Grand Canyon Blow Out.

March 6, 2008 4:26 PM

The U.S. government flooded the Grand Canyon yesterday in the hopes of restoring the ecosystem. Some environmentalists disagree.
posted by gman (34 comments total)

Yeah, huh.

Why do I get the feeling they'll just be flushing the ecosystem away?
posted by Sys Rq at 4:34 PM on March 6, 2008

The government is in charge of flood control at a treasured resource? What could possibly go wrong?
posted by Saucy Intruder at 4:39 PM on March 6, 2008 [6 favorites]

It's funny how the YouTube video introduces it as "rare footage" when it's from the Associated Press, arguably one of the most prominent news organizations in the entire world.
posted by dhammond at 4:40 PM on March 6, 2008 [2 favorites]

I hope it wasn't Spanish Galleons full of water. That would be just awful
posted by mattoxic at 4:41 PM on March 6, 2008 [1 favorite]

Some environmentalists disagree.

That's a bit misleading. The environmentalist are arguing for more frequent floods. A little more detail about the environmental issues.
posted by ssg at 4:47 PM on March 6, 2008

Glen Canyon Dam is America's biggest planned mistake, besides above ground nuclear testing. The mistake was to build an online dam, instead of an offline dam aside the river system. The reservoir will silt up soon enough, and we'll rename it Glen Canyon Waterfall, until it erodes away.
posted by Brian B. at 5:00 PM on March 6, 2008

IANA geologist, but doesn't it take a (relatively) long time for these sandbars to naturally accumulate, long enough for ecosystems to naturally evolve there? It seems to me that they'd be making these weak sandbars that'd be eroded away (relatively) quickly.

IANA conspiracist, but this smells to me of them just wanting to flush all the sediment out that's mucking up the dam, and spent $80M to bolster that decision.

(Well, that's a little far fetched. but... what Saucy Intruder said.)
posted by not_on_display at 5:03 PM on March 6, 2008

Why do I get the feeling they'll just be flushing the ecosystem away?

The plants and animals that make up the ecosystem (at least the one that existed before the dam was built) were adapted to frequent flooding. You might as well ask if the Arctic is too cold for the polar bears.
posted by ssg at 5:09 PM on March 6, 2008

But how does the sediment from above the dam get through? I realise that some of it will be held in suspension in the water, but doesn't sediment movement/relocation come mainly from being dragged along the bed of the river from bank erosion and soil run off?

If those pipes aren't sucking straight from the lower part of the reservoir, they can't possibly mimic the sediment flow from flood from the upper reaches of the river. They'll just make a mini sediment element as it will be just water going through.

The 'more regular flooding' argument seems to be very sensible to me, as well as some attempt to transfer sediment past the point of the damn other than trying to fire it out of big tubes. It does rather smack of 'for the convenience of the water company with some environmental tag words added' to me. Especially with this quote for reactions to criticism and claims of not including all the information in the report supporting the flood:

Lawyers with the department of the interior battled to make Martin withdraw his comments to the review, fearing that a finding of "significant impairment" would lead to additional reviews, effectively blocking the plan.

That doesn't sound like "Our report has not at all been slanted" at all to me... But I am an old cynic.
posted by Brockles at 5:22 PM on March 6, 2008

But how does the sediment from above the dam get through?

The floods predominantly redistribute sediment already in the canyon, but which is not spread throughout the river as it would have been during normal flooding cycles. I spent 16 days on the river in 1997, with some folks who had also been on the river in 1995 (and had previously guided on it, so were very familiar with the topography). They said the flooding made an appreciable difference.
posted by OmieWise at 5:45 PM on March 6, 2008

The related videos of the 1983 flooding are interesting. Are they allowing white water rafting this time too?
posted by tellurian at 5:51 PM on March 6, 2008

I understand that, and I'm not at all saying the floods are useless, just only part of the issue. Before the dam was built, there would have been a flow of sediment from however many miles of river are upstream. Redistributing the sediment won't replicate the natural function of the original flooding fully, as there will be no replenishment with additional sediment from above the dam.
posted by Brockles at 5:51 PM on March 6, 2008

I realise that some of it will be held in suspension in the water, but doesn't sediment movement/relocation come mainly from being dragged along the bed of the river from bank erosion and soil run off?

The USGS claims that sediment that there is already a good amount of sediment below the dam that is stuck on the bottom of the river. Much of the sediment that sits on the bottom of the river is from tributaries that enter the river below the dam. This sediment settled out there with the lower water velocities (due to the lower flows below the dam). When higher flows go through the dam, the sediment is picked up by the faster moving and more turbulent waters of the flood and then settles out in areas that are naturally slower moving or more likely to trap sediment (e.g. sandbars at corners on the river).

You can read more about it on the main USGS page about previous floods. It certainly is the case that much of the sediment from upstream of the dam settles out in the reservoir, which is a pretty common problem. I guess the argument would be that it is better to have some flooding to better distribute the sediment that is below the dam rather than none at all.

By the way, that USGS page actually gives the important piece of information that is missing from all news articles: the turbines in the dam can handle 33,200 cubic feet per second and the flood is 41,500 cfs, so the flood costs somewhere in the (very rough) vicinity of $1M worth of lost power, plus the additional cost of generating extra electricity now when demand is relatively low, which would probably increase that figure significantly.*

* Fun fact: Some hydroelectric dam operators occasionally have to pay others to take their electricity for short periods when they have to maintain minimum flows for environmental or other reasons.
posted by ssg at 6:05 PM on March 6, 2008 [1 favorite]

They're just trying to hide the evidence of the canyon's true age so creationist museums continue to draw crowds.
posted by pmbuko at 6:06 PM on March 6, 2008 [1 favorite]

IANA geologist, but doesn't it take a (relatively) long time for these sandbars to naturally accumulate

Nope. Bars are built by extreme events and a really good flood can easily put several feet of sediment onto a bar. Or on top of a bridge!
posted by fshgrl at 7:48 PM on March 6, 2008

I'm going to paint the sidewalks on my street a rich green and pretend that it's a grassy field. Then the animals will come back.
posted by chococat at 7:50 PM on March 6, 2008 [1 favorite]

I was kayaking the Canyon during the last controlled flood in 2000. The flow went from 8000 cubic feet per second to over 31,000 cfs in just a few hours. Raft boatmen had to sleep on their rafts that night in order to periodically pull in their boats as the water level went up about five feet. The results were dramatic. Over a couple of days huge new beaches and sandbars were rebuilt that had been missing for years. The sediment primarily comes from the bottom of the river bed where it accumulates between floods. The water from just below Glen Canyon Dam is abnormally clear because the water comes from near the bottom of the dam after all the upstream sediment has settled out. The water is also abnormally cold because it comes from the bottom of the reservoir instead of being warm surface water. This changes the species of fish and other aquatic life in the river. There is lots of sediment to redistribute from the river bed because of side streams that feed the Canyon, but it requires floods to move it up on the banks. The Paria River enters just a few miles below the dam and changes it from clear green to the reddish brown that gives the river its name. Much more sediment enters from the Little Colorado River downstream. The Glen Canyon Dam is truly a tragedy that David Brower of the Sierra Club conceded to in an effort to save the lower half. It was a mistake. The Colorado River and the Grand Canyon is the finest wilderness canyon in the western hemisphere and unfortunately half of it is buried under water. It is now 277 miles long.
posted by JackFlash at 8:09 PM on March 6, 2008 [3 favorites]

Remember that the "Government" isn't some magic entity. It is made up of you and me. And when it comes to the environmental treasures, it is governed by idiots as well as good people.
posted by tomplus2 at 8:21 PM on March 6, 2008

I just hope they remembered not to put anything sharp in the raft after opening Flood Control Dam #3.
posted by substrate at 8:47 PM on March 6, 2008 [1 favorite]

I'm going to paint the sidewalks on my street a rich green and pretend that it's a grassy field. Then the animals will come back.

cargo cult... animal husbandry? cool.
posted by joeblough at 8:53 PM on March 6, 2008

also, i think i remember from the last time they did this that there was some argument against it due to the water coming from the bottom of the dam being extremely cold, and thus nothing like a natural flood. in other words, it might be more detrimental to the native species due to the low water temperature during the flood.

but who knows, its a very complex system, and to pretend that everything will be okay by mimicking nature is pretty naive. the fact is that the river is dammed and it will never be the same as it was.
posted by joeblough at 8:55 PM on March 6, 2008

Hayduke lives
posted by hortense at 9:55 PM on March 6, 2008 [1 favorite]

"This gives you a glimpse of what nature has been doing for millions of years"

And it only took us 40 years to fuck it up. Go Humans!
posted by jontyjago at 1:24 AM on March 7, 2008

Some environmentalists disagree.

Sort of goes without saying, doesn't it?
posted by Kirth Gerson at 3:45 AM on March 7, 2008

Bars are built by extreme events and a really good flood can easily put several feet of sediment onto a bar. Or on top of a bridge!

That's not the point, really. There will be a step loss of sediment because it is not broughht down from above the dam and can't get past it. Of course a flood will move all the sediment around, but the argument that is somehow makes up for the dam being there and they've 'fixed' the affects of building it is a lie. It's adding a nice little environmental feather in their cap that doesn't belong there.

Over a couple of days huge new beaches and sandbars were rebuilt that had been missing for years.

I'd wager their rate of decline would have been much less if they were able to be constantly replenished (with and between floods) by sediment constantly moving past from the upper reaches.

People seem to be disagreeing as if people have said that the flood would not make a difference - of course it will, and no-one has said it doesn't do anything. But what I am saying is that it doesn't do what they say it does. Only part of it. Perhaps if some sort of measure to drop sediment over the top of the dam regularly (with a big chunk at around flood time) would be a better solution and a more accurate model.
posted by Brockles at 5:02 AM on March 7, 2008

Very interesting and educational discussion on a topic about which I know nothing.
posted by rickh at 6:18 AM on March 7, 2008

People seem to be disagreeing as if people have said that the flood would not make a difference - of course it will, and no-one has said it doesn't do anything. But what I am saying is that it doesn't do what they say it does.

I disagree. I understand what you're saying are the limitations of this approach, and I agree with you wholeheartedly. I don't think anyone is seriously suggesting, though, that this kind of flooding is the same as a free flowing river. The dynamics here are quite clear, and no one is suggesting that silt from above the damn is now available downstream because of this flooding. If that's the measure of success, then this is a failure. But that measure of success makes no sense.

The differences between dammed rivers and free-flowing rivers are stark, and the riparian ecosystems are very different. The only way to make the Colorado act like a free-flowing river is to remove the dam.
posted by OmieWise at 7:33 AM on March 7, 2008

On the wall in front of you is a group of buttons,
which are labeled in EBCDIC. However, they are of
different colors: Blue, Yellow, Brown, and Red. The doors
to this room are in the west and south ends.

Now what was that sequence to open up Flood Control Damn #3 again?
posted by The Bellman at 7:54 AM on March 7, 2008

Not "Damn", "Dam". Damn.
posted by The Bellman at 7:55 AM on March 7, 2008

I'd wager their rate of decline would have been much less if they were able to be constantly replenished (with and between floods) by sediment constantly moving past from the upper reaches.

Bars only get replenished during floods Brockles. The sediment has to be carried there by relatively fast moving water and the only time that gets as high as the top of a bar is during a flood.
posted by fshgrl at 8:28 AM on March 7, 2008

Yeah, but my point was that there is a finite amount of sediment, and once it is moved down onto the sand banks, how does it actually replenish anything next time? It's always a game of diminishing returns.
posted by Brockles at 9:42 AM on March 7, 2008

Remember that the "Government" isn't some magic entity. It is made up of you and me.

If that's true, we might be screwed. I don't know shit about ecology or flood control, so I hope like hell you do.

Now, what lever am I supposed to pull to make the water go fast?
posted by quin at 10:12 AM on March 7, 2008 [1 favorite]

Yeah, but my point was that there is a finite amount of sediment, and once it is moved down onto the sand banks, how does it actually replenish anything next time? It's always a game of diminishing returns.

I think you're operating from the wrong model. You seem to be assuming that the Canyon is a closed ecosystem with regard to sediment. While it's true that none of the sediment from above the dam will ever be below the dam, sediment is replenished in the Colorado all the time from tributaries and monsoons. The Grand Canyon is literally chock-a-block with side canyons that all dump sediment into the Colorado during the rainy season. But, that same sediment tends to settle out over differently under normal flow conditions than it does during a flood. During this flood, sediment is picked up and redistributed. In the fall, more sediment will enter the canyon at a thousand different points. It will be redistributed then next time they do a controlled flooding.

This map at the LOC shows all the many side-canyons that empty sediment into the Colorado every year during the rainy season. There are literally thousands, many dry until the rainy season, some that flow year-round. The flooding is designed to redistribute the sediment loads from these side-canyons.
posted by OmieWise at 10:37 AM on March 7, 2008

Yeah, but my point was that there is a finite amount of sediment, and once it is moved down onto the sand banks, how does it actually replenish anything next time?

No, there isn't a finite amount of sediment. Every rain storm washes immense amounts of sediment into the river. In fact all of the hundreds of rapids on the river are formed by washouts from the local side canyons, not from upstream. Most of the sediment is relatively local. It doesn't come from hundreds of miles upstream in the Rockies where the rock is harder and the terrain covered with vegetation. The sediment comes from the soft rock in the canyon and its bare desert terrain. The Paria and Little Colorado River tributaries contribute large amounts of sediment within the canyon. The Little Colorado tributary sediment year round is so thick that you can hear it as it sandblasts the bottom of your boat. It sounds like frying bacon.

Between floods, the eddies and hollows in the stream bed fill with sediment. Once these storage reservoirs are filled, any extra sediment is simply washed downstream and out of the canyon. At that point, extra sediment from above the dam wouldn't contribute to more sediment storage since the tanks are already filled. During a flood, the sediment is scoured from the stream bed storage areas and deposited on the banks forming bars and beaches. After the flood, over a period of years, the bank sediment is washed back into the stream bed, requiring a new flood.

The dam means that the sediment storage is replenished a little more slowly and that big floods that move the sediment to the banks are less frequent. The same process continues as before the dam although at a lower pace.
posted by JackFlash at 11:02 AM on March 7, 2008