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Taking the Long View on the Colorado River

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Morelos Dam, the farthest-downstream dam on the Colorado | Photo: Chuck Coker/Flickr/Creative Commons License

The Colorado River's in the news this week. On Tuesday, the group American Rivers declared the Colorado America's most endangered river, just hours after an agreement to deliver a small amount of water to the river's delta was mentioned in the New York Times. Few rivers have been as massively altered by people along their course. But what does the future really hold for the Colorado?

Without the network of dams and pipelines that harness the Colorado River, the southwestern United States would be very different. 36 million people drink its water. It irrigates crops from Denver to Mexicali that wouldn't otherwise grow. Without water from the Colorado, Phoenix and Las Vegas would likely still be small towns. Los Angeles, itself mostly watered by the Owens River, might still be a thriving city, but it would be surrounded by isolated small towns instead of the sprawl fed by the Metropolitan Water District's Colorado River Aqueduct. Without the Colorado, there would be more than 6,250 square miles of current agricultural land going unirrigated.

The river is so heavily "subscribed," in the parlance of the water engineers -- there are so many legal claims on every drop of water -- that most years, not a single one of those drops reaches the river's outflow at the Sea of Cortez. The Colorado's average annual flow before the era of the engineers is thought to have been about 16 million acre-feet, though there's increasing suspicion that that's an overestimate stemming from a wetter-than-average 20th Century. Most years, only 1.5 million acre-feet or so reaches Mexico, and all of that pittance gets used for drinking water and irrigation south of the border.

That's why the bilateral agreement that made the pages of the New York Times is so important. Referred to by the unlikely handle "Minute 319," the agreement mainly adjusts the details of the 1944 treaty dividing the river's flow between the two countries. It allows Mexico to store "surplus water" -- should there ever be any -- in Lake Mead behind Hoover Dam, which not only helps Mexico plan its water use but lowers the chances that declining reservoir levels will strand Las Vegas' water intake pipes. Minute 319 allows the U.S. to reduce the amount of water flowing to Mexico in drought years.

The provision of Minute 319 that's gotten the news media interested is that the agreement sends 158,088 acre-feet -- less than a hundredth of the river's "normal" output -- to the sea. Two thirds of that will be sent downriver in a "pulse flow" designed to resemble the natural flood regime at the river's mouth, scouring silt out of clogged channels and benefiting local riparian trees like willows and cottonwoods, whose seeds require flooding to germinate. The rest will trickle to the sea in a "base flow" over the next five years.

The water for Minute 319's base flow will come from retired Mexican irrigation allotments bought for the purpose by environmental groups. That's earned it the opposition of the Mexican farmers' group Confederación Nacional de Campesinos, which views the transfer as a threat to Mexican agriculture. The largest U.S. user of the river's water, the Imperial Irrigation District, also opposes Minute 319, though for reasons unrelated to the Delta flows.

Regardless of opposition, the agreement became valid in November, and delta restoration advocates hope the renewed flows for the next five years will allow about 2,000 acres of the Delta's riparian habitat to be freshened up. That's an unarguably good thing, though watery phrases like "a drop in the bucket" come to mind. The Colorado Delta's ecosystem, which includes the probably doomed Salton Sea, is in the free-fall stage of ecological collapse. Its once-thriving estuary, habitat for billions of birds and nursery to the Sea of Cortez's fisheries, is basically teetering on the brink of extinction.

As American Rivers' 2013 report America's Most Endangered Rivers points out, that threat isn't limited to the river's delta. What the group terms "outdated water management" and an increasing likelihood of catastrophic drought threaten wildlife dependent on upstream reaches of the river as well -- and the human communities that use the river's water to boot. In the words of the report:

Climate change is expected to reduce Colorado River's flow by 10 to 30 percent by 2050. Warmer weather, less snow, a reduction in stream runoff, and changed timing of spring runoff are all likely impacts. Currently scheduled water deliveries from the Colorado system are not sustainable in the future if climate change reduces runoff even by as little as 10 percent. With snowpack once again below average, extreme drought conditions will likely persist when water is needed most.

Talking about the Colorado River itself as "endangered" isn't quite right. Individual species and ecological communities that rely on the river, sure. Human societies that have sunk straws into the river, most definitely. It may well be that a hundred years from now, Phoenix and Las Vegas will essentially be ghost towns -- as will California communities such as the cities in the Imperial Valley that are wholly dependent on Colorado River flows for their livelihoods and their drinking water.

But the River itself isn't endangered. It's enchained and encumbered with dams, sure, and every bit of it has been diverted and put to work and occasionally returned to the river bed burdened with effluent. The life-giving silt that once built the Delta is trapped at the bottoms of reservoirs, starving the stretches downstream. The river's very name Colorado came from that silt, which gave the water its historic reddish color. Downstream from the river's huge silt-trapping dams, that river water is now an abnormal green.

All that said, the river's seen worse days, and not all that long ago.

Prospect Falls and Harrington's mountain goat | Painting © Carl S. Buell

That's a painting of an extinct Harrington's mountain goat with Prospect Falls as a backdrop by renowned paleontological illustrator (and my friend) Carl Buell. Prospect Falls isn't there anymore: it's now a series of rapids on the Colorado known as Lava Falls. Lava Falls, at River Mile 179 in the Grand Canyon, is a debris ridge over which the river drops a bit less than 40 feet in a few hundred yards. 1.8 million years back in the Pleistocene that ridge -- the Prospect Dam -- was 2,260 feet higher. A series of volcanic eruptions back then built the Prospect Dam across the river. It took more than 20 years for the River to fill up the lake behind it to the point where water started flowing over the top of the lava dam, at which point the entire flow of the river coursed over a waterfall a dozen times higher than Niagara's -- and with twice as much water, on average. Before that, most of the river's course downstream was completely dry -- for more than 20 years.

Prospect Dam was much more massive than any dam humans have ever built. More than three times the height of Hoover Dam, it was a massive plug of lava. The arch dams on the Colorado these days are delicate little wafers by comparison, and they're built of far less resilient stuff. Once Prospect Falls started flowing over Prospect Dam, it took less than 40,000 years to erode to nothing. 1.8 million years ago it was like two Niagaras flowing over Yosemite Falls. 1.76 million years ago it was gone.

Our dams on the Colorado seem permanent. They aren't. They may remain for another hundred years, or another two hundred. Likely less than two hundred. The dams trap almost all the river's silt behind them, and that silt builds up more rapidly than we'd like. Some estimates hold that silt accumulation could put Glen Canyon Dam out of commission before the end of this century, by clogging the penstocks that discharge water downstream from Lake Powell toward the Grand Canyon. If the penstocks are out of commission, wet years could overtop the dam's spillways.

As Grand Canyon National Park's former Science Center director Dave Haskell writes, that overtopping essentially brings on the Apocalypse for folks downstream:

In wet cycles, because of drastically reduced reservoir storage capacity, the water level could easily reach the spillways. These spillways were not designed for the discharge of water for prolonged periods of time. High volume use of these spillways for more than a week or two would most likely lead to their catastrophic failure. According to BOR [Bureau of Reclamation] studies, over-topping of the dam would likely lead to the formation of a river channel through the soft sandstone on either side of the dam. Considering the tremendous water pressure created by a reservoir of this size and the easily eroded sandstone that abuts the dam, once the spillways failed, complete breaching of the dam could occur in a matter of hours.

Catastrophic complete breaching of Glen Canyon Dam would mean a 500-foot wall of water racing through the Grand Canyon. That flood would lose only about 270 feet in height by the time it reached Lake Mead, with failure of Hoover Dam a not impossible result. At that point remaining dams downstream would fail in relatively rapid succession, popping open like buttons. Laughlin, Bullhead City, Needles, Blythe, Parker, and Yuma would be gone. Imperial County might be as well.

Or Hoover Dam would hold, and flooding downstream be merely staggering, and all the silt entombed in Lake Powell would roll down to Lake Mead to repeat the process farther downstream a few decades hence.

This already almost happened: the Glen Canyon Dam almost failed in 1983 during a wet El Niño year. Dam managers managed to keep the flood from overtopping the dam by -- no kidding -- nailing up sheets of plywood. It's only by fluke that we don't talk about Needles the way we talk about Atlantis.

The River, in other words, will outlive us all. What's endangered are the communities, human and non-, who depend on it. The river's fish and birds and people are in trouble, and unless we learn how to use the River more wisely we're in trouble. But the River isn't. The River bats last.

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