Chasing the Historic “Pulse Flow” Through the Colorado River Delta

Water moves over the sand on the leading edge of the Colorado River Delta pulse flow. (Photograph by J Pitt, EDF)

For one week now, the Colorado River has been flowing into its delta.  It’s the first ever deliberate release of water here to benefit the environment.

That the river is flowing again in its delta is somewhat astounding, all the more remarkable because it’s happening as the result of cooperation between the United States and Mexico under a new collaborative agreement on river and water management.

These releases – lasting eight weeks – are being made from Morelos Dam, about 100 miles (160 kilometers) upstream from the river’s end at the Upper Gulf of California (Sea of Cortez).  About 75 of those river miles (120 kilometers) are typically wet, either from a high groundwater table or the tides that make their way upstream.  But a reach of about 25 miles of the channel have been dry for decades, hot sand baking in the desert sun.

For the Colorado River to flow all the way to the Upper Gulf it needs to cross that sandy reach, and on March 29, 2014 it had made it down about 20 of those 25 miles, and about 40% of the total flow volume had been released.

I spent the afternoon chasing the water, as I have for much of the last week.

To get to the river we drive down farm roads to the levee, where we leave our vehicles and walk across farmland towards the channel.

After years of little or no flow in the dry reach, the old floodplain has been taken over by salt cedar, an invasive shrub with deep roots that can survive in salty soils on little water.

I walked upstream and found the water creeping down.  Water watchers are out every day, tracking the river’s progress as it travels downstream.

While the leading edge can look like a trickle, all you have to do is walk a few feet upstream to find the flow.  We anticipated that a lot of water would infiltrate the sand, but will have to wait for the scientists who are monitoring the flow to tell us how much surface flow is lost along the way.  (It’s not really “lost” though; once it soaks into the sand it becomes part of the groundwater.)

I think it will take another day or two for the river to complete its traverse of the dry bed.  When it hits standing water in the channel (evidence of a high water table), it will move faster, and less of the flow will be lost.  Once there it flows to the sea.

Run river run!

Wildlife

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Jennifer Pitt is the Colorado River Project Director for Environmental Defense Fund. She works with Colorado River water users throughout the Colorado River basin—including seven states in the United States and two in Mexico—to develop practical programs to restore river habitats and to dedicate water to environmental resources. She has worked as a park ranger and a Congressional aide, and has a Masters degree in Environmental Studies from Yale University.