Author:
Dmitri
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Date Posted: 19:41:21 04/07/13 Sun
>Thanks for sharing the link to the pictures. I find it
>ironic that the government is taking this action to
>undo the problems they created by damming the river in
>the first place.
Well, damming the river basically made it runnable. Except for very short periods between extremes, the river, like most desert rivers, was either quite high or low, way up in flood or bottom-scraping practically unrunnable, especially in the craft of choice, large rafts. Now it is runnable year around.
What the government is doing here is trying to make it look like they're attempting something to help mitigate the mistake made before. It can't help, though. Water moves the sand downstream. That's all it does. In these small floods they're doing, more sand moves downstream. In large floods (which don't happen anymore), a lot of sand moves downstream.
The government claims the sand coming into the Grand Canyon is about 10 percent of pre-dam levels. Personally I doubt that it's that high. Maybe 5 percent? Probably more like 1 percent. It would depend on where you measure it. Basically zero measured at Lee's Ferry, maybe 10% measured at the backwaters of Lake Mead (near the end of the Canyon, and I still think it's less than that).
The upper reaches (above the Little Colorado River at mile 64) basically have no significant source of sand other than the Paria (pronounced Puh-REE-uh) River, which is tiny. The sand in the lower Canyon has migrated down from the parts upstream (but still from below the dam). Some of it is new sand, that 1% to 10% guestimate figure.
Sure, there's sand on the bottom that can get stirred up and placed on beaches when the river level is brought up, but there's not much there, especially in the upper reaches, and what there is is just getting swept downstream. It was accomplished pre-dam because there was more coming down from above to replace what was lost to downstream. Think of it as waves of sand migrating downstream with each flood with little to no new sand to replace it. All that's happening is that it's hastening the movement of the sand from in the river part of the Canyon into the upper parts of Lake Meade.
Dmitri
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