The dams holding back drinking water in the Southeast Alaska community of Wrangell are over a century old. They’re leaky, and some of the least stable dams in the state, according to the state Department of Natural Resources. A 2015 survey found the dams to be the second-worst in Alaska.
But to fix the problem, the borough needs to actually understand the problem. That’s proved to be its own issue, said Public Works Director Tom Wetor.
“Long story short, our dams were originally constructed in 1905, and we have some information and some drawings on the construction of those dams. However, they’re — I would say — somewhat incomplete,” Wetor said. “There’s contradictory information in one drawing versus another. One drawing says there’s metal sheet piling in [the dam]. Another one says that there’s not.”
“So,” he continued, “To be quite frank, no one knows entirely what the construction of the dams is made up of. So before we’re able to do any kind of modifications, or even understand what the modifications would need to be to improve on our dam stability, we need to understand what we’re working with.”
In late September, a team of engineers and borough staff worked to sample the dam soil and try to reach bedrock. Wetor said the team sampled multiple points, and was mostly successful in gathering the data they needed. A few times, they hit rocks, had equipment break, or paused because of concerns about the immediate stability of the dam.
He said there were a few tense moments when borough officials and engineers were considering activating a dam emergency plan, which could have involved trying to evacuate residents who live below the reservoirs.
Wetor said he’s “not a dam expert,” no pun intended, and can’t speak to all the possible implications of what happened during the stability analysis, so he’s eagerly awaiting the official engineering report.
He said the results of the report — expected within the next couple of weeks — will help the borough determine next steps.
“Best case scenario, the dam is more stable than what we thought it was going to be, and we can just add more material and increase the size of our dam and our stability that way,” Wetor said. “Worst case scenario, the dam is actually worse than what we thought it was, and there’s no safe way to raise or reinforce the current dams as they are, which could require entirely new dams being built down below the existing dams, and then demolition or deconstruction of the existing dams to bring things online.”
Moving forward, Wetor said the borough’s top priority is finishing a project to link Wrangell’s drinking water plant to the upper reservoir. Right now, the plant only connects to the lower reservoir.
The upper reservoir bypass is an important project for a number of reasons, including the potential for the borough to do serious work on the reservoirs.
“In order for us to be able to work on the dams, we’ve got to be able to essentially take one of them offline and perform some of this work,” Wetor said. “So having a bypass in line will give us a lot more flexibility and ability to do that.”
That bypass project already has just over $2 million in federal funds secured by Alaska’s congressional delegation. And a draft of borough infrastructure priorities for the coming year has the dam bypass at the top of the list.
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