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Deciding About the Colorado River Delta

Rejuvenated Wetlands Raise New Issues About Where Flood Flow Should go

River Report, Water Education Foundation, Spring 1999, pp.1,4-9,11
By S. Joshua Newcom*

It starts as a trickle in the mountains of Colorado - snow and ice melting to the demand of rising temperatures. Tumbling thousands of feet, the alpine water melds into a succession of creeks, springs and rivers, forming the waterway known as the Colorado River.

Before the creation of state and international boundaries, the unchecked Colorado wound its way through the southwestern corner of North America and into what is now known as Mexico. There, a combination of nutrient-rich water and silt from the river created widespread wetlands - at times extending from southern California where the Salton Sea is today to the northern tip of the Gulf of California (gulf). Bordered by mountains and desert, the historic delta comprised over 2.5 million acres of wetlands and provided habitat for an estimated 400 species of plants and wildlife. Along its shores, some 20,000 Cocopah Indians made a life from the ecosystem by fishing, hunting and farming. The area became known as the Delta del Rio Colorado - the Colorado River Delta.

Cienaga de Santa Clara

With completion of Hoover Dam in 1935, the United States began damming the Colorado River - on a much larger scale than in the past - to meet the needs of burgeoning cities and farms in the West. Nearly 30 years later, the last of the great dams on the Colorado River was completed when the gates of Glen Canyon Dam closed in 1963. Mexico, which at one time received the full flow of the Colorado, agreed to an annual delivery of 1.5 million acre-feet (plus up to 200,000 acre-feet in surplus years) of water under the Mexican Water Treaty of 1944, all of Mexico's river apportionment is typically consumed by agriculture and municipal industrial (M&I) uses in the Mexicali and San Luis valleys.

Thus, in a normal water year, the last drop of the Colorado River evaporates in Mexican sands - about 1,450 miles from its birth and short of its natural termination in the gulf.

Increased public interest in environmental issues over the years has substantially boosted attention to the delta from governments, non-governmental organizations (NGOs) and environmental groups on both sides of the border. According to U.S. fish & Wildlife Service (USFWS) figures, over half of the wetlands in the United States have disappeared since 1780. And according to the California resources Agency, California, a major stopover for birds along the Pacific Flyway, has only 10 percent of the wetlands that existed before European settlement. The short-fall is this rich habitat has led some to see Mexico's delta as a potential saving grace.

Nearly two decades of heavy rain and snowfall, as well as the filling of Lake Powell, have boosted river flows into Mexico. The Colorado River has reached the gulf five times since 1983, most recently in 1998. Wetlands in the region have benefited from the flood flows that have regenerated vegetation and fish and wildlife populations. Sections of the delta and the northern gulf support several endangered species like the totoaba, a fish species once used commercially and for sport fishing; the vaquita, the world's smallest propoise and rarest ocean mammal; the desert pupfish; and endangered species of birds such as the southwestern willow flycatcher and the Yuma clapper rail.

Questions now abound about if and how to maintain and enhance these vital wetland ecosystems, but a solution - like anything on the Colorado River - is far from easy. In an act of protest, two environmental groups within the United States have bowed out of a steering committee for the Lower Colorado River Multi-Species Conservation Program (LCRMSCP) claiming the program falls short of addressing environmental needs in the Mexican delta.

The LCRMSCP is an environmental management plan for the Lower Colorado River being implemented by the Bureau of Reclamation (Bureau) in cooperation with the USFWS, the Lower Basin states, Tribes and National park Service. (See Winter '98 River Report.)

The Colorado River flows to the Gulf of California only in extremely wet years.

"Eighty percent of the top Lower Colorado River habitat is in Mexico," said Tom Larousek, a conservation associate with American Rivers (one of the letter's signatories), an organization that listed the Colorado River Delta as one of its top 10 endangered rivers in North America in 1998. "It is a biological reservoir of sorts and if you enhance that habitat, you enhance the recovery of species all the way up the Colorado River into the U.S."

But state interests and the United States government remain cautious about supplying more water to Mexico. "We don't have any jurisdiction over how Colorado River water is used once it crosses over the border into Mexico," said Robert Johnson, regional director for the Bureau's Lower Colorado Region.

This issue of River Report examines the complexities surrounding the Colorado River Delta, its ecological importance, the issues that impact it and what is being done internationally to preserve and enhance its existence.

Brief history of the delta

Before humans began to build cities, farm western soil and dam the Colorado, the delta was as untamed and wild as the river that fed it. During a boating journey down the Colorado River Delta for sunset Magazine in 1923, journalist Lewis Freeman remarked: "At the time of which I write, indeed, it is probably that no place in the world with the exception of the removed regions of Africa harbored so great a variety of wildlife." Nearly 80 years later, the delta is a very different place, primarily due to agricultural development and changes to both water quantity and water quality resulting from controlled river runoff.

Prior to the completion of Glen canyon Dam, between 4 and 6 millions acre-feet of Colorado River water still inundated Mexico's wetlands in a normal water year. Today, flows only reach the delta in very wet years. El Niño created a succession of these wet years on the Colorado River system from 1983-87 and once again, waters flooded the delta, scrubbing floodplains, spreading tree and plant seeds and soaking lands that had not been touched directly by the river's water in nearly two decades.

Since the turn of the century, about 150,000 acres of wetlands in Mexico have been converted into agricultural fields. Levees built by the Mexican government to prevent flooding of farmlands follow the Colorado River from Morelos Dam to the Gulf of California. The levees channel these flows and have essentially created a revitalization of natural wetlands in parts of the delta during abundant water years.

In 1993 the government of Mexico declared 2.3 million acres of water and land in the Northern Gulf and parts of the delta as the Reserva de la Biosfera del Alto Golfo de California y Delta del Rio Colorado (Biosphere Reserve) - a region of habitat managed and protected by the Mexican government. The reserve, 80 percent of which is aquatic, includes portions of the Rio Hardy wetlands and the Cienega de Santa Clara (Cienega) in the deltas. Activities in the core zone - about 400,000 acres - are limited to research, small-scale shellfish harvesting and low-impact ecotourism. Some in the United States view this protection of fish and wildlife habitat as an indication of Mexico's commitment to ecosystem preservation.

"Part of the Reserve's core zone extends into about 72,000 acres of the delta," said José Campoy, director of the reserve, " and one of the major concerns of the reserve is obtaining more fresh-water flows."


In the past year, the delta has been the subject of two reports: "Importance of United States' Water Flows to the Colorado River Delta and the Northern Gulf of California, Mexico" (Glenn and Valdes-Casillas, October 1998) and "Wetland Management & Restoration in the Colorado River Delta: The First Steps," (North American Wetlands Conservation Council, November 1998). The reports are collaborative efforts between academic institutions and NGOs in Mexico and the United States.

The studies make two strong assertions about what could be done to improve the region:

  • The most valuable native riparian habitat is in the 150,000-acre core of the delta, and
  • The delta can be sustained with relatively marginal annual instream flows and periodic flooding.

In all, the reports conclude that the Mexican delta contains nearly twice the riparian habitat and marshland found along the adjoining stretch of river in the United States from Davis to Morelos dams including cottonwood-willow forest, flood plains and emergent wetlands.

Cienega De Santa Clara

One wetland in the delta is an anomaly to the rest, existing regardless of instream flows from the Colorado River: The Cienega de Santa Clara (Cienega).

In the 1970s, the Cienega comprised less than 500 acres, the result of natural artesian springs, tailwater (agricultural runoff) from surrounding agricultural lands in Riito and occasional high tides or storm surges from the gulf. Today, the Cienega has expanded to cover approximately 15,000 acres of dense vegetation, due almost entirely to agricultural return flows from the Wellton-Mohawk Irrigation and Drainage District (WMIDD) across the border in the United States. WMIDD diverts approximately 400,000 acre-feet of Colorado River water annually to irrigate crops. Already salty Colorado River water, combined with the saline soil of WMIDD farmlands, creates a saline groundwater supply. As the underlying groundwater basin fills with water from the irrigated fields, salts are pushed to the surface. To keep the salts below the root zone, pumps remove about 120,000 acre-feet of brackish groundwater annually.

Initially, the saline groundwater pumped from WMID farmlands was blended with Colorado river water going to Mexico. but Minute 242, negotiated in 1973 (an addition to the '44 Treaty), curbed the amount of salts allowed in credited water deliveries over the border. To desalinate the Wellton-Mohawk drainage water before its delivery to Mexico, the Bureau constructed the world's largest reverse osmosis water treatment facility in Yuma, Ariz. At a construction cost of $250 million, the Yuma Desalting Plant is designed to treat up to 96,000 acre-feet of water annually.

During construction of the treatment plant, a $45 million drainage canal was constructed in 1977 to dispose of the brackish WMIDD groundwater until it could be treated by the plant. The bypass drain transports the salty drainage water 50-miles south into the Cienega. (This water does not meet international salinity requirements and is not counted towards Mexico's Colorado River apportionment.)

To date, the Yuma Desalting Plant has never been fully online. It operated at one-third capacity of nearly a year, but a flood on the Gila river in 1993 washed out a section of the drainage canal, halting operation. In the meantime, the Yuma Desalting Plant is being kept in "ready reserve" at a cost of $6 million a year. the possibility of operating the plant looms closer as water use on the Colorado continues to grow.

"There is recognition that operation of the desalting plant will decrease the quantity and increase the salinity of the water traveling to the Cienega," said William Rinne, are manager for the Bureau's Lower Colorado Region. "I would expect the Cienega to become more limited in terms of what it could sustain," he said. Rinne said that bypass drain would still be used to discharge the salty byproduct of the desalting plant to the Cienega.

Additionally, the reports conclude that riparian habitat mitigation can be sustained with a relatively nominal amount of water annually - perhaps less than 1 percent of normal river flow, augmented by treated wastewater streams and occasional flood releases.

"Because the primary water needs in the delta are intermittent, it doesn't require huge amounts of the river's annual flow,," said Edward Glenn, a professor in the Department of Soil, water and Environment at the University of Arizona and one of the lead scientists in the studies. "Around a half-million acre-feet of water every three to four years would probably take care of riparian habitat for the region."

Using satellite photos, aerial videography and photos, ground surveys and extensive on-site work including vegetative analysis and mapping, water quality analysis and community outreach, the group of researchers compared high-flow years in the delta with low flow years.

The studies estimate that the delta's core can be flooded with about 256,000 acre-feet of water, a process important to germination for the delta's vegetation, according to Glenn. This number was achieved by examining the records of flows through Morelos Dam and a comparison of delta vegetation during those corresponding flows. The studies showed trees were able to continue growing during three or four successive years of receiving no water, thus concluding that overbank flooding of the delta core is needed every four years to sustain existing vegetation and that more frequent floods could expand the scope of the riparian zone. Approximately 32,000 acre-feet of inflows annually to the delta are sufficient to maintain the cottonwood-willow gallery forest, a habitat capable of supporting a wide variety of birds and wildlife.

Although the Bureau is interested in information about the ecology of the delta, officials remain cautious about the flow requirement findings in the reports.

"At present, it is difficult to evaluate the accuracy of the estimates because there is not a good understanding of how the data was generated and the assumptions made about conditions which existed within the river corridor preceding these flow events," said William Rinne, area manager for the Bureau's Lower Colorado Region.

To help solidify the answers, a joint effort is underway between USFWS and universities in the U.S. and Mexico to conduct field studies of wildlife and vegetative counts in the delta.

"The delta is one of the most important migratory routes in all of North America," said Charlie Sanchez, associate regional director for international affairs with the USFWS. "We have to leave a legacy in the protection of these resources."

Sanchez said he is working with affiliates in Mexico and the United States to conduct population assessments of species like the Yuma clapper rail and the desert pupfish,to assess the riparian values of delta wetlands areas and to map those areas.

So far, Sanchez said Interior has spent around $909,000 to initiate the studies.

Glenn said some of the information will be incorporated into a third study planned for publication later this year that makes specific recommendations for managing habitats in the delta region.


There are those who would like the United States to be required to release Colorado River flows for the environment, including the delta. But this idea has sparked considerable debate among policy makers because of legal constraints and the lack of additional water.

"Water and power agencies in the U.S. want all Colorado River water for use in the U.S. and refuse to allocated any for conservation purposes," said David Hogan, river program coordinator for the Southwest Center for Biological Diversity, an environmental group based in Tucson, Ariz.

The Southwest Center, along with Defenders of Wildlife, pulled out of a process to develop a LCRMSCP - the management plan for fish, wildlife and habitat on the U.S. portion of the Lower Colorado River - because the plan would not address the Mexican delta.

The Yuma clapper rail is one of the delta's endangered species.

In March 1999, a letter was addressed to Interior Secretary Bruce Babbitt from the Southwest Center and eight other organizations expressed their dismay over what they consider to be shortcomings of the program.

"Conservation planning that stops at geopolitical borders without regard for ecosystem boundaries and sound conservation biology principles is domed to fail," they wrote. The letter also condemns a resolution passed by the Colorado River Board of California stating its desire to limit the LCRMSCP to the United States.

Salton Sea

"We must also come up with a solution about how to approach Salton Sea restoration in a way that isn't detrimental to the Delta, " said Jason Morrison, a senior associate with the Pacific Institute.

The February 1999 Pacific Institute study, entitled "Haven or Hazard: The Ecology and Future of the Salton Sea" recommends that restoration plans for the 35-mile long Salton Sea be coordinated with restoration efforts in the delta. Part of the same historical basin, the report denounces proposed restoration alternative that would divert Colorado River flood water away from the delta to the Salton Sea or pump in potentially harmful brine water from the Salton Sea somewhere near the delta.

But not everyone agrees with the Institute's recommendations.

"In a perfect world, barring political, practical and economic considerations, the ecology of all these places would get comprehensively studied and managed," said Tom Kirk, executive director of the Salton Sea Authority. "We do not live in a perfect world."

Kirk went on to say that due to time constraints under the Salton Sea Reclamation Act of 1998, scientists working on the sea must make recommendation to Congress by January 1, 2000.

"It was the board's opinion that with the limited time and money available to us, what we need to do now is focus on developing the LCRMSCP within the U.S.," said Gerald Zimmerman, executive director of the Colorado River Board of California. Currently in development, the 50-year LCRMSCP is expected to be ready for implementation by 20001. "There is the adaptive management component of the LCRMSCP that encourages the exchange of information between U.S. and Mexican officials and could allow for expansion into the delta once the LCRMSCP is implemented," he said.

Under a separate effort, a coalition of U.S. government departments and agencies, and their Mexican counterparts, have entered into discussions with the Mexican government via the International Boundary and Water Commission (IBWC). The IBWC is the arm of the U.S. government that handles issues associated with water deliveries to Mexico such as the availability of water and when such water can be delivered.

"Discussion of restoring the delta was added to our agenda about a year ago," said John Bernal, commissioner for the United States Section of the IBWS. Bernal said the IBWC has facilitated one major meeting and several technical -level working sessions with various U.S. and Mexico federal and state agencies to determine what still needs to be gathered. "We are addressing the challenge of assuring conditions in the delta do not deteriorate any further and that preferably valuable resources are sustained," he said.

In May 1997 - the same year work began in earnest on developing the LCRMSCP - Babbitt and Julia Carabias Lillo, Mexico’s secretary of Environment, Natural Resources and Fisheries, signed a Letter of Intent in which their "two agencies plan to expand existing cooperative activities in the conservation of contiguous natural protected areas in the border zone, and to consider new opportunities for cooperation in the protection of natural protected areas in the United States-Mexico border." The letter was the latest in a series of agreements between the countries intended to augment binational protection and enhancement of the border environment through an exchange of scientific information, community outreach programs and joint studies.

But for the Southwest Center’s Hogan, the time for increased water deliveries to Mexico is now. He said that center could sue to try and get committed river flows for the delta by proving the United States is responsible for endangered species protection in Mexico. "It’s a simple issue of encouraging the U.S. to take responsibility for the effect of exploiting the river," he said.

Supplying the delta

If it were determined that more water should be given for the delta, how to increase those allocations to Mexico without reopening the Law of the River is considered by many to be a major undertaking and one that could involve massive litigation. The 1922 Colorado river Compact only allocated water to seven U.S. states and, despite subsequent state, federal and international agreements, treaties, court decisions and legislation, the environment is only recognized as a limited "user" of the Colorado River. (Water was allocated under the 1968 Colorado River Basin Project Act for a number of wildlife refuges within the basin.)


Over 200,000 people live in the delta area (not including Mexicali), members of what remains of the Cocopah Indian tribe near El Mayor, a tributary to the Hardy River. Part of the equation for restoring the delta is to involve these communities in discussions about the delta. Goals of an outreach program organized and funded by the North American Wetlands conservation Council, a coalition supported by federal, academic and nongovernmental entities include:

  • Identifying stakeholder groups;
  • Explaining restoration possibilities and determining if the stakeholders are interested in participating;
  • Bringing stakeholders, local government leaders, research centers, academics, NGOs and policy makers to the table and facilitate discussions about what everyone's needs from the delta are; and
  • Conducting workshops and conferences to discuss restoration plans and implementation.

"Part of the niche we are trying to fill in the absence of community leaders in modifying and changing the use of water in the delta," said Steve Cornelius, director of borderlands program for Tucson-based Sonoran institute, one of the participants in the program. "Managing the delta has to be beneficial to the communities using the water."

Cornelius said he expects the process, which has been spearheaded in the Rio Hardy Wetland area, to take up to seven years to complete. "We need to understand what the various stakeholder positions are and they need good, solid, scientific information in order to design a position," he said.

Carlos Valdés-Cassillas, director of the Center for Conservation and Use of Natural Resources at the Monterey Institute in Guyamas agrees.

"The best possibility for accomplishing a management plan for the delta is to look at a more effective use of water including reuse of agricultural run-off and additional instream flows during flood years," he said. "We must look to different institutions and water users to partake in the responsibility."

Other groups taking part in the process include Pronatura Sonora, the University of Arizona, California State University, Dominguez Hills and the Environmental Defense Fund.

A variety of programs and treaties have been implemented over the past 50 years to address border issues, but none has dealt specifically with the delta region. The Border XXI Program and North American Free Trade Agreement are two examples of major binational agreements that include environmental provisions, but neither has the authority to allocate more Colorado River water for the delta.

For parties in the United States, a major concern of allocating greater flows to Mexico is a lack of certainty over how water intended for environment would be used. The Mexicali Valley relies on the Colorado and Gila rivers for nearly 100 percent of its water supply. Preliminary calculations by the Pacific Institute in its 1996 report "The Sustainable Use of Water in the Colorado River Basin" indicate that the Mexicali Valley is suffering from a groundwater overdraft of roughly 96000 acre-feet annually. The overdraft could become even greater with the added lining of the All American Canal north of the border - a source of groundwater recharge for Mexico. Mexico's desire for more water has given rise to fears that increased flows to Mexico would be used to recharge goundwater overdraft or to irrigate fields in Mexico instead of as instream flows for the environment.

One proposed method for earmarking additional flows to Mexico for instream purposes is amending the existing Law of the River. Some have used Minute 242, the addition to the 1944 Treaty with Mexico that improved the quality of water deliveries to Mexico, as an example of a potential way to permanently mitigate water for fish, wildlife and habitat in the delta. Similarly, some purport that a like measure could modify the Colorado River Basin Salinity Control Act of 1974 to ensure continued deliveries of equal or better quality water to the Cienega.

The Colorado River Delta in a Glance

The Riparian Corridor (1)

Bordered by farmland levees. Stretches about 70 miles from Morelos Dam to the junction with the Hardy River. Contains large stands of cottonwood and willow trees measuring 13-feet to 50-feet tall, from high water in the 1980s and saplings from recent floods in 1993 and 1979.

The Rio Hardy Wetland (2)

Maze of sloughs and old river channels and confluence of the Hardy and Colorado rivers. High salinity levels in area due to high tides from the gulf 35 miles away, geothermal wells and agricultural drainage. Some cottonwood and willow trees in northerly portion giving way to more salt-tolerant vegetation including, salt cedar, mesquite, areas of Palmer’s saltgrass and cattails. Once a natural earthen dam located 21 miles northwest of gulf created a natural 45,000 acre floodplain that grew to 160,000 acres with ‘80s upstream releases. Wetlands shrunk to 3,000 acres after dam breached by floods. Ducks Unlimited studied rebuilding the natural dam, but determined frequency of flows too few and of poor quality.

Laguna (3)

Only during very wet years does water reach this salt flat. In majority of years, area looks like a desert plain.

Cienega de Santa Clara (4)

Largest and one of the most biologically rich delta wetland areas. Supported by brackish agricultural flows in the U.S. and Mexico and natural artesian springs. Supports large populations of endangered desert pupfish and Yuma clapper rails.

El Doctor Wetlands (5)

1,700 acre wetland fed primarily by natural springs. Area biologically rich and believed to contain over 22 different types of plant species and endangered desert pupfish.

El Indio Wetlands (6)

Covers over 4,000 acres fed by return flows from surrounding San Luis farmlands. Agricultural flow once followed a drainage channel back to the river wetlands but around 1993, the drain was damaged and flows spilled outside the flood plain. Typical regional coastal wetlands vegetation, primarily salt cedar, mesquite, Palmer’s grass and cattails.

Intertidal Wetlands (7)

Mudflat much of the time, though an estuary during we years. 13 mile-long section provides - at times - spawning habitat for numerous species, including corvina, totoaba and shrimp. Easily disrupted by a lack of fresh water, creating water too saline to support the propagation of many species.

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