As Lake Powell Falls, Cataract Canyon's Rapids Begin To Reemerge From 40 Years Of Mud & Silence

[hatrack]

One of my environmental obsessions for decades has been the fate of Glen Canyon, arguably the most beautiful place on the planet before much of it was obliterated in 1963, drowned by the river that carved it once the diversion gates on Glen Canyon Dam closed. If you'd like to get a sense of what the place was like during the Predambrian era, these photos and many more from the Glen Canyon Institute tell the story better than I ever could:

https://www.glencanyon.org/glen-canyon-before-lake-powell-album-4/

Upstream from Glen is Cataract. It's famous as a whitewater run, and in high runoff years its rapids approach or exceed even those in the Grand Canyon - as you'll see in the video:

This sequence is 2/3s of The Big Drops - Satan's Throne and Satan's Gut (Satan's Gut is the bit where the rafters in the video get dumptrucked near the end). And for years, after dropping 30 feet in less than half a mile, that was the end the line. More than half of the 50-odd rapids in Cataract were drowned by the dam, starting just below The Big Drops. They were buried initially by water, and eventually (and inevitably) by silt.

Just as a river entering the sea forms a delta, a river entering a reservoir does the same. The current slows down, and as it slows down, the mud and debris and sand it's been carrying fall out to the bottom of the channel. And as silt builds up, it spreads not just forward with the remnants of the current, but backwards as well. It's called headward aggradation, and over decades, the famously silty Colorado River pushed mud backwards to bury much of Cataract Canyon. Powell was at or near maximum elevation in the early through mid 1980s - 3700' above sea level or near that, but even as it fell during decades of drought, the silt remained. River travelers today drift for miles downstream of the last rapids towards the top of the reservoir between hardened banks of silt 10, 15, 25 feet high, mile after mile.

But now, with Powell dropping below 45% of capacity and 110 feet below maximum elevation, legendary rapids like Gypsum and Imperial are back, the silt and debris finally scoured away by time and drought. Even Dark Canyon Rapid, well downstream, is starting to at least stir the waters. So far, this scouring process has only covered about 5-6 miles of the river, but there's likely more to come for years as springtime peak flows keep carving away at what the reservoir left behind.

And, there's now somebody who's tracking the changes, comparing historic photographs and even enlisting some help from USGS to scientifically track what's going on. The website is just getting up and running, but there's already a lot of interesting information on board.

As I've told non-river rats for years even on meandering Ozark float streams, "Never underestimate the power of moving water."

True enough!

https://www.returningrapids.com

[AllyCat]

1. This is fascinating

As a college student, we heard about all the spring break trips here and everyone rented houseboats and cruised around. We wanted to go but just camped. As soon as I saw the Lake, it looked all wrong. It wasn’t supposed to be there. This was in the mid-80s, 25 years after it was flooded. I never went back.

People on campus talked about Glen Canyon dam all the time, but no one listened. I hope they are listening now.

[hatrack]

2. And here's a presentation by the three guys working on this from YouTube

If you're a river/geology geek, this is the video for you!