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Colorado River

Explaining the Delta Pulse Flow

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.


The work of Nature Conservancy scientist Eloise Kendy is going to be part of an historic event that will grab the world’s attention. She’s a hydrologist and member of the team that designed the Delta pulse flow—a water release—a key element of the Colorado River bi-national agreement to restore the Delta region. This 100-mile stretch of the river has rarely flowed to the Gulf of California since 1960. The binational agreement, signed by the US and Mexico, also defines how the two countries will share and store water in times of surplus and shortages.

When she’s not working on this pilot project or developing freshwater solutions, Eloise enjoys hiking, mountain biking and whitewater rafting in her home state of Montana. sat down with Eloise to learn more about her experience.
"This project shows how stakeholders with diverse interests can come together to manage the river for people and nature in the face of drought."

- Conservancy Hydrologist Eloise Kendy

For someone who's never heard of a pulse flow, what is it?

Eloise Kendy:

Think of it as a surge of water. It’s what happens when there’s a big rainfall or the snow melts into a river. The flow increases for a few days or weeks, and then it goes back to normal. Rather than weather, this environmental experiment will be a release of water from a reservoir. It is designed to mimic the kind of natural pulse flows that help keep rivers healthy by spreading native plant seeds and creating conditions for those seedlings to grow and thrive.

Who was on the pulse flow design team?

Eloise Kendy:

The team consisted of a wide array of governmental, non-governmental and academic scientists from the U.S. and Mexico who have decades of experience in river hydrology and ecology.

What went through your mind when you were invited to be part of this team?

Eloise Kendy:

I feel like this is the crown of my career. I was thrilled to have the opportunity to contribute to such an historic event! After studying rivers for more than 30 years and a decade of promoting, leading, and facilitating teams like this, I knew I had a lot to offer and I was happy to help.

What was the team's approach?

Eloise Kendy:

The bi-national agreement allocates less than 1% of the river’s average annual flow to this event. We are trying to engineer a spring flood, even though the amount of water is very small compared to the natural spring floods of before the dams, when 70% of the annual flow arrived in three months. It was our job to recommend the timing, duration, peak flow rate, and how fast the flow rises and falls in order to improve river health, revive wildlife habitat and help native trees flourish.

There was a lot of back and forth in the four-month process due to legal, political and physical hurdles. The science team would come up with a plan and the water managers from both sides of the border would send it back for revision. We were very excited when the plan was finalized!

What other challenges did you encounter?

Eloise Kendy:

Groundwater, vegetation, climate and land conditions are quite different from the last time water regularly flowed in this region, around 50 years ago. Despite the existing scientific knowledge, it is very difficult to predict the environmental effects of the pulse flow. That’s why it’s so important that we monitor and learn from this experience so we can answer those questions in the future.

After several months designing the pulse flow, what do you expect it to look like?

Eloise Kendy:

Imagine the water rising rapidly for five days in the riverbed until it spills over its banks. In some places, there is already standing water. But for 25 miles, the riverbed is dry. Perhaps the most dramatic scene will be where the pulse transforms this reach of sandy, barren desert into a flowing river. After three days of high flows, the water will begin to recede, rapidly at first and then more slowly for several weeks. The farther downstream you go, the lower the peak will be and the longer the overall flow will last.

What kind of impact could this water release have on the Delta region? What about the overall health of the Colorado River?

Eloise Kendy:

The impact we’re aiming for is healthy, self-sustaining cottonwood and willow trees in the Delta, enjoyed by flocks of local and migratory birds. We also hope to flush the estuary in the lower Delta with much-needed freshwater. If the pulse flow is successful, we hope to be able to do this kind of release more regularly in the future, which could also generate rural economic activities and job opportunities for local people including river restoration, tourism and commercial fisheries.

On a larger scale, this project shows how stakeholders with diverse interests can come together to manage the river for people and nature in the face of drought. If we can do it across international borders, then surely we can do it in the rest of the Colorado River Basin and other places in the world!

You mentioned earlier that a critical part of this project is monitoring. Tell us more.

Eloise Kendy:

More than 50 Mexican and US scientists and engineers are going to measure the pulse flow and the changes it brings to groundwater, plants, birds, fish, and wildlife over the next five years. We’ll be measuring everything from river level and water quality changes to plant and animal responses. In addition to troubleshooting, I’ll be measuring water levels and water quality in observation wells with students from the Universidad Autónoma de Baja California. The information we gather will be used to understand how best to restore the Delta going forward. We hope this groundbreaking experiment becomes a model for sustainability that can be used anywhere in the world.

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