The "Boxley Blowout" is where the City of Seattle's Cedar River reservoir leaked in 1918, and washed away the hamlet of Edgewick two miles down Boxley Creek. There is a long series of events leading up to this, which for now I will summarize as follows.
- More than 12,000 years ago (probably several times): a glacier came UP (!!) the Snoqualmie Valley, forcing the Cedar River out of its former course into the Snoqualmie Valley and into a new channel west towards Maple Valley. The old channel is filled with a huge gravel embankment. - 1910: Construction of the Masonry dam is authorized. Two geologists called in to check the adequacy of the dam site express reservations about the gravelly embankment that would form the north side of the future reservoir, and suggest that further study be made. - 1912: Controversy! The City Council is forced to convene a board of engineers to study the matter. Their report says that the notion of sealing the embankment is a fallacy, that there is a better and cheaper location upstream, and recommends suspending construction pending a thorough investigation. But the City rejects their report, having already started building the dam, and not wanting to bear the cost and delay of starting over. - 1914: The dam is completed, and filling of the reservoir starts. Oops--it leaks!. - 1915: And Rattlesnake Lake rises to flood Cedar Falls (Moncton). (See scathing comments.) - 1915-1918: Sealing of the north side is attempted. - October, 1918: Sealing is completed, and pronounced a success. Filling of the reservoir is tried again. - December 23, 1918: Oops.The Seattle Daily Times carried the first report ( "Lumbering Community Desolated") that evening, and a follow-up report the next morning. However, the Post-Intelligencer's article ( "Reservoir Waters Sweep Valley Town") is fuller, and definitely more interesting.
In the following week Seattle's two main newspapers (the Seattle Daily Times and the Post-Intelligencer) carried the following articles:
The P-I also carried a statement from several city councilmen that the Masonry Dam was "Standing As Firm As Gibraltar", that the devastation reported was due to a small wooden dam at Edgewick giving way, and that the alleged break in the embankment "is more than a mile north of the new masonry dam" (gee, I guess there isn't any connection then). Quite a self-serving statement. The P-I accompanied this with a statement ("A Few Facts...") that there was nothing wrong with the dam itself--just the site.
Both papers were scathing in their editorials. The P-I (Dec. 24, "The Cedar River Basin") said "there is no practical way to make a water container out of a sieve", and said the "the project is a repeatedly demonstrated menance, costly alike in the efforts to render it safe and in the payment of damages resulting from the floods." The Times (Dec. 27, "A White Elephant on Our Hands") laid into the councilmen who tried to be engineers, suggesting their prompt retirement from public life. (Something that ought to be looked into.)(Unfortunately, it appears that it was Superintendent Ober, who alone dissented from the "party line", who eventually lost his job.)
(There are additional articles if you want more details.)
It has been estimated that between 800,000 to 2,000,000 cubic yards of detritus was removed in less than two hours. A concern of the engineers at the time was whether the leak was going to cut back into the reservoir and release the water there for a much greater flood, one that would have undoubtably caused much loss of life.
In the lawsuits that followed the City maintained that the burst and subsequent flooding was due to "spring freshets" the night before. (The City lost, and eventually paid over $300,000 in damages.) But careful observations for many years have shown that the flow from the blowout (it still leaks!) varies as the height of the water in the pool immediately behind the dam. And the dam has had a notch cut into it so the reservoir can't be raised to the level originally intended.
A modern report (William Bliton, 1989; not yet on-line) concluded that:
The Masonry Dam never operated as initially designed, primarily because of seepage from the Masonry Pool. The Masonry Dam illustrated the results of selecting a dam site with almost total disregard for local geologic conditions and for the advice of individuals who were skepetical of the suitability of the project siting and the lack of sufficient site exporation--which was completed only after project construction and the subsequent development of seepage.After the fact, knowing that the reservoir leaked in a most dramatic manner, it is easy to point to where the experts said it would leak, and then wonder why the City went on anyway. But the issue is not so much that it leaked (they expected that, and thought they could deal with it), but that it leaked so seriously. After all, even the experts did not predict the Blowout, or even that Rattlesnake Lake would flood Cedar Falls. But they did give warning, and the City proceeded anyway, and quite haphazardly. Considering how much money was spent on this project, how much damage was incurred (and had to be paid for), and that there was a prospect for an even greater disaster, and that all of this could have been avoided, it definitely warrants further study. In the mean while, peruse the articles yourself and see what you think about it.
The Blowout is readily visible from the Rattlesnake Ledges and Little Si, especially in the spring and fall when the deciduous trees in the Blowout contrast strongly with the coniferous trees around it. Look just to the southwest of Cedar Butte.
The Blowout can be visited on the Cedar Butte trail.