July 30, 2019
Challenge at Glen Canyon
Photo from the Bureau of Reclamation showing plywood extensions at the top of a spillway gate and the permanent installation.
The epic snowpack and runoff year in the Colorado River Basin evokes memories of 1983 and the dangers at the Glen Canyon Dam when the left spillway failed. Reclamation had drawn down the reservoir in anticipation of the runoff but they didn’t have a lot of experience since it was close to the first fill. Also, it started snowing in the late spring in the Rockies above Glen Canyon and it didn’t stop. Many tributaries of the Colorado River were out of their banks by June and all that water was headed to Lake Powell.
Here’s a link to The Arizona Republic’s recap of the early part of the emergency, "For a while in 1983, sheets of plywood were all that kept the mighty Glen Canyon Dam from overflowing”
Above is a photo from the Bureau of Reclamation showing plywood extensions at the top of a spillway gate and the permanent installation.
The left spillway failure was caused by cavitation. Here’s the definition from Wikipedia: "Cavitation is a phenomenon in which rapid changes of pressure in a liquid lead to the formation of small vapor-filled cavities, in places where the pressure is relatively low...When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate an intense shock wave.”
And yes, there were shockwaves, and lots of damage. Here’s a photo from Reclamation as engineers and craftsmen started rebuilding the spillway.
And, cavitation is explained in the video from Awesome Science.
It’s interesting to note that the last time the spillways were used was in 1984, after the repairs were completed following damage in 1983. It will take multiple successive snowpack years like 2019 to again fill Lake Powell.