A progress report on the Colorado River pulse

Researchers are sifting through the impacts of last spring’s release.


It’s been nine months since a coalition of scientists, water managers and lawmakers from the U.S. and Mexico opened the Morelos Dam at the Arizona border, releasing a massive, one-time pulse into the parched Colorado River Delta. The Colorado is lifeblood to seven states and has failed to reach the ocean since the 1990s, due mainly to over-allocation to a growing population; the pulse was an attempt to revive a much-struggling ecosystem. And despite much fanfare, most of the 70-mile stretch — where 107,000 acre-feet of water either swept across desiccated stretches of the channel or sank into the soil where the existing water table was healthier and closer to the surface — dried up within weeks.

In general, the pulse has jumpstarted native vegetation and acted as scientists expected: like a spring flood would if the river were healthy. But experts warn not to get too excited quite yet, before all the data’s analyzed. This week, researchers are giving a progress report of environmental changes they’ve seen at the delta since last spring’s release.

Photograph of the Colorado River Delta from above, by Francisco Zamora.

Among the positive stories, for example, was a change in overall greenness. Satellite images beginning in 2000 have shown a decrease in delta vegetation, but over the last nine months, scientists have seen a 23 percent uptick in greenness. Karl Flessa, a professor of geosciences at University of Arizona and co-chief scientist of the monitoring program, says some of that new growth is invasive salt cedar, a competitor of the more desirable cottonwood and willow. But still, it’s progress. Flessa says some kind of vegetation rest stop, even if it’s invasive, is better than nothing for birds migrating between Central and North Americas. 

Francisco Zamora, director of the Colorado River Delta Legacy Program at Tucson-based environmental nonprofit Sonoran Institute, says he was somewhat underwhelmed by the amount of inundation as a result of the pulse. The institute oversees the Laguna Grande restoration site in Mexico. “I want to say about 60 percent of what we thought would be inundated was,” Zamora says. And yet since the experimental flow, the site has made significant progress with native vegetation. Zamora’s team collected native seeds and sprayed them onto wet soil — in a process known as hydro-seeding — just before the release. Their hope was that the flow would raise the underground water table and keep surface soil wet long enough that seeds would germinate with roots deep enough to hit the table. Zamora says the hydro-seeding is working. Since the pulse, willow and cottonwood saplings at the Laguna Grande have sprouted, some as high as six feet.

Daniel Chavez planting a willow seedling in Laguna Grande, a restoration project run by the Sonoran Institute in the Colorado River Delta, Baja California, Mexico. ©Bill Hatcher 2014
According to the progress report, “Minute 319 Colorado River Delta Environmental Flows Monitoring,” the water tables rose along the entire stretch of the river, from the Arizona border to the Gulf of California. They also lowered in the weeks following the pulse, but Flessa and Zamora say that mimics natural cycles of spring floods. Whether the water would recede wasn’t the big question on everyone’s minds, but rather the speed at which the tables receded: If tables shrink too quickly, seeds don’t have a chance to germinate. In the Laguna Grande restoration area, scientists used additional base flow from Mexican irrigation canals to keep levels high even after the pulse had finished.

Scientists also saw an increase in birds gathering in the delta as the pulse inundated the channel, though the long-term return of migratory birds will depend on whether vegetation makes a significant comeback.

One of the most surprising outcomes of the pulse, though, was less ecological than it was social. Last spring, residents of Mexican towns near the channel gathered at the river to celebrate its inspiring — if temporary — revitalization. “Most of the time we think about the birds and wildlife,” Zamora says, “but in this particular case, the benefits and the connection of the local communities with the river was very evident. There’s new hope.”

The pulse perhaps got the most attention for connecting to the sea, but Flessa says that was beside the point. The real purpose of the international agreement to release the pulse — contained in a document called Minute 319 — was to breathe life into the larger ecosystem and to gather data on how to most effectively use water in the future. Still, some of Flessa’s colleagues couldn’t help but put bets on whether the release would reach the sea “Though I didn’t put any money down, I didn’t think it would,” Flessa said. 

Long-term effects of the pulse will be studied in the months and years to come. A more comprehensive report is due in 2016 and a final evaluation in 2018. 

Tay Wiles is the online editor of High Country News. 

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