At least 11 dams in Southwest Colorado are classified as high-hazard, which means their failure could cause at least one death downstream, including a dam near Durango that was leaking and is being rebuilt.
The aging Stagecoach Dam 25 miles north of Durango has been razed and will be replaced by a concrete dam and spillway the state hopes will improve safety. As a result of seepage at the dam, the Division of Water Resources required the level of water behind the dam be maintained 4 feet below full.
“We really weren’t worried about Stagecoach failing because we control the inflow,” said Alfred Hughes, superintendent of Xcel Energy’s hydroelectric plants at Tacoma Station just downstream from Stagecoach Dam and in Ophir and Salida.
Hughes said the dam outlived its useful life. He said the dam seepage was disturbing, but he said it was not the threat to human life posed by some of the nation’s other 84,000 regulated dams.
The average age of dams across the country is 52 years, with many needing prompt attention, said Keith Ferguson, an engineer with Denver-based HDR One Co. and incoming president of the Association of State Dam Safety Officials.
The American Association of Civil Engineers gives the nation’s dams a letter grade of D overall, Ferguson told the Durango Herald.
Dam failures have happened before in Colorado.
On Aug. 3, 1933, Castlewood Canyon Dam in Castlewood State Park failed, releasing water into Cherry Creek and flooding Denver 30 miles away. Two people were killed.
On July 15, 1982, Lawn Lake Dam in Rocky Mountain National Park failed and flooded downtown Estes Park. Three people lost their lives.
Federal dams such as those at Vallecito Reservoir and Lake Nighthorse are regulated from Washington, D.C. Other dams are under state regulation, which in Colorado is done by the Division of Water Resources. The Federal Energy Regulatory Commission becomes involved in dams connected to hydroelectric generation, including the two dams that hold back Electra Lake, Stagecoach and Terminal.
In Montezuma County, the dam at Totten Reservoir, built in 1965, is kept 5 feet below full because of a crack in the upper embankment.
Vallecito, Lemon, Ridges Basin, McPhee and Jackson Gulch, all high-hazard federal dams. Narraguinnep, Totten, Summit, Stagecoach, Terminal Dam at Electra Lake and Durango Terminal Dam are all high-hazard regulated by the state.
Navajo Dam, which is in New Mexico although much of the reservoir is in Colorado, is a high-hazard federal dam.
The Colorado Division of Water Resources said in a report that 14 dam-safety incidents were recorded involving seepage, embankment settlement and excessive upstream slope damage.
The state inspects high-hazard dams yearly. Dams that present significant hazard are inspected every other year and low-hazard dams every six years.
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