining to continued settling, which requires a long-term solution.

“The long-term solution isn’t clear or obvious just yet but we’re continuing to work on it,” McCormick said.

Fixing ‘moving’ dam near Kremmling could cost $15M — Aspen Journalism #ColoradoRiver #COriver

Upstream side of Ritschard Dam, which forms Wolford Reservoir
Upstream side of Ritschard Dam, which forms Wolford Reservoir

From Aspen Journalism (Brent Gardner-Smith):

It could cost $15 million to dig up and recompact the rocks on the downstream side of the dam that creates Wolford Reservoir, north of Kremmling, in order to stop the dam from moving slightly, but steadily.

“It is a pretty significant surgery of the dam,” John Currier, chief engineer at the Colorado River District, told the district board July 22 during a presentation.

Ritschard Dam was built for the river district in 1995 by D.H. Blattner and Sons of Minnesota for $42 million. The dam is 122 feet tall and 1,910 feet wide.

The $15 million estimate to rehabilitate the dam includes a 35 percent contingency factor and is still preliminary, Currier stressed.

The project would include removing the top 25 feet of the dam and then stepping down the downstream face of the dam in layers to get to three “bad acting” zones of poorly compacted rock, some of which are 90 feet inside the dam.

“At some point that movement will compromise the ability of the core of the dam to hold back the water,” Currier said.

Currier said there are “no near-term safety concerns” regarding the dam’s current ability to hold back 66,000 acre-feet of water from Muddy Creek, which flows into the upper Colorado River east of Gore Canyon.

“We’re not in any crisis,” Currier said. “We’re just ready to move this forward.”

Engineers with the district noticed in 2008 that the dam had settled vertically by a foot-and-half instead of just 1 foot, as expected.

The dam has now settled 2 feet, at the rate of about an inch a year. And it has also moved horizontally, by about 8 inches, at a spot 40 to 50 feet below the crest of the dam.

The dam’s impermeable clay core is held in place by rock shells on both the upstream and downstream sides of the dam.

A detail of the rock outer shell on the downstream side of Ritschard Dam
A detail of the rock outer shell on the downstream side of Ritschard Dam

Trouble at some point

The upstream rock shell appears to have settled appropriately in place, perhaps because of varying degrees of water pressure on its face as reservoir levels have fluctuated.

But the downstream shell is still moving.

“At some point that movement will compromise the ability of the core of the dam to hold back the water,” Currier said.

Currier said construction-sequence photos indicate the movement appears to be related to how fill material above and below haul roads was compacted during construction.

The plan is to dig into sections of the shell, remove the poorly compacted rock, and then recompact those zones, mainly using the same rocks.

“The bad-acting layers may be more a function of how the material was placed, not the material itself,” Currier said.

Currier said a consulting engineer at the firm of AECOM had observed that the construction work is essentially “just a big dirt job,” albeit one that will require complicated sequencing and careful on-site supervision by experienced engineers.

Over the last six years staff and consulting engineers have taken a variety of steps to investigate the situation at Ritschard Dam.

A graphic of the issues at Ritschard Dam from the Colorado River District
A graphic of the issues at Ritschard Dam from the Colorado River District

$1.5 million spent

They’ve installed inclinometers, established an expert review panel, developed modeling and conducted lab tests on the core material to establish that the dam did not present an immediate safety problem.

The river district has now spent close to $1.5 million on instrumentation and analysis, Currier said, and recent work on a range of alternatives has given engineers enough information to move from the “what” stage to the “how” stage.

“We have a very good understanding of what solutions might, or might not work, and thus we can we have a great deal more confidence in our solution,” Currier said. “We’re confident that structural rehab is required.”

Currier said that simply storing less water in order to take pressure off the dam won’t solve the long-term problem.

In a memo to the board, Currier wrote “operating at reduced levels slows the deformation rate but does not stop the deformation.”

The river district has been operating the reservoir at 10 feet below normal levels since 2014 as a standard precautionary measure.

Another option looked at was installing a series of concrete columns down through the downstream shell of the dam in order to stiffen it, but Currier said it was ruled out due to higher costs and doubts about its effectiveness.

There is also the opportunity to increase the amount of water the reservoir can hold by increasing the height of the existing spillway, but Currier advised it was better to first just fix the dam to avoid a “permitting quagmire” by trying to also expand the reservoir’s capacity.

Water in the dam would likely have to be lowered or completely drained during the project in order to take enough pressure off the dam. Those lower water levels could cause ripples in regional water-supply operations, especially in a dry year.

But Dan Birch, the district’s assistant general manager, said water-supply concerns would not be the tail that wags the dog of the rehabilitation project and related safety concerns.

However, it was also noted that the project would take 220 days over two construction seasons and would likely have an affect on four years of water operations in all.

“It could have some impact on water operations for one year pre- and one year post-construction,” Currier said.

Currier and other engineers plan on continuing their analysis of the proposed solution, including meeting with the state dam safety engineer in August and continuing to ask a panel of experts to peer review the plans.

A refined proposal will be presented to the River District board in September as part of the district’s annual budget meetings.

Editor’s note: Aspen Journalism is collaborating with the Glenwood Springs Post Independent and The Aspen Times on coverage of rivers and water. The Post Independent published this story on July 27, 2015.

Ritschard Dam repairs are a top priority for Colorado River District officials #ColoradoRiver

Wolford Mountain Reservoir
Wolford Mountain Reservoir

From CBS Denver:

The Ritschard Dam on Wolford Mountain Reservoir near the town of Kremmling has some residents in the area concerned.

There have already been a few public meetings regarding the dam in Grand County. The Ritschard Dam has a clay core and is filled in around that with rocks, but the dam hasn’t held its shape. Something has happened with the settling of all the material over the past two decades.

“In 2009 it was discovered that pieces of the dam have settled faster than was expected by designers,” Jim Pokrandt with the Colorado River District said.

Sophisticated monitors have been placed inside the dam. The crest of the dam has settled down 2 feet, twice as much as expected — and also shifted downstream 8 inches.

“We’ve been studying that since 2009, spent $1.5 million or more on this, and we really can’t say why exactly, other than there could be some compaction issues that date back to construction time,” Pokrandt said.

Engineers have said it’s the river district’s top priority, and not fixing the dam could send a devastating flood down the Colorado River.

“Public safety is not at risk and it won’t be at risk because we’re going to take this quick action,” Pokrandt said.

Exactly how the dam will be secured and fixed won’t be decided until later in the year. One idea is making the dam and reservoir bigger.

“You can imagine that if you’re going to fix a settlement issue you might be scraping off part of the dam and rebuilding it. How much, we don’t know.”

Forty percent of the water in the dam is owned by Denver Water. The rest is to ensure water in the river for endangered fish and water for municipalities on the Western Slope. But making the reservoir hold more water brings in a whole new set of issues.

“It’s premature to talk about what the exact repair scenario could be,” Pokrandt said. “There’s no quick fix.”

The Colorado River District board will likely make a decision on how the dam will be fixed by the end of the year.

More infrastructure coverage here.

The Colorado River District, et al., are closely monitoring the settling of Ritschard Dam (Wolford Mountain) #ColoradoRiver

Ritschard Dam and Wolford Mountain Reservoir
Ritschard Dam and Wolford Mountain Reservoir

From the Sky-Hi Daily News (Lance Maggart):

Ritschard Dam impounds Wolford Mountain Reservoir, located on Muddy Creek just north of Kremmling. Construction on the Dam was completed in 1995 and falls under the auspices of the dam’s owners the Colorado River Water Conservation District.

Ritschard Dam is an earth-filled dam. As [Jim] Pokrandt explained, “With anything involving earth, settlement is expected.”

Unfortunately, as Pokrandt went on to explain, a portion of the dam has settled faster than the dam designers expected.

“The variations are small, but there is an abundance of caution,” he said…

“We are monitoring the conditions at the dam. The dam is not considered unsafe,” said Bill McCormick, chief of the Dam Safety Branch of the Division of Water Resources.

McCormick explained, “approximately four to five years ago there were anomalous instrumentation readings showing the dam had settled unexpectedly in ways that were not predicted in the design.”

“We have not identified a safety concern that has required us to put a restriction on the reservoir,” he pointed out.

According to Pokrandt, construction equipment visible on the dam is part of ongoing work to install measuring devices to gauge both water levels and movements within the dam.

Data collection and analysis regarding settlement of the earth-fill structure has been under way for several years now and the process will continue.

Pokrandt explained that any construction on the dam undertaken by the District, “will be very expensive” and the District wanted more information and data before any decisions were made regarding new construction.

More infrastructure coverage here.