Fresh stands of cottonwood and willow trees rising in the Colorado River Delta are evidence of the lasting environmental benefits an eight-week “pulse flow” of water deliveries to the area more than two years ago, according to a newly released report by U.S. and Mexican scientists.

The study delivered to the International Boundary and Water Commission also showed an increase in the number and diversity of birds in the area following the unprecedented binational effort.

“One of the concerns that people had about the pulse flow was that it was just going to be an ephemeral, onetime thing that wouldn’t have any lasting effects,” said Karl Flessa, a University of Arizona professor and co-chief scientist of a binational team that monitored the pulse flow. “We’ve shown that after two growing seasons that there are real long-lasting results.”

The study, known as the “Colorado River Limitrophe and Delta Environmental Flows Monitoring Interim Report” looked at the effects of releasing 105,000 acre-feet of water into the delta from March 23 to May 18, 2014. The onetime delivery of water from Lake Mead was aimed at reviving some of the delta’s last remaining wetlands, which have grown increasingly dry as a result of growing demands on the river upstream.


Hector Zamora, a University of Arizona doctoral candidate and member of a monitoring team, posed last August by willow trees that have sprung up at a restoration site in the Colorado River Delta. (Karl Flessa/University of Arizona )

The report measured the effects through December 2015, was presented in May, but not available to the public until last week. A final report is due in June 2018.

The pulse flow was part of a wide-ranging five-year agreement known as Minute 319 that was reached by the United States and Mexico in 2012 .The aim was to mimic flood conditions in the delta, a threatened, biologically rich area at the river’s mouth . In addition to the pulse flow, a base flow of 53,000 acre-feet is being delivered over a five-year period.


Minute 319 expires in 2017. The U.S. Boundary and Water Commission, IBWC, and its Mexican counterpart, known as CILA, have been negotiating a follow-up.

Osvel Hinojosa, a wildlife biologist with the Mexican environmental group Pronatura Noroeste, said the study is helping inform the environmental aspect of any future agreement.

A woman plants a willow tree in the Laguna Grande restoration area in the Colorado River delta in March 2014. (Charlie Neuman UT San Diego/Zuma Press )