‘Pulse flow’ boosts Colorado River habitat


In the arid Colorado River Delta of the U.S.-Mexico border region, even a little water works wonders in restoring a critical binational ecosystem. For the University of Arizona’s Karl Flessa that’s one of the primary lessons from a recently issued report on a project that delivered a water infusion, called a pulse flow, that inundated 4,000 acres (1,600 hectares) along the lower Colorado River’s main channel in 2014.

Though relatively small, the water releases at three locations on the lower Colorado managed to restore the river’s flow to the Gulf of California for the first time since 1997. Historically, the Colorado’s waters reached the Gulf of California; but heavy use of its water, mainly in the United States for drinking and irrigation, has caused the river in all but a few of the past 50 years to peter out well short of the sea.

The project to conduct a pulse flow and subsequent, complementary base-flow releases were authorized in Minute 319, a Colorado River water agreement that the United States and Mexico reached in 2012 through their binational International Boundary and Water Commission (IBWC). An interim report on the results, issued in October, was prepared by a transnational research group co-led by Flessa and Carlos de la Parra of Mexico’s Colegio de la Frontera Norte (Colef), a Mexican institute that focuses on border issues. A final version of the report is expected in 2018.

Studies conducted after the pulse flow by the binationally funded group, called the Colorado River Delta Minute 319 Monitoring Program, reported positive environmental impacts from the release of 105,392 acre feet of water over eight weeks, from March 23 to May 18, 2014. These included the recharging of aquifers, germination of native cottonwood seeds, a greener landscape and an improved presence of bird species in a place experts consider a vital link in North America’s migratory flyway.

The pulse flow targeted the lower Colorado between the Morelos Dam, located on the U.S.-Mexican border, and the river’s historic, once-verdant delta on the upper Gulf of California. Writing in 1949 about a canoe trip through the delta two decades earlier, the late U.S. naturalist Aldo Leopold described a rich patchwork of wetland and forest with “awesome jungles” and “lovely groves.” Then, however, came decades of water-diversion projects built by the U.S. Bureau of Reclamation to supply drinking water in seven states and irrigation for millions of acres of farmland in California, Arizona, Colorado and Nevada. Mexico tapped the Colorado, too, steering water to the fast-growing industrial cities of Mexicali and Tijuana, as well as to farmland in the Mexicali valley. As a result, the Colorado’s flows rarely reached its historical mouth.

Conservationists hope that findings from the experimental release of water conducted under Minute 319 will build a case for allocating water regularly for so-called “environmental flows” to the long-parched delta. Designated a protected biosphere in Mexico and covered under of the international Convention on Wetlands, or Ramsar Convention, the Colorado River delta and the upper portion of the Gulf of California provide habitat for animals including shorebirds, fish, crustaceans and the endangered vaquita porpoise (Phocoena sinus). Experts say such releases could bring benefits upstream as well.

“As we say, these are ecosystem services that go far beyond [restoration of] the delta,” Flessa says. He notes, for instance, that healthier local habitat for waterfowl ultimately benefits activities such as duck hunting north of the border.

Intended to simulate a spring flood, the pulse flow has been supplemented by the release of another 52,696 acre-feet of Colorado River water that was set aside for smaller infusions, called “base flows,” later in 2014, in 2015, this year and possibly in 2017. In the months after the pulse flow, researchers saw a greater number of waterfowl—including a 49% increase in species of “conservation interest,” among them the gila woodpecker (Melanerpes uropygialis), brown-headed cowbird (Molothrus ater) and the ash-throated flycatcher (Myiarchus cinerascens).

Compared with most of the lower Colorado River’s floodplain, researchers detected a greater abundance of avian species in environmental restoration sites that had been prepared by nongovernmental participants in the project, among them Pronatura of Mexico and the Sonoran Institute of the United States.

“It was a good response,” says Osvel Hinojosa-Huerta, water and wetlands director for Pronatura, which like the Sonoran Institute has pushed for restoration of border-region ecosystems that have suffered from the damming and channeling of the Colorado River. “It was a little more than we expected.”

Gauging the density of cottonwood (Populus fremontii) and willow species (Salix gooddingii) in 2014 and 2015, researchers concluded that environmental flows likely contributed to the establishment of native riparian seedlings in at least two reaches of the study zone. They point out that the native species frequently do better than invasive tamarisk (Tamarix ramosissima), registering rapid growth in height and canopy and creating an improved avian habitat. Compared to 2013, the year before the pulse flow, the preliminary study calculated a 16% increase in “greenness” along riparian reaches in 2014, a change that lasted until 2015.

Jennifer Pitt, Colorado River specialist for the National Audubon Society, says it is essential to consider the possible benefits of preparatory work done before the pulse flow by Pronatura and partner organizations. The groups cleared out invasive species, replanted native vegetation and prepared the land for flooding.

While post-pulse-flow surveys showed a “significant uptick in the number of birds, both in species and populations,” Pitt cautions that it’s still not clear exactly how much of the avian increase was due simply to the water inundation or the more “durable” habitat changes brought about by the removal of invasive species such as salt cedar and the planting of native cottonwood—or both.

Gilbert Anaya, chief of the USIBWC’s environmental management division, agrees with Flessa that the land preparation was an important factor in maximizing the pulse flow’s effects. “You can’t have one without the other,” Anaya says.

The U.S. government, the Mexican government and environmental groups all took part in providing the Colorado River water for the pulse and base flows. Exceeding a fundraising goal of US$10 million, Mexican and U.S. environmental organizations purchased water rights from Mexican owners, according to Pitt.

Stephen Mumme, a professor of political science at Colorado State University, calls the purchase of water rights from Mexican owners a “creative” solution that skirted the thorny matter of allocating new water resources in a supply-strapped basin. Pulse-flow effects such as recharged aquifers also encourage discussion among Colorado River users about additional groundwater resources, says Mumme, a longtime analyst of U.S.-Mexican water policy.

The pulse-flow project was not without shortcomings. Flessa says it was determined that the amount of water employed for the flow wasn’t big enough to scour and bare the land surface for optimal seed germination, hence the importance of the pre-flow land preparations.

Secondly, the water flow didn’t mix long enough with Gulf of California water at the mouth of the Colorado River. Traditionally, shrimp and other aquatic species, including commercially harvested fish, thrived during the early stages of life when there was abundant mixing of fresh and salt waters. “Losing these nursery grounds has adverse effects on these species, including endangered species like totoaba,” Flessa affirms.

The U.S.-Mexican research team concluded that in order to enhance marine life in the upper Gulf of California, it would be necessary to provide more water for environmental flows. Also needed, they say, is the opening of a channel through a sandbar that currently restricts tidal flows in the lower reaches of the river.

Research on the pulse flow’s effects on the lower reaches of the Colorado is being carried out collaboratively with the Sonoran Institute, which pitched in with resources and people. The U.S.-Mexican research team acknowledges the need for more such work. “Additional research, including modeling and experimental flow deliveries, is needed to estimate the amount and timing of flows required for [marsh land] enhancement,” the binational research group concludes in its recently issued report.

Flessa and Hinojosa-Huerta say they are studying whether it would be more efficient from an ecosystems standpoint to conduct a greater number of releases with lesser amounts of water. In doing so, they’re pondering how to maximize processes ranging from aquifer recharge and soil-salinity management to seed germination and wildlife-habitat growth.

Negotiators from the U.S. and Mexico are now hashing out a successor to Minute 319, which was approved in 2012 as an amendment to the 1944 treaty governing U.S. and Mexican use of water from the Colorado River and the lower Rio Grande River. The amendment allows the two countries to share water surpluses and shortages, permits Mexico to store some of its allotted water in U.S. reservoirs and encourages Mexican water-infrastructure investment.

Most importantly from the perspective of ecologists, however, the measure permits water to be released on an experimental basis to reestablish flows of the Colorado River to the Gulf of California. Negotiators are talking about making these so-called environmental flows part of the successor agreement to Minute 319, which is set to expire on Dec. 31, 2017

“The agreement with Mexico is extraordinarily important to the states in the U.S. that use Colorado River water,” says Pitt, who participated in the talks that originally birthed Minute 319.

The 2012 accord permitted Mexico to store up to 1.5 million acre-feet of its Colorado River water allocation in the U.S. state of Nevada’s Lake Mead. A portion of that water was used for the pulse flow.

Tapped by an estimated 40 million people in increasingly water-strapped states of the U.S. and Mexico, the Colorado River faces a complex future of resource competition and political jockeying. However, participants in ongoing Colorado River Delta environmental restoration efforts say their common cause has brought together non-governmental organizations, government agencies and academics from both sides of the border.

“It’s really quite extraordinary to have that level of coordination across borders…Sometimes when government agencies get involved it becomes complicated, but we’ve shown it can be done,” Flessa reflects. “This may be one of the first cases where water moved across borders for environmental reasons.”

Hinojosa-Huerta, too, finds mutual benefits in the transnational cooperation. “On the one hand, it’s a challenge,” he muses. “It takes time and effort to coordinate, but it’s fundamental.”

Recommendations from the pulse flow research have been forwarded to the negotiators working out a successor to Minute 319, including a proposal to conduct what Hinojosa-Huerta terms periodic “mini pulse flows” strategically designed to maximize environmental benefits. Sally Spener, foreign affairs officer and spokeswoman for the USIBWC, says negotiating work groups with members from Mexico and the U.S. are busy hammering out a new Colorado River water agreement expected to be signed before Minute 319 expires later next year.

“We’re still working on it,” Spener says. “We would expect that agreement to have an environmental component that would include an environmental water component.”

With Donald Trump set to assume the U.S. presidency in January, some are questioning whether the direction of Colorado River water policy might shift as a result.

Mumme, for his part, does not forecast a major departure: “I don’t see a new administration coming in and bollixing it up.” He adds that changes in administrative personnel under Trump might delay but likely would not prevent a successor to Minute 319, given the numerous stakeholders vested in a new version of the agreement. “There are too many parties and predecessor agreements that go into it,” he says.

Cautioning that campaign rhetoric is apt to clash with policy realities and that “nobody can really say what is in a Trump administration,” De la Parra declines to venture an opinion. “I’m a kind of wait and see guy,” he says.

Mumme argues that while the pulse flow did not “restore ecology all the way down the river,” such flows and their inclusion in Minute 319 represent a “step forward” in protecting and improving the Colorado River and Delta ecosystems. Despite the challenges facing these efforts, Mexico and the United States have “high incentives” to continue collaborating, given their shared tourism, Pacific migratory flyway and other cross-border benefits, he says.

For Hinojosa-Huerta, continuing binational cooperation benefits both Mexico and the United States. “I have much faith in my American colleagues who work on this water project,” he says. “They are very good allies from the U.S. who we can deal with in regards to the crisis of water in the Colorado River.”

- Kent Paterson

Carlos de la Parra
Environmental Studies
Colegio de la Frontera Norte (Colef)
Tijuana, Baja California, Mexico
Tel: (619) 502-9189
Karl Flessa
Professor of Geosciences
University of Arizona
Tucson, AZ, United States
Tel: (520) 621-7336
Osvel Hinojosa-Huerta
Director of Water and Wetlands
Ensenada, Baja California, Mexico
Tel: +(521) 646-103-6166
Stephen Mumme
Professor of Political Science
Colorado State University
Ft. Collins, CO, United States
Tel: (970) 491-7428
Jennifer Pitt
Colorado River Project
National Audubon Society
Boulder, CO, United States
Tel: (720) 841-5366
Sally Spener
Foreign Affairs Officer
U.S. Section International Boundary and Water Commission
El Paso, TX, United States
Tel: (915) 832-4175