A Decades-Long Tug-of War over Water

Posted: 01-Mar-2003; Updated: 20-Jun-2003

Over the course of millions of years, water and silt from the Colorado River Basin flowing downstream to the Gulf of California created one of the greatest desert deltas the world has ever seen. During the past century, efforts to harness Colorado River water, primarily for agriculture but also municipal uses and hydroelectricity production, have radically reshaped, or more accurately, decimated the delta. Upriver water management policies favoring consumptive use of the resource have greatly reduced the amount of water and silt reaching the delta, causing drastic, damaging changes to the physical characteristics of the landscape. As a result, the plants and animals that adapted over large periods of time to this vibrant, yet temperamental and unforgiving environment have suffered mightily. The Cucupá Indians who survived for some 2,000 years off the rich and diverse biota of the region consequently find themselves no longer able to do so.

The seeds for change were sown in 1901 when prospectors attempted to irrigate the desert lands of the Imperial Valley in southern California by diverting water through a privately built canal. Shortly thereafter, the swollen river revealed its true force, smashing through the canal and forging its own path before accidentally creating the Salton Sea. Undeterred, the powerful Imperial Irrigation District gained the support of the Bureau of Reclamation in 1921, calling for a more capable water delivery system to aid the flourishing agriculture businesses of the area. The Boulder Canyon Project Act included construction of what was then the world's biggest dam, known today as Hoover Dam, and behind it, Lake Mead, America's largest man-made storage reservoir.  

However, those upriver of the chosen location, the Black Canyon on the Nevada-Arizona border, were unwavering in their resistance to the plan. Their opposition centered on existing water law, commonly referred to as "first in time, first in right," which simply means that whoever uses water first gets the rights to it. With a storage reservoir able to deliver water like clockwork, those below the dam would be able to use more water, thereby establishing rights to it at the expense of upriver interests who wished to have access to it in the future.

To resolve the conflict, the Colorado River Commission, with representatives from the seven states using Colorado River water, formed at the end of 1921 to negotiate a settlement ensuring the upriver users their fair share of the water in exchange for congressional support of the dam. In 1922, after ten contentious meetings, an agreement known as the Colorado River Compact was reached, dividing U.S. river users into an Upper Basin and a Lower Basin with each basin granted an equal share to be divided among their member states.

Unfortunately, the Compact was fatally flawed by a significant overestimation of the Colorado's average annual flow. Based on calculations from a wetter than normal time period at the beginning of the 20th century, the volume was assumed to be 18 million-acre feet per year (maf/y). In fact, the river's average flow is 13.5 maf/y. This miscalculation has haunted water management efforts ever since and promises to become even more problematic as those not yet using their full entitlements attempt to do so. With each of the basins granted 7.5 maf/y in the 1922 Compact, and Mexico guaranteed 1.5 maf/y in a 1944 treaty, as it now stands 16.5 maf/y has been allocated with only 15 maf/y existing. As other needs for water have become painfully obvious, such as those for maintaining the health of the delta's ecosystem, water managers and users will have to become increasingly efficient and creative to meet the many demands on this precious, but finite and severely overburdened resource.

Building Hoover Dam

When Hoover Dam was completed in 1935, the reservoir behind it started to fill, and for six years nearly all Colorado River water not scheduled for off-stream deliveries was captured.  For the first time, the Colorado River delta experienced a significant reduction in freshwater flows.  

By the mid 1950's, states in the slower-growing Upper Basin were getting more and more concerned over the increasing use of water in the Lower Basin, particularly in California, and began pushing for construction of yet another series of storage dams. Aware that the river was over-allocated, and not wishing to pit their 1922 Compact allocation against the well-established "first in right, first in time" water law, the Upper Basin states sought their own storage facilities.

The Colorado River Storage Project Act, passed in 1956, authorized construction of four major dams and reservoirs on the upper Colorado and its tributaries. The gates were closed on the Glen Canyon Dam, the largest of the four, in 1963.  For nearly two decades the reservoir behind it filled with Colorado River water, again depriving the delta of nearly all flows. 

Not surprisingly, the delta's ecosystem starting drying up. Plants and animals dependent on freshwater were either unable to cope with the radically changed environment or choked out by invasive nonnative species better suited to the new conditions. In addition to being deprived of water, nutrient rich silt that once formed the critical base of the complex delta ecosystem was now trapped behind the upriver impoundments. A defining geological process was reversed: instead of accumulating soil deposits, as it had for thousands of years, the delta soils began to erode, significantly reducing the amount of valuable habitat. What Mother Nature had taken great care and time to create was being eradicated almost overnight by management decisions failing to take into account the full range of consequences of their actions. 

El Niño and Other 'Godsends' Bring Relief

During the 1980's, El Niño weather patterns resulted in heavier than normal snowpack throughout the Colorado River Basin. With storage reservoirs kept filled to capacity to maximize hydroelectric output and to protect against drought years, small sporadic amounts of floodwater returned to the delta. The 1990's were not as wet as the preceding decade and less water reached the delta.  Nevertheless, some of the ever-resilient native delta species have shown a remarkable ability to sustain themselves on flood flows that occur only every few years. Because these small, yet invaluable periodic flows are not specifically designated for the delta, the risk that they will be eliminated is real.

Another source of water inadvertently came to the delta as the result of the agriculture industry in southern Arizona in 1961. When wastewater from the recently developed Wellton-Mohawk Valley drained into the river, it rendered the Colorado's water too salty for use downstream in Mexico, killing thousands of acres of crops south of the border, and Mexico protested. The 1944 treaty with Mexico was eventually amended with a water quality provision, and the U.S. agreed to meet its delivery obligation with a more usable supply of water. To this end, the salty water draining from the Wellton-Mohawk district was routed away from the Colorado River in a canal that terminates in what was at the time a desiccated arm of the Colorado River delta. In the meantime, the offending water unexpectedly created one of the delta's most productive existing wetlands, the Ciénega de Santa Clara.

When the U.S. federal government agreed to meet the salinity standard for Mexico, it promised water users in the U.S. that it would replace the water diverted away from the river.  To meet this requirement, the government built a desalination plant in Yuma, Arizona with which it planned to treat the salty drainwater and return it to the river.  In 1992, the desalting plant began operating at one-third capacity but has since remained idle due to the unreasonably high cost of the process. As a result, this water, too poor in quality for human consumption, continues to reach the delta where it sustains a lush, open-water wetland. But like the recently returned flood flows, this water is not specifically earmarked for the delta and could be used elsewhere in the future. If this happens, the already struggling delta would lose a critical piece of recovering habitat.

The priceless delta faces an uphill battle in the fight for Colorado River Water and ultimately its survival. At present, the Law of the River, a complex set of legal and administrative agreements governing Colorado River water rights, places environmental protection dead last on its list of priorities. And while the Colorado River might be considered by many to be a public resource, the water that flows in it is now completely owned and consumed. Until the Colorado River "owns" some of its water, with dedicated rights to instream flows, the delta is sure to disappear. 

View our slideshow Hope for the Colorado River Delta

Another Step Forward for Restoring the Colorado River Delta (10/22/2002 article)

Mapping Conservation Strategies in the Colorado River Delta: A State-of-Knowledge Workshop (October 15-17, 2002)
A Delta Once More (1999 report from Environmental Defense)

University of Arizona web site