Concerns over other Icicle dams

January 24, 2022

Concerns about dams in the Icicle are not limited to Eightmile Lake.

Engineers retained by the Icicle Peshastin Irrigation District have reached more optimistic conclusions than the Department of Ecology's Dam Safety Office on at least the dams at Colchuck and Square Lakes.

As reported here on November 20, 2020, the Dam Safety Office has rated all the Icicle dams -- Colchuck, Square, Klonaqua, and Eightmile Lakes -- as "high hazard." It did not claim they are in imminent danger, but all of them, in its view, need significant work and more inspections, and if any one of them failed it could cause substantial downstream damage. All four dams are operated by the irrigation district and are within the Alpine Lakes Wilderness.

Plans are underway to fix the Eightmile Lake dam. Ecology is proposing to pay or reimburse the irrigation district for at least part of the costs of rebuilding that dam. The big issues there, under the Wilderness Act and state water law, are whether the rebuilt dam can be larger or allow more water withdrawal than before.

Independent engineers from Pacific Engineering and Design of Seattle inspected the other three dams in September when water levels were low. Their draft reports seem to support the irrigation district's claim that at least the Colchuck and Square Lake dams do not justify the state's hazard rating.

Their report on Colchuck concludes: "The dam appears to be in generally good condition." It noted a small gap that could erode further on the outside of the dam wall, but claims it "does not threaten the structural integrity of the dam. Repair is not urgent and may be accomplished with other maintenance operations within the next five years." In other words, no big deal.

Engineers did not find the Square Lake dam in as good a shape because it is settling in places, some mortar has cracked, and its spillway needs repair. It noted the repairs already planned by the irrigation district and concluded that those repairs would restore the dam to better condition "than original". Sealing the mortar should be done sooner rather than later, per the report. The irrigation district agrees.

Klonaqua Lake is the only dam that has big problems, according to the engineers. The irrigation district has already acknowledged this. Because this dam is built atop old logs that are rotting, the irrigation district was already planning to replace it. The engineers agree this should be done "within five years".

Still, the engineers do not seem alarmed: "Although deteriorated log cribbing is suspected to be present throughout the embankment, complete and sudden collapse of the dam does not appear likely. . . . . Minor repairs to replace or reinforce the log cribbing is not practical. Complete replacement of the dam would be an appropriate course of action to address the dam's condition."

All three of these reports are only drafts, concluding with this disclaimer: "Due to the general and cursory nature of this report, these opinions and recommendations are presented in lieu of any warranties, expressed or implied. This report should not be interpreted as an exhaustive and comprehensive study due to the limited inspection and report timeframe."

Nonetheless, they represent the opinions of independent engineers after on-the-ground inspection of each dam. Moreover, the Dam Safety Office's conclusions themselves were based on what it acknowledged as "preliminary inspections."

The next steps will await the engineers' final reports. The question then will be how much the Dam Safety Office is willing to accept the conclusions in those reports. This could focus attention on the rationale for its hazard ratings. How much are they based on the structural integrity of the dams, versus the potential threat to downstream owners who were allowed to build in the flood plain?

The other half of this equation is the Alpine Lakes Wilderness itself. To reduce impacts on it, the irrigation district is already proposing to replace the Klonaqua Lake dam by helicopter. Depending on what Dam Safety officials might require at Square, and particularly Colchuck Lake, access for repairs could become a major issue.

Until these interrelated questions are resolved, the fate of these Icicle dams remains uncertain.