Little snow, many birds on Salmon Creek trail

Posted: Sunday, May 31, 2009

An otherwise peaceful, jovial lunch on the helicopter platform near Salmon Dam was interrupted by a surprise attack of snowballs derived from a nearby late-melting snowbank. The perpetrator immediately received a well-deserved dump of snow down the back of the neck. There followed a brief battle, which was halted when a nice hard fast-ball zoomed straight for my head. I dodged. The hurler was removed from the pitcher's mound and relegated to far left field, where a good arm can be put to better use than throwing bean-balls. Peace was then restored with the offering of yummy German chocolate cake for a hiker's birthday.

From the platform, we had a clear view of the surrounding peaks whose snow cover was less than we expected. The reservoir behind the dam was almost empty - showing lots of mud, some dead tree trunks, a tiny trickle of water and a few pools of standing water. Although it is normal for the water level to be low in spring, AEL&P told me that the drawdown, for power, during the past two winters had been somewhat more than usual, because of the avalanches that cut our power supply from Snettisham. The water level is now rising again.

On the way up the trail, we found little snow. The stairs were as steep as ever - maybe slightly steeper than last year - and still required long legs, or a scramble for those of us not possessed of long legs, to accomplish some of the rises. We spotted several mountain goats on Blackerby Ridge, including a nanny and kid. Another goat on a cliff a bit below the dam eyed us suspiciously and slowly withdrew into dense timber higher up.

Some of the hikers found periodic entertainment in the inspection of scat deposits along the trail. A couple bear piles held only vegetation remains. More interesting were two relatively fresh scats of probably a weasel; one of these held the lower jaw and some molar teeth of a vole. A new hiker discovered an old scat, perhaps of a wolf, containing crunched-up bones and lots of fur.

Bird-listening was good: Wilson's warblers had arrived recently and were out in force. They added their chattery song to the mix of orange-crowned warblers, Townsend's warblers, robins, kinglets, juncos, and winter wrens. A red-breasted sapsucker flew into an alder thicket where all could see it.

A porcupine owned the trail and found it easy walking until faced with a group of two-legged giants. It then decided to retreat up and over a big log and out of sight.

I was pleased to find American dippers nesting again in the landslide-debris dam that creates the large pond near the upper power house. Dippers have nested here for a number of years, in a well-concealed site protected by falling water and lots of boulders. We know of three pairs of dippers nesting along Salmon Creek this year, where they feed not only on the usual aquatic insect larvae but also on small brook trout that were introduced here years ago.

The information sign at the trailhead and the AEL&P brochure about the trail and dam note that the concrete dam was completed in 1914. It is said to be the world's first true constant-angle arch dam. The new design, as of 1914, is said to be particularly good for high, narrow canyons. I was curious to know what the "constant-angle" term meant and, with some references kindly provided by AEL&P, I found out. Another older form of arch dam is a "constant-radius" dam - like a cylinder - with a varying angle between the radii that is smaller near the bottom of the dam. However, that design uses more concrete and costs more money and is not as strong as the then-innovative constant-angle variable-radius dam. If you like little puzzles in the geometry of circles, you can figure out how the constant-angle variable-radius design achieves good strength with less material.

If you do a Google search on constant-angle dams or Salmon Creek Dam, you should turn up some helpful references. If that fails, don't bother AEL&P, but contact me via the Empire.

• Mary F. Willson is a retired professor of ecology.



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