From The Arizona Daily Star (Tony Davis):
…a second round of releases is headed to the delta that won’t be nearly as dramatic [as the Minute 319 pulse flow]. But these flows will restore more riverfront with cottonwoods and willows than the last time and their impacts will likely last longer.
The new U.S.-Mexico Colorado River agreement, announced last week, sets aside 210,000 acre-feet of river water for environmental restoration in the delta over nine years, starting next year. This 2017 agreement also calls on the two countries to share shortages on the river in equal proportions in times of drought.
The earlier, 2012 agreement under which the huge pulse flow was unleashed also enabled the more gradual release of another 53,000 acre-feet over four years that will end Dec. 31, 2017.
The first round of flows has restored about 1,100 acres of cottonwood, willow and mesquite habitat, said Osvel Hinojosa, water and wetlands program director for Pro Natura Noroeste and a co-chair of an environmental working group that developed restoration ideas for the new agreement. Pro Natura is headquartered in Ensenada, Baja California.
In that time, more than 230,000 native cottonwoods and willows were planted along the river, said a coalition of six U.S. and Mexican conservation groups calling itself Raise the River. The groups raised more than $10 million for restoration work and to buy water rights for those releases.
This time, the goal is to restore about 4,300 acres over the next nine years, the new agreement says.
Now, “We will see a resurgence of the Colorado in its delta, the ribbon of green that is re-emerging in the Sonoran Desert,” said Jennifer Pitt of the National Audubon Society at last week’s signing ceremony in Santa Fe, New Mexico. “It offers relief to every living being that seeks rest in the cool shade of a cottonwood, renewal in the bounty of life that flows from the waters of the Colorado River. We are finding new ways to share the water, among our communities, but also with hundreds of thousands of egrets, herons, flycatchers, rails and other birds that need it to survive.”
Although smaller pulse flows may be released later, the immediate plan is to focus on lesser, steadier amounts of base flows, Hinojosa said. Pulse flows release lots of water over short periods from a single point such as the dam. Base flows deliver lesser amounts, often over longer periods to specific restoration sites.
“At this point, the best way to proceed with restoration is base flows. That’s the best use of the water,” said Karl Flessa, a University of Arizona geosciences professor who oversaw the scientific monitoring of the 2014 pulse-flow impacts and hopes to be involved in similar work this time.
A lot of the 2014 pulse flow infiltrated into deep groundwater and was not available to nourish cottonwoods and other trees, he said.
“By applying base flows to restoration sites, you make sure water gets to the right place at the right time,” Flessa said.
Hinojosa said he considers base and pulse flows equally valuable, and may want to use smaller pulse flows for social purposes — allowing people living nearby to enjoy water in the river and reconnect with nature.