Water flow through the Cascade flume was restored in November after a section of the structure north of Purgatory Resort collapsed over the summer.
A temporary pipe is now installed to bridge the collapsed section, allowing water to flow again at a reduced capacity, said Art Steimer, operations manager for Xcel Energy’s Tacoma Hydro Generating Station. Xcel Energy is the owner and operator of the channel.
“The flume is back in service, and it was a huge effort to get that done, but the biggest motivator was the community impact,” Steimer said.
The flume follows a path north of Purgatory and west of the Cascade turn on U.S. Highway 550. It is a critical water source for Purgatory Resort’s snowmaking operations and for downstream users, including Electra Sporting Club. Below Electra Lake, water carried by the flume is used to generate hydroelectric power at the Tacoma station.
The collapse occurred in May after water that escaped the damaged flume reportedly caused terrain erosion and caused even more of the flume’s support structure to collapse.
Some residents near Electra Lake have speculated that the flume may have been overfilled, contributing to the collapse, though Xcel Energy has not determined the cause of the failure.
“We do suspect that there could have been a blockage in the flume which would have caused the water to back up and spill over, which eroded the hillside and caused the collapse,” Steimer said. He emphasized that there was no historic flow event or unusual surge that contributed to the failure.
However, just days before the damage became obvious, the water flow through the 102-year-old wooden waterway surged to record levels, at least according to data collected at the U.S. Geological Survey monitoring site.
On May 15, USGS recorded the discharge at 71 cubic feet per second – nearly double the second-highest rate ever recorded, however Steimer said those metrics are often inaccurate.
The flume has the capacity to transport water at up to 400 cubic feet per second, and during spring run-off, the typical flow sits around 100 to 200 cubic feet per second, he explained.
Steimer estimated that permanent repairs will likely take two more years to complete.
The extended timeline is partly because of the flume’s historic significance, he added. According to the U.S Forest Service, the structure is eligible for inclusion on the National Register of Historic Places, which means any construction near or on the structure will require additional consultation and permitting with the Forest Service and the State Historic Preservation Office.
Additionally, the timeline is tied to the design process, the Federal Energy Regulatory Commission’s approval of the plans and the flume’s high-elevation location – roughly 9,000 feet – which limits the construction season to a narrow window, Steimer said.
jbowman@durangoherald.com
