Changing Planet

Will the Colorado River Delta Pulse Flow Make it to the Sea?

The mouth of the Colorado River in the Gulf of California, where an historic “pulse flow” from upstream may soon arrive. (Photograph by J. Pitt, EDF)

One of the big unknowns of the pulse flow of water currently working its way down the channel of the Colorado River in its delta is whether that water will reach the sea.  The mouth of the Colorado River drained historically into the Upper Gulf of California (Sea of Cortez), a unique body of water that Jacques Cousteau called “the world’s aquarium.”  But with dams and diversions of Colorado River water serving a population of more than 35 million in the United States and Mexico, the Colorado River hasn’t reached its destination regularly since before 1960.

The pulse flow started on March 23, and will continue through May 18.  The flow rate varies over time, by design meant to inundate the channel and later to recede slowly and stimulate germination of the seeds that will grow into native cottonwood and willow trees.  In order to do this work the pulse flow waters must travel some 25 miles (40 kilometers) of sand that typically exist in the midst of the river’s 100-mile (160-kilometer) run in its delta.

We have been watching this progress for days, cheering its advance.  Run river run!

Colorado River pulse flow map

Progress has been slow but steady.

On the first day of the release we found cool, clear water advancing down the channel some 17 river miles (27 kilometers) below Morelos Dam.  The “front” moved quickly where the channel is typically wetted – even filled with standing water – due to a high groundwater table.  Since then, it has been crossing the sand, and significant volumes of water soak into the ground, recharging a depleted groundwater aquifer.

The map shows its progress, slow because of its need to saturate the sand as it goes, because of the low gradient in the flat delta, and because of the considerable presence of scrub brush (mostly non-native salt cedar) growing in the channel.

The pulse flow’s behavior has been hard to predict.  The river hasn’t flowed here in years, and moreover, no federal agency in the United States or Mexico had viewed the delta as its responsibility, so no agency had studied the delta in recent decades.

But now the United States and Mexico, in addition to implementing the pulse flow, are funding an extensive monitoring program, gathering information on how the water moves, how the channel changes, how the trees grow, and what the wildlife does as a result of the pulse flow.  Dozens of U.S. and Mexican scientists are spending their days collecting data that will be crucial to fleshing out our understanding of the pulse flow.  They are a hardy crew!

I’m grateful for their efforts as they brave hot sun and dense scrub to take samples and measurements that will tell the pulse flow story and help us improve how we design any future pulse flows (we will also need a new U.S.-Mexico agreement for that).

Colorado River channel
The pulse flow (far left) follows the lower Colorado River channel as the groundwater rises (right) on Wednesday. (Photograph by J. Pitt, EDF)

I have been visiting the front of the pulse flow nearly every day, and yesterday I had the extreme good fortune to see the front finish its journey down the sand.  The leading edge of the water finally arrived at the middle reach of the delta where groundwater is typically found in the channel.

Looking upstream, we watched the pulse flow creep forward.  Looking downstream, we watched the groundwater creep up the channel.  And eventually they met, marking the end of the pulse flow’s slow advance over the sand.

surface water meets groundwater in Colorado River
The water at left is rising groundwater and the water on the right is the leading edge of the pulse flow. (Photograph by J. Pitt, EDF)

Now that the dry reach has been saturated, we expect water to move more speedily.  The leading edge of the pulse flow will now travel the middle and lower reaches of the delta, reaches that are typically wet due to high groundwater and drainage from nearby agricultural fields.  Infiltration will not be nearly as great, and the water should run rather than creep.  The pulse flow still has miles to go, but these miles should be easier to travel.

Will the pulse flow reconnect the Colorado River to the sea?  We still don’t know.  We don’t even know that we’ll be able to see it when it does.  But scientists will be out there taking conductivity measurements, and will tell us if, and when, water at the river’s mouth becomes less salty as freshwater arrives.

Flow river flow!

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.
  • Maurice (Moe) Mareschal

    More water, more agriculture and people???? With peopolution rising as more humans flow to California/AZ, where will the water come from? … I know: Pessimism! But look at the history of Easter Island and its settlement…

  • Jesse

    I lived in Arizona for a while. After a while my conscience was really bothered by the way of life out there. Not a natural place for so many people. Got tired of the lawns, sprawling golf courses, water parks & fountains. An increasing amount of people want to live in places with lots of sun. But they still feel entitled to unlimited water no matter where it comes from. That’s gotta stop.

  • John Gottes

    If I may offer a small correction:
    The picture at the top of the article, labeled
    “The mouth of the Colorado River in the Gulf of California, where an historic “pulse flow” from upstream may soon arrive”
    is not a picture of the mouth of the Colorado River.
    The picture actually shows the mouth of the Santa Clara Slough, a few miles to the east.
    Picture looks good, but is not what it claims to be.

  • roberto alvarez

    I live on the are maurice , no one can swim the dam, this area has been protected from inmigrants, the water will flow to south,not to north,
    the best thing is that campo mosqueda will nor recive this flow
    as the was willing to charge extra to the visitors just foe the new good water, viejo tranza

  • Richard Roati

    We have only begun learning how to conserve – how to use our roof water, our street water, our laundry water, our bath water. With these efforts, the dry lands can become wet again. Now the Colorado Delta is once again moving towards the sea. May you run to meet the sea. Let the dry lands return to life.

  • Enviro Equipment, Inc.

    Other than stimulation of the native cottonwood and willow trees see seedlings, what other environmental benefits are there to flooding the Colorado River Delta?

  • John Goetten

    The 3 north bound Mallards I saw yesterday will be helped by more wet land in the Delta. The projected flow location of the “pulse” bypasses Rio Hardy. The past floods have not. Hopefully, we will all get some flow. Keep up the good reporting.

  • Jennifer MacLeod

    What a fascinating and fantastic story! Congratulations to all of you who worked so hard to make this happen. Well done! Flow, river, flow!

  • John Goetten

    Please date photos. The photo of the pulse/ground water join shows survey instrument legs setup and a dozer channel. Has a pilot channel been dozed for a great length and will the progress be update? How about some GPS locations so we can cross reference the flow progress with Google Earth photos. Thanks for the great reports.

  • John Gottes

    Sir John:
    From the pics I’ve seen, the dozer cut in the last photo is unique. Here is a YouTube video of the water advancing:
    I’m guessing the tripod legs you see in the photo are a photographer’s tripod – survey tripods are usually a bit more sturdy.
    Finally, I’d like to visit the mud flats on the lower delta, a bit south of the Rio Hardy down near the shrimp farm – do you know if you can drive on the flats?

  • Gerardo

    This effort is an important example for other natioms, It is a little step on the nature conservation.

  • John Goetten

    I have been told that it is possible to drive from below Yurimuri to El Doctor across the mud flats and I planned to try last weekend, but I did not have my Prowler with me. Google Earth looked a little sketchy to me. Photos are from a year ago of the delta.

  • John Goetten

    Jennifer, How about an update on the flow. It has been over a week without a position report.

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