Some high-hazard dams rated unsatisfactory — The Grand Junction Daily Sentinel

Harvey Gap Reservoir via the Applegate Group.

From The Grand Junction Daily Sentinel (Dennis Webb):

The YT Ranch reservoir is small, with a storage capacity of just 125 acre-feet (an acre-foot is about 326,000 gallons of water). Bill McCormick, the state’s dam safety chief for the Division of Water Resources, said there’s some question whether the dam even should be categorized as high-hazard and whether instead it should be listed as significant-hazard, meaning it only poses a threat of significant structural damage but not loss of life if it failed when fully filled…

Either way, the dam has been undergoing annual inspections and state dam safety officials hope to see its owner, now [Laramie Energy], eventually repair it. Meanwhile, the reservoir remains under a storage restriction, allowed to store only about half of its capacity, McCormick said…

Elsewhere in the Grand Mesa area, a restriction was lifted in November on storage in Big Battlement Lake after its owner, the city of Delta, did repair work to address seepage issues at the dam there. Big Battlement is upstream of Cedaredge.

Big Battlement is a high-hazard dam that previously had an unsatisfactory rating.

Following is a rundown on some other high-hazard dams in the region that currently are rated unsatisfactory:

  • Ward Lake on the Grand Mesa, upstream of Cedaredge. It’s an earth dam built in 1958, and is owned by the Surface Creek Ditch & Reservoir Co. Its normal storage capacity — what it can hold before water goes through the spillway, rather than how much more it can hold in flood conditions before the dam is overtopped — is 1,710 acre-feet. But it was purposely breached in preparation for replacement of the outlet works and can’t currently hold water, McCormick said. He said those construction plans are currently under review by the state and the work may take place this summer.
  • Grass Valley (Harvey Gap), north and upstream of Silt in Garfield County. This earth dam was built in 1892 and is owned by the Silt Water Conservancy District. Its normal storage capacity is 5,060 acre-feet. McCormick said that a few years ago the district fixed a problem with its outlet works, and dam officials eased a storage limit, but storage still is limited to no higher than a foot below the spillway until that deteriorated spillway can be addressed. He said his agency is working with the district on getting funding for that work.
  • Gurley, above Norwood, owned by the Farmers Water Development Co. It’s an earth dam built in 1961, and its reservoir’s normal storage capacity is 9,000 acre-feet. McCormick said the dam has a stability problem on its downstream slope involving a small slide last spring, and engineering work is being done regarding a repair.
  • Stillwater #1 in Garfield County, upstream of the community of Yampa. Owned by Bear River Reservoir Co., it is an earth dam and was built in 1939 with a normal storage capacity of 6,088 acre-feet. McCormick said it has seepage issues above a certain reservoir elevation and so it has a storage restriction. “I think they’ll be moving forward with some engineering on that here in the near future as well,” McCormick said.
  • Lawn Lake Flood

    From The Grand Junction Daily Sentinel (Dennis Webb):

    It’s been nearly four decades since a dam last had a major failure in Colorado, but the incident remains high on the minds of state dam safety officials.

    The Lawn Lake dam’s rupture in Rocky Mountain National Park in 1982 also caused the failure of a downstream dam, killed three people and caused extensive damage in the Estes Park area.

    “We use that as a training tool for our staff, our dam owners,” with a goal of keeping such an incident from ever happening again, said Bill McCormick, chief of dam safety for the state Division of Water Resources…

    At the start of the new year in Colorado, new dam-safety rules went into effect that are intended to account for the possibility of wetter storms in the years and decades to come due to warming temperatures.

    “We’re not sure when the storms will come but we know they will and we’re planning against those likely increases in the extreme events, just in the magnitude of the extreme events,” McCormick said.

    A focus of the new rules is better designs for spillways to help dams accommodate a higher volume of water during a storm.

    McCormick said the new rules resulted from a 2018 study on future extreme regional rainfall in Colorado and New Mexico. State and federal agencies were involved in the research…

    “One of the things that came out of that was a recommendation to accommodate increases in temperatures due to climate change into our rules and regulations,” he said.

    He said although the study was inconclusive as to whether there would be more or fewer storms in the future, it indicated a good likelihood of wetter storms because warmer air holds more water…

    McCormick said 432 high-hazard dams are in the state, but he said that descriptor is a common source of confusion. People tend to think a dam classified as high-hazard dam is in poor condition, and that’s often not the case.

    Dams get that classification based on the potential for downstream structures to be impacted with a water depth and velocity that could cause loss of life if the dam fails. McCormick said all it takes is for one structure to be deemed vulnerable under the evaluation criteria for the dam to get that classification. Colorado dams with a high-hazard rating are inspected once a year. Those in the significant hazard classification, meaning their failure wouldn’t likely cause loss of life but could cause major property damage, are inspected every other year. Low-hazard dams are inspected every six years.

    McCormick said different design standards also apply to the various classifications of dams.

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