Print WEEK ONE: WHAT IS WATER? ESSAY ONE How the West was Watered: A Case Study of the Colorado River by Erin Vintinner Part One: The Mighty Colorado The dominant river of the American Southwest, the Colorado cuts a 2,250-kilometer (1,400-mile) swath from the snowpack of Colorado's Rocky Mountain National Park to the Gulf of California, draining water from Wyoming, Utah, Colorado, New Mexico, Nevada, California, Arizona, and Mexico. The Mighty Colorado The Colorado River winds through Glen Canyon in northern Arizona. James Phelps For thousands of years, Native Americans have lived along the river and used its waters. Spanish explorers provided the first written documentation of the river in the 16th century, and parts of the Colorado River's course were first mapped by the 1870s. Since the beginning of the 20th century, the river has fueled the development of what is now one of the fastest-growing regions in the United States. It supplies irrigation, hydroelectric power, and water to Denver, Phoenix, Tucson, Las Vegas, San Diego, and Los Angeles, and in the process has formed the basis of an estimated $1.2 trillion economy. Over 30 million people in the U.S. and Mexico depend upon Colorado River water every day. Its water goes to irrigating some 1.4 million hectares (3.5 million acres/14,000 square kilometers) of farmland, and to countless municipal, recreational, and industrial uses. The massive infrastructure along the river includes hydroelectric dams like the Glen Canyon and Hoover dams, along with 12 major reservoirs on the river and its tributaries. The two largest reservoirs, Lake Powell and Lake Mead, comprise 85 percent of the river system's storage capacity and can store about four years of annual flow. These dams and reservoirs have radically transformed the hydrology and ecology of the river, altering the river flows that created unique riverside habitat and trapping the nutrient-rich sediments that caused Spanish explorers to name it "Rio Colorado" ("the Red River") for the reddish-brown, silty quality of its water. Below the dams, the water now runs blue-green rather than red, and little sediment is deposited to replenish what the erosive force of the river carries away. Throughout most of the basin, ecosystems have been altered to a degree that threatens the region's unique wildlife and wilderness. The "Most Complicated Water System in the World" During the 20th century, as the American West was settled, water demands skyrocketed. In 1922, the seven basin states signed the Colorado River Compact, a document that to this day allocates every drop of river water to various stakeholders. Subsequent layers of regulation, collectively referred to as the "Law of the River," have combined to make the Colorado River the "most complicated water system in the world," in the words of the Pacific Institute's Peter Gleick. 1/5
Colorado River Basin 2/5
This map outlines the areas of the southwestern United States and Mexico that drain into the Colorado River, divided into the Upper and Lower basins. The river has three main tributaries: the Green, the San Juan, and the Little Colorado. Pacific Institute The Colorado River Compact divides the river into two basins (the Upper Basin in Colorado, Wyoming, Utah, and New Mexico and the Lower Basin in California, Nevada, and Arizona), and Mexico. The Law of the River states that both basins are entitled to 7.5 million acre-feet (maf) year, or 75 maf over a moving ten-year average. (An "acre-foot" equals one acre covered one foot deep in water, or enough to supply two households for a year also equivalent to 1.2333 x 10-6 cubic kilometers.) Mexico must receive 1.5 maf. Drought, Climate Change, and the River Federal agencies and water managers use historical data sets to model river flow. However, researchers are discovering that the years on which the Colorado River Compact was based were among the wettest of the 20th century and, according to tree-ring data, perhaps the wettest of the last 400 years. The average streamflow may in fact be 20 percent less than the flows between 1886 and 1921. During the drought of 2000 to 2006, the Colorado River had the lowest flows since gauges were installed. Nearly full in 1999, the basin's reservoirs declined to 40 percent capacity in 2005. The Rocky Mountain snowpack is the source of the river's water. Lighter snowfall or warmer temperatures could change the amount or timing of flows (reducing late spring flows, for example). Increased evapotranspiration (water evaporated from soils and plants) due to warmer temperatures could have the same effects. Lake Powell's purpose is to store surplus flows in order to regulate the Upper Basin's annual delivery requirement to the Lower Basin and Mexico. Lake Mead stores water released from Lake Powell in order to regulate deliveries to Lower Basin communities. The annual flow of the river combines with reservoir storage to provide the basis for yearly allocations, which are proportionally reduced in low-flow years when maximum withdrawals are impossible. Flow is measured by the Lees Ferry stream gauge, which is located in Arizona on the dividing line between the basins. The United States Bureau of Reclamation built the requisite infrastructure and oversees its management. Rising Demands, Diminishing Supply Depending on the amount of melted snowpack at its headwaters, the streamflow of the river varies. The terms of the Colorado River Compact were based on flow levels from 1886 to 1921. However, those years turned out to be unusually wet (see Box 1). Set at unsustainably high levels, the 1922 river allocations continue to challenge water managers. For most of the last 40 years, the river has run dry before reaching the sea, a phenomenon now also afflicting many other major rivers. Reduced supply is coupled with increasing demand. For example, Las Vegas located in the driest valley of the driest state of the U.S. has become one of the nation's fastest-growing cities and gets 90 percent of its water from the river. Agricultural demands continue to rise, for produce ranging from hay in the Colorado Plateau to fruits and vegetables on the U.S./Mexico border. Currently, the Upper Basin states consume 4.9 maf per year of their 7.5 maf entitlement, while the Lower Basin has frequently approached its allotment and sometimes exceeded it. Annual Flow Volume Time-series plot of the annual flow volume (in millions of acre-feet) for the Colorado River at Lees Ferry. The dashed line is the linear trend for the period. Vertical bars and shading delineate drought periods. USGS 3/5
What About Groundwater? The Colorado River also provides groundwater to surrounding areas, although its allocation is not addressed by the Law of the River. Groundwater replenishes far more slowly than surface water and is vulnerable to pollution. Groundwater in the Lower Basin is already consumed at rates that exceed natural recharge levels by 1.24 maf annually, which directly affects the Colorado River Delta. This regional shortfall is compounded by the state of the Mexicali aquifer beneath the Mexicali Valley near the U.S.-Mexico border, which farmers have already overdrawn. Any solution is complicated by the fact that groundwater management tends to be after-the-fact, because the water is often over-appropriated before the consequences become evident. Groundwater depletion poses risks to all stakeholders. These include a lower water table and reduced contributions to streams, rivers, and wetlands. Any regulation will require individual stakeholders to give up water rights. A Dilemma Compounded by Problematic Policy The combination of unsustainable river allocation levels, rising rates of extraction, and climate change raises the specter of a "compact call." In this politically charged scenario, if water levels drop so that the Lower Basin states receive less than their allotment of 7.5 maf, they could legally force the Upper Basin states to reduce consumption. In 2006, all seven states took preemptive steps by drafting the first-ever strategy for modifying water deliveries during shortages. This plan, which required three years of intense negotiations, took effect in 2008 and reduces the likelihood of a compact call. The next round of negotiations will start in 2020. The dilemma is exacerbated by the fact that water is heavily subsidized. With little incentive to conserve, users tend to adopt "use it or lose it" policies that perpetuate rights originally secured on a first-come, first-served basis. New cities must purchase these precious senior rights from agricultural districts. New water users who rely on groundwater confront dropping water tables. Unless extraction is limited, each new well puts further pressure on a declining resource. Part Two: What Are the Tradeoffs? The complex of treaties and agreements known as the Law of the River tightly controls how water is allocated among stakeholders. One of the thorniest issues is the legal status of Native American claims, which involve large quantities of water. There are few options for increasing the water supply. Las Vegas, for example, relies on banking, trading, reusing, and buying water rights to sustain its growth, while cities in Southern California are increasingly purchasing water from farms. These out-of-basin transfers through massive conduit systems do not return water to the Colorado River streamflow. The Effects on Water Quality and Native Species The Colorado River System is naturally very saline; approximately 9 billion kilograms (9 million tons) of salt flow past Hoover Dam each year. Water consumption (which reduces the amount of water that dilutes the salt) and salt influx from runoff further boost salinity levels. While the use of water for logging, mining, and urbanization all increase salinity, agriculture is the greatest culprit. Irrigation water dissolves salts in soils. When the water evaporates or crops consume water through evapotranspiration, these salts are left to accumulate in fields, creating one of the basin's most devastating forms of water degradation: salt pollution. Drought plays a part as well. A key impact of this pollution is economic, primarily from reduced crop yields and damage to pipes and fixtures. Reservoir eutrophication (dense plant and algal growth because of excess nutrients in the water, which kills other organisms by depleting oxygen levels) and contaminants from agricultural and industrial processes also affect water quality. Completed in 1964, the Glen Canyon Dam drastically altered the ecology of the Grand Canyon. For example, naturally occurring floods that once deposited sediment on sandbars and stimulated the germination of native plants no longer occur. As a result, sandbars that support native vegetation and animals, provide recreational opportunities, and buffer cultural and archeological sites, are being eroded. Sitting for long periods in the depths of Lake Powell also cools the river water to a uniform temperature and eliminates seasonal fluctuations. These changes harm native fish species, such as the endangered humpback chub (Gila cypha) and the razorback sucker (Xyrauchen texanus), which had adapted to the Grand Canyon's unique conditions. The dam itself blocks migratory routes for fish adapted to the original dynamic flow. More than 40 nonnative species, including trout and pike, have been introduced into the upper parts of the river for sport fishing. Many of these introduced species thrive in the cooler, clearer water and prey on the larvae and juveniles of native species. Government initiatives to protect endangered species must compete with the value of approximately 43,000 terajoules (12 billion kilowatt-hours) of electricity that the network of dams along the river provides to basin residents. The Delta Dries Up The Colorado River once emptied massive quantities of fresh water into the Gulf of California. After the Hoover and Glen Canyon dams were built, the river's flow was captured in Lake Mead (which filled from 1935 to 1957) and Lake Powell (from 1964 to 1981). Except on a few limited occasions, no water flowed beyond Morelos Dam, on the border between the U.S. and Mexico, from 1960 to 1980. The delta dried up, with drastic consequences for key riparian (interface between the river and land), wetland, and estuarine (interface between river and ocean) 4/5
habitats, as well as for coastal fishing and farming communities. The local shrimp industry has been decimated by overfishing and also by the lack of freshwater influx. At the River's End This graph shows the Colorado River's annual flow volume as recorded at the pump station in Yuma, AZ from 1903-2003. The inset graph shows the same volumes during 1991-2002. USGS Since Lake Powell, the last major reservoir built on the river, filled in 1981, flood flows released by U.S. water managers in the United States have partially revegetated the delta. (These releases occur during El Niño cycles when flows are higher; during dry years, no water reaches the delta.) Migratory birds such as the endangered Southwestern willow flycatcher (Empidonax traillii extinus) have benefited, as have shrimp populations and some species of fishes, including the Gulf corvine (Cynoscion othonopterus), a commercially valuable fish endemic in the upper Gulf of California. Irrigation for approximately 200,000 hectares (500,000 acres) in the Mexicali Valley currently dominates the water usage agenda. Conservationists are exploring measures to further protect natural areas in the lower delta in Mexico and the adjacent marine zone. Agricultural runoff, mostly from the Wellton-Mohawk Irrigation District in Arizona, has drained into the delta since 1977 via an 80-kilometerlong (50-mile) concrete-lined canal, creating the area's largest wetland, the Cienega de Santa Clara. Situated within the Colorado River Delta Biosphere Reserve, the wetland contains the largest remaining population of the endangered Yuma clapper rail (Rallus longirostris yumanensis), plus numerous species of waterfowl. Later in the course we'll investigate how new technologies and conservation measures are addressing these challenges in the southwestern United States. Related Links USBR: The Law of the River» Browse through the significant documents that explain the management and use of the Colorado River among the seven basin states and Mexico. USBR: Current Water Levels» Up-to-date reports on the water levels in the Upper Colorado River Basin. NGM: Drying of the West» Article about the water management crisis of the American West. NYT: The Future is Drying Up» Article looking at the fastest-growing part of the United States and its impact on the water system. 5/5