|A Diamond Expeditions boat in Crystal Rapids, 1983|
Photo by J. David Rogers, from here.
Two of the rapids, Crystal and Lava Falls, are rated a 10 on a scale of 10. Crystal (photo) was formed in 1966 when a debris flow from the tributary, Crystal Creek, temporarily dammed the river. Discharges into the Grand Canyon have been regulated by Glen Canyon Dam since 1963, ranging between 5,000 and 30,000 cubic feet per second (cfs). These discharges sculpted the debris fan and widened the channel, but Crystal remained a difficult rapid for boating and was the site of many flips of rafts.
In 1983 rapid snow melt from the Rocky Mountains forced engineers at the Dam to release extra water through the spillways and bypass tubes. Discharges ramped up to 90,000 cfs, and a huge wave developed at Crystal. Why Crystal and not the other rapids? Because the other rapids had, over geologic time scales of thousands of years, seen annual floods in excess of 100,000 cfs and had been sculpted to accommodate these discharges. Not so at Crystal because of the control of Glen Canyon Dam.
The wave that developed was more than 15' high (see photo--the pontoons on the sides of the boat are 3' diameter for scale), and a boat, not as lucky as this one, flipped in the rapids. People were washed up to 15 miles downstream in the frigid waters and one person died. Another died in 1984 in a similar accident although the wave was not as big as pictured here.
A detailed discussion of this wave is in:
Well, fortunately, this is 2011. And, yours truly is off to go rafting!! There's no communication with the outside world once we launch on the river, so, folks, "adios" until mid-May!!
Here's the Bureau of Reclamation update on the Dam operations for April and May: