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New ‘Pulse Flow’ Raises the Colorado River in Mexico

July 19, 2021
From May to October, a surge of water is replenishing the Colorado River Delta

Seven years ago, the Colorado River Delta found its pulse when 105,000 acre-feet of water was released into Mexico from the Morelos Dam, filling dry channels and reviving wetland habitat. For the first time in decades, the Colorado flowed from source to sea.

The 2014 "pulse flow" recharged a portion of the West’s most important river that has been dying of thirst since the middle of the last century. It also reignited the memory and imagination of Mexican residents of the Delta, who celebrated the return of water and began to understand the river’s potential to support nature and people in the region.

For scientists, conservationists and governments, the pulse flow was a learning event. We learned that communities were enthusiastic about restoring the Delta and ready to seize the opportunity created by conservation projects in areas once dry and desolate.

A flowing river benefits the environment and local communities. The Vado Carranza site has been popular with kids of all ages to cool off on hot summer days.

We also learned it was possible to provide greater environmental benefit to the river with smaller flows over multiple years. To build on the 2014 pulse flow’s success, the U.S. and Mexican governments in 2017 reached an agreement – called Minute 323 – that provides at least 210,000 acre-feet of water over nine years for ongoing riparian restoration and recreation in the Delta.

Fast forward to this summer – and the Colorado River is again flowing in the region.

The first water from the 2021 "pulse flow" is delivered at the Chausse restoration site in the Colorado River Delta.

For 126 days, from May to October, more than 35,000 acre-feet of water – about 11 billion gallons – is being released into the Delta, supporting local economies and improving riparian and wetland habitat for wildlife.

The timing and rate of flow for this year’s release were designed by a team of scientists to maximize environmental and recreational benefits.

The current flow coincides with seed dispersal from cottonwood trees – mimicking how floods and seeds have coordinated for millennia – and to maximize recreation during the hottest part of the summer.

While only one-third as big as the 2014 pulse flow – and a fraction of the river’s historic flows – even this smaller amount of water is making a big difference in the health of the delta region.

Throughout the Colorado River Delta, the coordinated release of water is bringing life back to this region.

Instead of releasing the water directly into the river at the border, water managers have bypassed the Morelos Dam via canals and released the water about 45 miles downstream. By doing this, more water is delivered to restoration and recreation areas and avoids being absorbed into the driest parts of the river channel.

The flows are delivered to existing restoration sites where they flush salts from soils, replenish local groundwater and provide seasonal habitat for migratory and resident waterfowl. Diverse wildlife – from beavers to panthers – are also returning to the river.

Because the flows are delivered to the central Delta through canals, they are also benefitting local farmers. The extra water in the canals helps water reach farms further down the Delta and reduce salinity, which improves agricultural productivity.

The release of water was carefully planned at strategic points near restoration sites to maximize impact.

This year’s flow is proving the value of collaboration that made the 2017 binational water-sharing agreement possible. The deal included a unique three-party arrangement among the U.S. government, the Mexican government and Raise the River, a coalition of six nonprofits committed to conservation in the Delta. While this flow is delivered by the U.S. to meet its obligations under the agreement, our partner organizations in Raise the River are providing additional flow to all of the restoration sites and to the lower river channel every year.

Coming in the midst of the worst drought year on record, as the West is experiencing shortages in available water, this year’s Delta flow is a testament to the strength of Minute 323 and commitment of its partners to community and environment.

By mid-June, the released water reached the sea in the estuary region of the Colorado River Delta.

The agreement has become a global model for binational river management, showing how we can invest in water projects that conserve and share water between countries and dedicate environmental water at the same time.

There is much more work to do for all of us who care about the Delta’s future.

Of all the ecosystems impacted by the harnessing of the Colorado in the 20th century, the Delta suffered most. The construction of the Hoover Dam in the 1930s, and then the Glen Canyon Dam from 1956 to 1966, sapped the Delta of its fresh water and sparked its decline.

Riparian forests of cottonwoods, willows and mesquite, as well as marsh and estuarine wetlands, that once thrived across about 2 million acres now cover just a small fraction of that area.

The 2021 "pulse flow" aids restoration of riparian habitat at the Chausse site, where native cottonwoods and willows grow along the riverbank and native grasses populate revived marshes.

But based on a decade of testing and refining successful restoration practices, the potential of reconnecting the river to the sea is now in reach.

We see that in the success of this year’s flow.

As of late June, the river is reconnecting with the sea. During high tides, flows in the river channel are meeting the Delta estuary in the Sea of Cortez, mixing fresh water with salt water to sustain estuarine marshes.

As summer builds toward fall, we’re hopeful that this year’s flows will continue to reach the sea, reconnecting the river once again as it did in 2014 – and hopefully as it will do again in the future.

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