Mexico now takes a cut in its annual allocation if Lake Mead drops below certain thresholds. One, the agreement brought Mexico into the shortage agreements that were worked out in 2007 between Arizona, California, and Nevada. Parties on both sides called Minute 319 “historic,” for several reasons.
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Every few years, the United States and Mexican governments update a 1944 treaty over shared rivers. The water for the pulse flow came from an agreement called Minute 319. “To have a river suddenly come through the community was something special and people want to see more of that.” More Delta Water in Next Agreement? “People in this area have for a long time gone without knowing that they have a river nearby,” Schlatter told Circle of Blue.
Karen Schlatter, an ecologist at the Sonoran Institute and a co-manager of the monitoring team, recalls families in the Mexicali Valley kayaking and swimming in the river, some for the first time. Photo courtesy of Wikimedia CommonsĮven though it focused on science, the report notes that the pulse flow experiment had deep social importance too. Water channels form fractal patterns in the sands of the delta. “It’s not enough anymore to dump water into the riverbed,” Flessa said. Instead of sending water through porous stretches of the river channel they redirected the flow through irrigation canals, to avoid seepage. On the bare ground they seeded native willow and cottonwood. They connected meanders to the main channel by excavating and grading the soil. They pulled out invasive plants such as tamarisk. Because a limited amount of water is available, large-scale restoration projects like this need to be managed, not left to nature, he said.įor the pulse flow to reach the targeted restoration areas, project managers had to be directors. That fact leads Flessa to another conclusion. The pulse was a faucet drip, not a firehose. At its peak, the river in April 2014 was less than three percent of the median flood discharge before 1935, when Hoover Dam walled off Boulder Canyon hundreds of miles upstream. The pulse flow may have mimicked a pre-dam spring flood, but it was a faint resemblance. “The key lesson here is that even though it was a short-term event, it is actually having lasting effects on vegetation and birds,” Karl Flessa, a University of Arizona professor and chief scientist monitoring the pulse flow, told Circle of Blue. The findings will guide the long-term restoration of an area that is an internationally significant bird habitat and home to several endangered species. The study, the second of three scientific reports that will be released, assessed the condition of the delta after two growing seasons, through December 2015. Researchers are hopeful that the success of the pulse flow experiment will prompt negotiators to allocate more water to the delta. A new agreement is now being discussed, and another round of environmental flows is likely to be included. The source of the pulse flow water is an agreement between the governments of the United States and Mexico. There are social and political benefits, too. Water reached the Gulf of California, some 77 miles from Morelos Dam, for the first time since 1997. The fraction that traversed the entire course of the river channel completed a symbolic journey. Nearly 95 percent of the water soaked into the ground and recharged the aquifer. The vegetation helped boost the abundance of 19 key bird species by 49 percent. Birds - Gila woodpecker, brown-headed cowbird, ash-throated flycatcher, yellow-breasted chat and others - flocked to the new habitat.
The pulse flow flushed salts from the soil, which aided the growth of native trees. Researchers found that the change in the delta was rapid.Ĭottonwoods and willows that germinated during the pulse flow now shade the scientists who are studying them. A scientific assessment of the pulse flow was made public on October 19 by an international team of researchers who are studying the delta ecosystem’s response to the surge of water. Scientists can now back the sentiment with data. River communities in Mexico, some with teenagers who had never seen water between the banks, called it a blessing. For the next eight weeks, water pitched into the dry bed of the Colorado River, wetting its delta like the spring floods that coursed through braided channels before the river was dammed.Īuthorities called it a pulse flow. On March 23, 2014, the gates were opened wide at Morelos Dam on the U.S.-Mexico border near Yuma, Arizona. Photo courtesy of Francisco Zamora/Sonoran Institute The short-term flush of water, which took place over eight weeks, had lasting ecological and social effects. Water from the Colorado River flows into the Gulf of California in this photo taken on May 23, 2014.
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