A Pulse of Life for the Delta
The Conservancy is excited to be part of an historic event as the U.S. and Mexico release water into the Colorado River Delta.
"Willows that germinated during the pulse flow were already well over our heads just six months later!"
By Eloise Kendy, Freshwater Scientist for The Nature Conservancy
Monitoring a Rebirth
My friend and colleague Dale Turner and I were excited to return to the path of the historic Colorado River pulse flow, a release of water designed to rejuvenate the dry delta. We had taken photos before and during the water release in spring 2014, and now we were returning six months later, anxious to see the changes the “pulse of life” had brought forth.
The release of river water back into its parched delta was a shining star of cooperation for the environment. Discover Magazine and the US Department of Interior are among those hailing the event as a top achievement of 2014.
By all accounts, the pulse flow’s most important outcome is that it actually happened. For so long, the forces against it seemed overwhelming.
With western water such a scarce commodity, and so many entities drawing water from the Colorado River, a binational agreement seemed unlikely to gain any traction. But against these odds, an agreement was forged.
More than 105,000 acre-feet of water (equal to 34 billion gallons) was released in one large pulse flow between March 23 and May 18, 2014. That’s less than one percent of what would naturally flow into the delta without all the upstream diversions. Since it came as such a big surge over such a short time, the river channel and floodplain were inundated. Cottonwood and willow seeds filled the air. To everyone’s surprise and delight, the pulse flow temporarily connected the river with the Gulf of California.
Now Dale and I were back to document the impacts it had on the river environment. What would we see?
The Delta Blooms
In terms of restoration, everything we expected to happen happened. We expected native willows and cottonwoods to germinate wherever the pulse flow inundated bare soil, and that happened. However, there wasn’t much bare soil. A natural flood would have scoured out vegetation, leaving fresh, new soil surfaces behind. We knew the pulse flow was too small to do that critical scouring work. As a result, native plants germinated primarily on surfaces that had been mechanically cleared, mostly in restoration areas along the river’s path.
We also expected the new seedlings to survive where they received supplemental water through the summer. That happened too. The supplemental water, officially called “base flow,” is water that’s purchased from willing Mexican farmers by the Colorado Delta Water Trust, which The Nature Conservancy and other non-governmental organizations established for this purpose.This water is then delivered to restoration sites instead of to farms.
During this trip, we discovered that new seedlings did not survive where they didn’t get water delivered hrough the summer. We expected that, but secretly hoped we would be wrong.
In one area, willows that germinated during the pulse flow were already well over our heads just six months later! This confirmed our theory that a pulse flow is only one of several critical ingredients—scouring, seeds, and sustained access to water—for establishing new streamside habitat.
Success Beyond Expectations
We also observed how the pulse flow benefitted existing vegetation throughout the surrounding area, well beyond designated restoration sites. There was a 43% increase in green vegetation in places the pulse flow inundated, and a 23% increase in the broader riparian area.
Binational negotiations for another agreement will begin soon. Once again, the Conservancy and our partners will play a prominent role in those talks. Our goal is more pulse flows to restore more river reaches until, over time, we fulfill our longterm vision of well-connected, self-sustaining streamside habitat that supports diverse local and migratory birds in the Delta. To that end, the binational science team, which I co-manage, will continue to monitor hydrology, vegetation, and wildlife through 2017 to inform future pulse flow designs.
As a scientist who cares deeply about the environment, it’s hard to put into words what it means to be part of this successful and historic work.