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Colorado River Study Bad News for Thirsty Californians

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The Colorado River | Photo: U.S. Bureau of Reclamation

The Colorado River isn't likely to have enough water in it to guarantee Southern California its legal share, according to a new report by the U.S. Bureau of Reclamation. That's bad news for Southern California farming communities such as the Imperial Valley, and it's bad news for communities served by the Metropolitan Water District, which takes about 1.2 million acre-feet a year from the Colorado via its Colorado River Aqueduct. That's about a third of MWD's supply.

The report, with the slightly prosaic title "Colorado River Basin Water Supply and Demand Study," predicts that throughout the 21st century, the Colorado river downstream from Lee's Ferry in Arizona will likely average only around 90 percent of the annual flows typical for the period 1950-2000. That's just the average flows: the report also suggests that extreme droughts in the Colorado River Basin will become more frequent.

The Colorado River basin, which includes the large Green River watershed, covers a quarter of a million square miles in Wyoming, Colorado, Utah, Nevada, Arizona, New Mexico, and California, as well as the Mexican states of Sonora and Baja California. There are few bodies of water as altered, contained and legally adjudicated as the Colorado. If you want to get a grounding in the basics of Colorado River water politics, you could do a lot worse than watching the second episode of the documentary "Cadillac Desert," a portion if which is embedded here:


Every drop of the Colorado River's flow in all but the wettest years is designated for someone's use, whether it's ranchers in Wyoming and New Mexico, oil refineries on the California coast, or casino fountains in Las Vegas. That's in a wet year. The Colorado River Compact, the agreement that allocated the river's flow among seven U.S. states and Mexico, was crafted between 1921 and 1944, and apportionments were based on what were then thought to be typical flows.

As it turns out, the first half of the 20th Century was wetter than is typical for the Southwest. Since then, Southern California has often taken advantage of surplus water that the other states didn't have enough development to use.

The Colorado River Compact divides the basin into two sections the Upper and Lower Basins, with the boundary at Lee's Ferry, Arizona, just upstream from the Grand Canyon. Each basin is allotted 7.5 million acre-feet per year. Mexico is supposed to receive another 1.5 million acre-feet per year. An annual discharge of 15 million acre-feet may have seemed reasonable in the 1930s, but from 1920-2010, the average amount of water in the river each year has been about two-thirds that. The Colorado's output has met or exceeded 15 million acre-feet per year only in 17 of the last 40 years.

And even with the Upper Basin not using its entire allotment, at least 15 million acre feet per year has been used most years, with overages from wet years being stored in reservoirs like Lake Powell and Lake Mead.

Which means that the river is already oversubscribed, and a drop in average flows is likely to be a big problem, even disregarding the inexorable pace of development in places like Phoenix.

As the report's executive summary says, somewhat chillingly,

The mean natural flow at Lees Ferry over the next 50 years is projected to decrease by approximately 9 percent, along with a projected increase in both drought frequency and duration.

Most of the river's flow falls as snow or winter rain in the Upper Basin states. 92 percent of all the water in the river falls above Lee's Ferry. A nine percent loss in flows at Lee's Ferry pretty much guarantees a nine percent or greater loss in flows at Parker Dam, where the MWD sticks its straw into the river.

Here's the projection broken down for those sections of the river relevant to California water interests:

gauges-12-13-12.jpg
gauges-12-13-12.jpg

In other words, the MWD is going to need to figure out ways to lessen its demand for Colorado River water, and since -- the blandishments of water project promoters like Cadiz notwithstanding -- there isn't going to be a new source of water readily available to replace the Colorado, that means reducing water use.

This might be a cheap shot, but I have a suggestion, which I'll just imply with this aerial photo of part of MWD's service area.

mwd-12-13-12-thumb-600x300-42050
Laaaaaaaaaawwwwwns | Photo: Google Maps

Chris Clarke is an environmental writer of two decades standing. He writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.

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