Now in its 14th day, the historic pulse flow coursing through the Colorado River Delta toward the sea is under the careful watch of dozens of scientists who fan out across the landscape to measure and track its vital signs – from flow rates and salinity levels to seed dispersal by native cottonwoods and willows.
The goal is to learn as much as possible from this unique experiment in large-scale ecosystem restoration so that future pulse flows – designed to mimic the spring flood that naturally occurred before large dams and diversions were built – will deliver as many benefits to river health, habitat creation and local communities as possible.
“This is a once in a career kind of thing,” said Karl Flessa, professor of geosciences at the University of Arizona in Tucson and Co-Chief Scientist of the monitoring team for Minute 319, the binational agreement signed in late 2012 that established the terms of the pulse flow.
“Scientists all around the world are watching.”
One of the big dramas of the past week was whether the river’s flow would make it through the third of seven designated reaches of the river from Morelos Dam at the US-Mexico border down to the Sea of Cortez (Gulf of California).
Reach 3 is a wide, sandy stretch 21 miles (33.8 kilometers) long that’s partially underlain by a so-called groundwater hole – an area where heavy pumping has depleted underground water supplies and caused the water table to drop.
Surface water crossing this reach moves very slowly and is prone to high rates of infiltration.
While that’s good for recharging the groundwater supply, it’s bad for the pulse experiment because the main objective is to get as much flow as possible downstream to important restoration sites like Laguna Grande, where tens of thousands of native trees have been planted over the last several years.
The pulse flow is crucial to help the trees germinate and grow, as well as to encourage the natural regeneration of other sites along the river’s channel.
For Jorge Ramírez-Hernández, a team leader for hydrology monitoring and a professor at the Universidad Autónoma de Baja California, the pulse flow has brought long days and lots of worry.
In addition to water lost to infiltration in Reach 3, Ramírez knew that water was spreading into meanders and lagoons. While these river features often create good habitat, in this case they too steal water away from the critical mission of getting the river’s flow downstream.
Ramírez oversees two teams of students who monitor the Colorado’s flow at ten sites every day. They use a method called Acoustic Doppler Current Profiler (ADCP), which applies principals of sound propagation through water to measure flow velocity. When combined with the channel’s cross sectional area, it provides an estimate of the river’s discharge.
One day this past week, Edgar Carrero patiently moved back and forth across a 70-meter wide section of the river channel, taking and reporting measurements. Each monitoring team visits five sites, and typically works 16-hour days.
Carrero whistles as he slowly crosses the river. He’ll go back and forth 5-7 times to get the necessary readings.
On Wednesday this past week, when the advancing Colorado River met up with the higher water table of Reach 4, delta scientists breathed a sigh of relief.
“It was very exciting to see the leading edge get connected to Reach 4,” said Osvel Hinojosa Huerta, a wetlands ecologist and bird specialist with the Mexican conservation organization Pronatura Noroeste. Hinojosa has been working in the delta since 1998.
The swallows and cinnamon teals were not here this morning, Hinojosa said, standing near the location where the flowing river met the channel filled with groundwater. “They came after the water arrived.”
“We’ll be tracking birds very carefully.,” Hinojosa added. “They are good indicators of system health.”
The pulse flow was carefully timed to maximize the regeneration of native cottonwoods and willows, which disperse seeds in March and April. The seeds require moist soil to germinate, and those that fall on the flowing river’s surface will get dispersed downstream, where they can create new habitat for birds and wildlife.
In addition to studying three research plots at Laguna Grande, Karen Schlatter, a project manager with the Tucson-based Sonoran Institute and a graduate student at the University of Colorado in Boulder, helps conduct vegetation surveys at key sites in the river corridor.
To be able to work with a managed flow and study the vegetation responses “is pretty unique,” Schlatter said.
While a tremendous amount of information will be gathered from the pulse flow over the coming weeks, months and years, it is just the beginning of a long process of learning and adaptation with an aim of using the water available for delta restoration in the most efficient and beneficial way possible.
“This is a first step,” Flessa said. “A really important first step.”
Sandra Postel is director of the Global Water Policy Project, Freshwater Fellow of the National Geographic Society, and author of several books and numerous articles on global water issues. She is co-creator of Change the Course, the national freshwater conservation and restoration campaign being piloted in the Colorado River Basin.
If you’re not yet part of Change the Course, please join us. Check out our website or text “River” to 77177.
Special thanks to Silk and Coca-Cola, Charter Sponsors for Change the Course. Additional funding is generously provided by the Walton Family Foundation.