As interbasin transfers go, the Potter Valley Penstock isn’t as impressive as the Adams Tunnel in Colorado. It’s a 3m diameter tunnel running 21km from Grand Lake to Mary’s lake, a drop of only 33m. But… it goes 1200m under the peak of the Continental Divide, diverting Colorado River water bound for the Gulf of California into the Front Range instead, eventually flowing into the Mississippi.
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The first is the closest proximity of named feeder creeks on the divide. Of course there are an infinite number of places where rain falling on one side or the other of a line ends up in very distant places, but the most obvious one is a ridge traversed by Willits Watershed Rd. between Willits and Redwood Valley.
On the left, Davis Creek feeds Outlet Creek which joins the Eel at the Covelo Rd. bridge between Longvale and Dos Rios. On the right, Rocky Creek flows to the Russian River.
@Cdespinosa this reminds me of the cool factoid about the Kootenay River in BC, which passes just under 2km from the headwaters of the Columbia River (Columbia Lake) before then following its own course for over 100km only to finally discharge into the Columbia.
The second is more fun: an outlet from Van Arsdale Reservoir on the Eel feeds a mile-long penstock under the Laughlin ridge to feed a hydroelectric generator in Potter Valley.
The discharge from this plant irrigates Potter Valley as the East Fork of the Russian River, whose source is actually the Eel River.
As the 120-year-old powerhouse hasn't run since 2021, PG&E plans to remove the dam and restore the Eel to free-flowing, managed by the Round Valley tribe for salmon restoration.
As interbasin transfers go, the Potter Valley Penstock isn’t as impressive as the Adams Tunnel in Colorado. It’s a 3m diameter tunnel running 21km from Grand Lake to Mary’s lake, a drop of only 33m. But… it goes 1200m under the peak of the Continental Divide, diverting Colorado River water bound for the Gulf of California into the Front Range instead, eventually flowing into the Mississippi.
@Cdespinosa Now I want to compare this to the Snowy Mountains Scheme, to understand where it fits in a global hierarchy. I’ve been meaning to visit the point at which it delivers water under the continental divide (“Great Dividing Range”), which is a 2-night 3-day affair.
@Cdespinosa there are giant water pipelines all over the place here. I use the Flatiron penstocks as a landmark to locate my house in satellite images. There’s another big one that crosses over US 34 east of Estes Park.
Not my water however, I have a private well.
I was in Estes this morning. One of these days I need someone to drive me through the canyon so I can actually enjoy the scenery. (It’s like 17 that way, and even more dangerous to speed through.)
Water has to be pumped from lower lakes up to Grand Lake to flow by gravity through the tunnel. Multiple hydro plants on its half-mile drop on the east slope generate plenty of power to raise the water on the west side. But how does the power get back to the pumps?
Through the water tunnel.
In a 69kV conduit on the roof of the tunnel, insulated with nitrogen gas.
That’s why the only thing you can see at either portal of the gravity-fed tunnels are serious electrical substations.
