By Sid Perkins
Last November, the Grand Canyon experienced its largest flood in more than 8 years. For nearly 4 days late that month, flow rates along the Colorado River swelled as much as 20 percent above typical peak flows. The massive inundation, rather than resulting from the series of storms that had soaked the region for months, occurred when engineers at Arizona’s Glen Canyon Dam cranked open the floodgates to send extra water downstream.
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The planned flood, designed and scheduled by scientists, was intended to rebuild the sandbars and beaches along stretches of the river near the dam. In the 4 decades since the massive dam was built, those river features have been, on average, losing more material than they gain. That’s because this now-tamed stretch of river carries much less sandbar-building sediment than it did before the dam was built.