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Scientists Plan for Grand Experiment in the Colorado River Delta

The dry Colorado River Delta against the Cucapá Mountains. Photo by Erik Rochner/National Geographic
The dry Colorado River Delta against the Cucapá Mountains. Photo by Erik Rochner/National Geographic

Once written off as dying of thirst and beyond revival, the delta of the Colorado River is slated to get a rejuvenating flood that for scientists offers a unique opportunity: the chance to study how plants, trees, birds, fisheries, and the vast delta ecosystem as a whole respond to an experimental pulse of river water.

This flood is made possible by Minute 319, the add-on to the 1944 treaty between the United States and Mexico that divides the Colorado River between the two neighboring nations.

Signed in late 2012, Minute 319 allows Mexico to store some water in Lake Mead, the giant reservoir behind Hoover Dam, establishes new rules for sharing shortages in times of drought, and commits the two nations to return some flow to the delta as part of a five-year pilot project.

The Colorado Delta was once one of the planet’s great desert aquatic ecosystems, boasting 2 million acres of lush wetland habitat.  For millions of years, it received a huge spring flood as the winter snows melted in the Rocky Mountains and the resulting flows coursed south.  The flood waters spread across the delta before emptying into the upper Gulf of California.

That yearly flood cleansed the river channel and floodplain, recharged groundwater, aided the reproduction of native cottonwoods and willows, and sustained the overall delta ecosystem and its extraordinary bird and wildlife habitat.  It also connected the Colorado River to the sea, where fisheries depend on the mixing of saltwater with fresh water for their spawning and rearing grounds.

But the construction of big dams and river diversions during the 20th century siphoned off the river’s flow, leaving little or none for the delta in most years of the last half century.  Wetlands have shrunk to about 10 percent of their former area, and fish, birds and wildlife have declined dramatically.  The native Cucapá, who fished and farmed in the delta for at least a thousand years, have lost their way of life.

The last time the delta enjoyed a significant influx of fresh water was in the late 1990s, a period of unusually high precipitation in the Colorado watershed that resulted in “surplus” water passing through the basin’s dams, across the international border, and on to the thirsty delta in northwestern Mexico.

Writing in this week’s issue of Eos, a publication of the American Geophysical Union, seven scientists who have collectively clocked decades of research in the Colorado Delta note that those 1990s flood pulses “demonstrated the resilience of the riparian zone and gave hope for its potential restoration, should a regular supply of water be found.”

Minute 319 calls for a flood pulse of 105,392 acre-feet (130 million cubic meters).  The water will be released from Lake Mead at Hoover Dam, and then, mimicking the historic natural flood, will flow south to the delta.

Compared with the pre-dam spring flood of some 15 million acre-feet, this pulse appears paltry. But the delta scientists expect it to be sufficient to flood low terraces and backwaters, move channel sediments, recharge groundwater, and promote the germination of native cottonwoods and willows, which create prime habitat for birds.

Last February, a National Geographic team and I traversed parts of the delta with Osvel Hinojosa Huerta, an ecologist with the Mexican conservation organization ProNatura Noroeste and a co-author of the Eos article.  We visited a local nursery that was growing young cottonwoods, willows and mesquite, native trees that are being planted along the river channel and in wetland restoration sites.  The anticipated spring flood will help them get established and reproduce.

Teams of scientists from both sides of the border are collecting pre-flood baseline data and, after the flood, they will track the immediate and longer-term effects on the delta’s vegetation, birds, wildlife, and other ecosystem attributes.

The hope is that beneficial results, and the potential for more, will lead the two countries to expand the restoration effort beyond this pilot period and establish a longer-term commitment to revitalizing the delta.

The experimental spring flood offers a rare scientific opportunity, to be sure.

But even more important, it is a crucial step toward restoring a great aquatic ecosystem, and shows the power of political and scientific cooperation in solving our water problems.

To learn more, click here to see our National Geographic videos, blog posts and photo galleries of the Colorado Delta.

[Note: I edited this post about ten hours after publication to remove reference to the timing of the experimental flood, because formal approval of the date has not yet been given.]

Sandra Postel is director of the Global Water Policy Project, Freshwater Fellow of the National Geographic Society, and author of several books and numerous articles on global water issues.  She is co-creator of Change the Course, the national freshwater conservation and restoration campaign being piloted in the Colorado River Basin.

Comments

  1. Bob Batchelder
    Nashua
    January 6, 8:31 am

    Has California signed off on this? Why would they ever allow such a release of “their” water in Lake Mead when the lake level is already dropping due to the ongoing and projected drought?

  2. Mark
    New England USA
    December 24, 2013, 9:52 pm

    I just read this article tonight on Christmas Eve… what an outstanding gift to the region and both nations! I wish the scientists every success in their endeavor, have they studied the possible introduction of more hardwood tree growth along the river to promote an increase in compost material to help to enrich the soil over time to possibly help sustain the plant life during drier periods?

  3. jay
    Muscat
    December 22, 2013, 7:24 am

    If sociopolitical cooperation of this kind sweeps the world, in the interest of the planet earth, then the boundaries between nations will become redundant, and ecosystems will flourish everywhere.Truly a positive piece of news.

  4. Eloise Kendy
    Helena, MT
    December 12, 2013, 11:36 pm

    Hi Sandra! As always, you have compellingly reduced complex science into its essence. Just one point, though: there is but one binational science team, not separate teams on each side of the border. Representing The Nature Conservancy on that team, I am thoroughly enjoying both a cultural and a scientific experience of a lifetime, for which I am extremely grateful. To the river! — Eloise

  5. GUILLERMO MARTINEZ
    México
    December 12, 2013, 3:10 pm

    where can i find more information on this theme? thank you very much

    • Sandra Postel
      December 12, 2013, 3:30 pm

      Please check out the links in the post, as well as the links to our videos and blog posts at the end of the piece. Thank you for writing. – Sandra