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hatrack

(59,439 posts)
Fri Jan 25, 2013, 02:16 PM Jan 2013

As In Prior Trials, Glen Canyon Artificial Flood Boosts Grand Canyon Sandbars, But For How Long?

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Glen Canyon Dam blocks most of the sediment carried downstream by the Colorado River. Among the few remaining sources of sand is the Paria River, which flows into the Colorado about 15 miles below the dam and dumps, on average, about a tenth of the sand that the undammed river used to wash into the Canyon. The flood experiments are meant to find out how to make the best use of it.

Schmidt’s staff has reviewed snapshots from remote digital cameras that showed more than half of the monitored sandbars and beaches — 18 — grew substantially after the November flood receded. Twelve sites showed no change and three eroded substantially. “Every time we do a flood, it builds sandbars,” said Paul Grams, a U.S. Geological Survey research hydrologist. “We know the floods build the bars, and they tend to erode in the six months to a year following the floods.”

The Canyon’s chub numbers have grown threefold, to 12,000 over the past two decades, biologists at this week’s meetings estimated, perhaps aided more by warmer water spilling from a low reservoir. Some river advocates have argued that only frequent artificial floods can approach pre-dam conditions — a possibility that the U.S. Interior Department set up by stripping environmental red tape from experimental releases for the next decade.

But others want more drastic action. “It’s not working,” said John Weisheit, conservation director for Living Rivers, a non-profit organization dedicated to Colorado River conservation. The dam blocks too much sand, and the government should either breach the dam, transport sand around it or give up, he said.

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http://www.azcentral.com/news/articles/20130124feds-grand-canyon-flood-success-beaches-habitat-restored.html?nclick_check=1

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