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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.

Manmade floods can't do much about the water clarity and temperature from Lake Powell. The silt on the lake bottom could be excavated and trucked around the dam or sluiced through a new pipeline, but at a cost of hundreds of millions of dollars.

The only significant natural deposits of silt coming into the Grand Canyon today are mainly from the Paria and Little Colorado rivers. They account for only about 10 percent of what the pre-dam Colorado River used to receive in sand and silt, but it will have to do for now.

The plan is to wait until late fall and spring, after the monsoon and spring snowmelt seasons on the tributaries, then release enough water to replenish beaches, which naturally erode from river currents and storms.

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Scientists and conservationists like the idea of at least partially restoring some of the seasonal floods in the Canyon. They've been calling for them for decades, along with more constant daily flows that mimic the former rhythms of the river, not the late-afternoon surges in summer to power the air conditioners in Las Vegas and Phoenix.

And rafters will benefit from more beach camping sites, although the locations may change after each 5-day flood.

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Fishermen may see fewer rainbow trout -- the plan is to remove them from the Colorado and restock them elsewhere. But perhaps that will put more of the "sport" back into the sports fishery at Lees Ferry.

As for the power companies, because the dam's generators are bypassed during a high-flow release, they will lose about $122 million in revenues over 10 years.

But that is a mere trickle compared with the tens of billions of dollars in revenues they receive from Glen Canyon electricity over the same period.

Will the floods restore the Colorado ecosystem in the Grand Canyon to its pre-dam state? Of course not. A new ecosystem has replaced the old one, and the floods and fish removal can only modify it in ways that support some of the pre-dam conditions.

It has taken 16 years since the first experimental flood to get all parties on the same page regarding a more frequent, long-term intervention plan. Now it's time to get started and see if it works.

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