In the spring of 2014, a rare moment happened on the lowest stretches of the Colorado River. Instead of its last few drops being diverted at a dam near the U.S.-Mexico border, it flowed through its banks.
鈥淭here was a remarkable amount of excitement and energy in the air,鈥� says James Leenhouts, a U.S. Geological Survey hydrologist who runs the agency鈥檚 Arizona Water Science Center and was present for the moment. 鈥淥ne of the most remarkable impacts of the flow was the human impact.鈥�
In communities where the river hadn鈥檛 flowed for nearly two decades, impromptu festivals broke out, children waded into the water and mariachi bands set up to entertain the crowds. As the water settled into the valley it was clear the 鈥渆xperimental pulse flow鈥� made a profound cultural imprint on the region the Colorado River once regularly flooded.
A group of scientists, including those from the U.S. Geological Survey, are also gaining insight into how the flow was felt by plants, animals and the overall delta ecosystem.
Using a mix of groundwater monitoring and satellite imagery, scientists say even the pulse鈥檚 modest flow of water 鈥� approximately one-twentieth the amount that spilled into the delta before humans built the river鈥檚 massive upstream dams 鈥� recharged aquifers, greened plant life and spurred the return of bird species.
Years before the flow, Mexico and the United States agreed to the experiment, and to the idea that the water was not just for human use, but can and should be used to revive ecosystems. The agreement -- an update to a 1944 treaty between the two countries -- gave Mexico the ability to store more water in American reservoirs and, just once, flood the final miles of the dry river bed to see what happened.
From above you can use the naked eye to see the water鈥檚 effect. Before and after photos show plant life greening not just in the river鈥檚 bed where water actually flowed, but beyond the banks, which Leenhouts says is a sign of recharged groundwater.
鈥淚n the two years following the flow it was possible to measure increased green up,鈥� using satellite images, he says.
During that same period both the number of and varied species of birds increased, he says, a side effect of the revived vegetation.
Even though the pulse flow only lasted a few months in 2014, its effects lasted for years. The greenness of vegetation wasn鈥檛 as vibrant the following year, but it was still greener compared to 2013. That indicates the single sustained flow provided enough water to keep plants alive for at least a year.
Because the amount of water was significantly lower than a natural flood, the water鈥檚 power was diminished. In an unencumbered flood, the water鈥檚 power would rip out non-native plants, move sediment and reshape its banks. During the pulse the water was more effective in areas where scientists and volunteers had cleared out invasive plants or moved sediment piles by hand.
鈥淲hat we were able to ask ourselves is, 鈥榳hat鈥檚 the best [way] to do this in the future?鈥欌�� Leenhouts says.
Scientists鈥� chance to study and test the effect of simulated floods isn鈥檛 over. A new update to the 1944 treaty signed this year allows for more pulse flows when Mexico stores surplus water.
This story is part of a project covering the Colorado River, produced by KUNC and supported through a Walton Family Foundation grant. KUNC is solely responsible for
