Editorial from 11/21 Arizona Daily Sun:
Twice-yearly manmade floods on the Colorado in Canyon long overdue
This week’s flooding of the Colorado River below Glen Canyon Dam is different than the floods of 1996, 2004 and 2008.
It won’t be years until the next one takes place.
That’s important because the manmade floods are supposed to simulate the periodic deluges that washed through the Grand Canyon before the dam shut off the natural flow nearly 50 years ago.
Back then, the floods generated by snowmelt and monsoon rains far upstream contained silt and sand that was deposited above normal high water marks. That created beaches and back eddies that were spawning grounds for native fish like the humpback chub.
But after the dam, not only were there no more major floods in the Canyon, but 94 percent of the silt was deposited in Lake Powell. The water that was released below the dam was clear and cold, ideal for nonnative rainbow trout, which preyed on the warm-water chub.