The tension between aridity and irrigated agriculture has been a defining characteristic of Colorado for much of its modern history. On average, the state receives less than fifteen inches of annual precipitation, making it the seventh driest state in the country. To complicate matters, the majority of the state’s water originates in basins that are not suited for agriculture, making access to water not just a question of quantity but of engineered distribution. Consequently, Colorado farmers, politicians, and businesses developed sophisticated irrigation systems and complex laws for capturing, storing, and moving water from source to field.
Though irrigation in the West has been practiced for over a millennium, its continuous use in Colorado stems from the mid-1800s. Beginning in 1852, descendants of Spanish settlers near the town of San Luis built community-owned ditches known as acequias, which diverted water from the Rio Grande and its tributaries. The next significant irrigation effort occurred near the confluence of the Cache la Poudre and South Platte Rivers, where settlers established the Union Colony of Colorado. The colony’s success was predicated on irrigation sufficient to grow high-value crops. Despite higher-than-expected costs and poor planning, the colony—later named for cofounder Horace Greeley, editor of the New York Tribune—built twenty-seven miles of canal in its first year, capable of watering 25,000 acres. Following the Greeley colony’s example, settlers in the region had appropriated every last drop of water in the South Platte watershed by the turn of the twentieth century. By 1900 extensive irrigation works watered fields in the Arkansas, Rio Grande, Colorado, Gunnison, Animas, and Yampa River watersheds. At the turn of the century, Colorado led the nation in irrigated acreage.
Precedent, scarcity, and economics pushed Colorado farmers to develop water laws that diverged from those of their eastern peers, who possessed the right to divert water from a natural stream only if it coursed through their land and if their diversion did not damage the rights of downstream users. By contrast, during the Colorado Gold Rush of 1858–59, miners diverted water from streams sufficient to conduct their operations. The right to divert water was not based on land ownership but on the order of their claim. Early water claims possessed priority over later ones. Farmers embraced that same “first in time, first in right,” or prior appropriation, doctrine, enabling them to divert water from streams on a first-come-first-served basis, regardless of the stream’s location. Prior appropriation was tested in 1874 when, in a drought year, Greeley farmers were unable to access sufficient water from the Cache la Poudre River because upstream farmers in Fort Collins nearly drained the river dry. The two sides were forced to come to an agreement that guaranteed Greeley its water based on its prior claim. Colorado’s 1876 constitution and the 1882 court case Coffin v. Left Hand Ditch Co. enshrined the doctrine of prior appropriation into law with one caveat: appropriators needed to demonstrate that they were putting water to beneficial use. Most states in the American West based their water laws on those established in Colorado.
Since the late nineteenth century, mutual irrigation companies have managed the majority of Colorado’s irrigation water. These companies issue stock to farmers; however, unlike stock traded on Wall Street, each share entitles the holder—generally, a farmer—to a volume of water in a given year. The amount of water attached to a share varies from one year to the next based on water available in streams and reservoirs and on the seniority of each company’s rights; senior appropriation rights guarantee more reliable flows than junior ones. To guarantee sufficient water, junior appropriators will often purchase water from others in low-water years to make up their deficit. This is only possible because the majority of canals, ditches, diversions, and reservoirs in the state are interconnected, which facilitates water exchanges.
Federal Measuring Projects
During the twentieth century, farmers, local boosters, and politicians prioritized making more water available and streamlining the delivery system. According to Elwood Mead, the first professional irrigation engineer in the state and a key figure in the federal Bureau of Reclamation in the early twentieth century, Coloradans in 1900 were taking as much as fifty times more water than they were allotted or could beneficially use. Without effective tools for water measurement, little could be done to regulate the system. As a result, the Colorado Agricultural College (CAC) at Fort Collins—now Colorado State University—and the federal Bureau of Agricultural Economics funded Colorado-based projects to accurately measure and distribute water. Ralph Parshall, perhaps the most influential of these irrigation engineers, developed tools for measuring water in streams and ditches to within 2 percent accuracy. This increased the amount of available water in Colorado streams by as much as 30 percent, a boon for junior appropriators who were often left high and dry in drought years. Parshall and his colleagues at the CAC also experimented with methods for removing silt and gravel from irrigation ditches, measuring snowpack to predict annual stream flow, and reforesting hillsides to slow spring runoff in attempts to make more water available later in the farming season. Still, Colorado farmers complained of insufficient water for their crops.
Transmountain Diversion Projects
Effective measuring did not entirely solve water shortages. Transmountain diversion—moving water from a watershed with abundant water and little agriculture to parched regions with developed agriculture—presented another solution. The first and largest of these—the Colorado-Big Thompson Project (C-BT)—was approved by Congress in the midst of the Depression and drought of the 1930s. Financed largely by the Bureau of Reclamation in 1937, it transferred 320,000 acre-feet of water annually from the headwaters of the Colorado River, on the west side of the Continental Divide, through a tunnel under the peaks of Rocky Mountain National Park and into Eastern Slope reservoirs and streams that fed agriculture in northern Colorado. C-BT water annually added the equivalent of the total flow of the Cache la Poudre River to the South Platte River watershed.
Subsequent transmountain diversion projects sponsored by Reclamation, such as the San Juan-Chama and Fryingpan-Arkansas Projects, transferred water from the Colorado and San Juan watersheds into the Arkansas and Rio Grande basins. In total, there have been more than thirty transmountain diversion projects in Colorado during the twentieth century.
Changes in Water Demand
Water thirst in Colorado has been fed not just by scarcity but by real estate and consumer markets. A cursory glance at land values and crop evolution offers evidence. While land values across the state have generally increased in Colorado throughout the twentieth century, they rose most rapidly in irrigated lands. The costs of land and water on those lands, as well as property taxes, encouraged farmers to plant crops of high market value. In the early twentieth century, the most lucrative crop on the Western Slope and in the Arkansas and Platte River valleys was the sugar beet, a vegetable requiring extensive irrigation. In the 1930s and 1940s, when new hybrid corns were developed that were better suited to the short growing season of the state’s eastern plains, farmers prioritized corn, which required even more water than beets.
On the Western Slope, hardy varieties of peaches—another water-loving crop—pushed farmers on irrigated lands to plant orchards. In the San Luis Valley, where aridity and high elevations demanded crops that could withstand a short growing season, farmers prioritized potatoes, alfalfa, hay, barley, wheat, and lettuces.
The post–World War II era has challenged Colorado’s limited water supply. After massive population increases—especially on the arid Front Range—municipalities demanded more water. This has enticed farmers and ditch companies to sell their lucrative water rights to growing municipalities and construction companies offering high prices, resulting in housing developments on land formerly used by farmers.
Other parties seeking water rights include oil and gas companies, which often lease farmland for drilling and then employ purchased water rights to extract fossil fuels. Additionally, climate change threatens to reduce the state’s water supply, and higher temperatures result in evaporative water loss from the state’s reservoirs and streams. All of these factors place additional pressure on fish and other wildlife, which rely on consistent flows of clean water for their existence. While modern water users in Colorado employ the state’s streams for diverse purposes, they are still confronted with the same limits and challenges of aridity faced by nineteenth-century settlers.