The agricultural fields of the San Luis Valley are irrigated in two ways: gravity-flow surface ditches, also known as acequias, and mechanized circle pivot irrigation. Acequias were the historic means of irrigation. Acequias, which are community-operated canal systems that carry snow runoff or river water to distant fields, evolved over 10,000 years in the deserts of the Middle East and were introduced into southern Spain by the Moors during their nearly 800-year occupation. Spanish colonizers took acequias to the New World where they were blended with similar irrigation systems of the Native Americans. Acequias include specific governance over water distribution, water scarcity plans, and all other matters pertaining to what is viewed as a communal resource. The mayordomo, or watermaster, of the acequia makes decisions about water distribution among community members, with the consent and advice of the acequia members. Each member has one vote, and so each member is an equal in the decision-making process. The farmers around the town of San Luis and surrounding villages own their irrigation water in common, following the acequia system established by these early Culebra River communities. Each ditch company holds regular meetings, elects a board, and designates a mayordomo to administer the system.
The first acequia was the San Luis People’s Ditch, which was dug in 1851. Being the oldest in the valley, the People’s Ditch also holds the first adjudicated water rights in the state of Colorado. Currently it irrigates approximately 2,100 acres of hay and other row crops. A majority of parciantes, or stakeholders, are descendants of the original founders of the acequia.
Within the heritage area, there are approximately 130 named gravity-flow irrigation ditches comprising approximately 1,300 miles of irrigation channel. While most of these ditches divert water from rivers and streams, others channel water directly from flowing artesian wells and springs.
The longest and most complex irrigation system in the San Luis Valley is the Rio Grande Canal, which began construction in 1881. While most of its 210 miles of canals and laterals provide water to Rio Grande and Saguache counties, many miles of this system also irrigate western Alamosa County. Completed in 1884, the canal’s main channel is 60 feet wide at the bottom, 90 feet wide at the top, five feet deep at the sides, and six feet deep in the middle. Today, 31 prior appropriations take 1,699 cubic feet per second of water from the canal. In an average year, 30 percent of the Rio Grande’s water is diverted into this canal system.
Mechanized center pivot irrigation, which was introduced to the valley in the 1950s, began to tap the tremendous amount of water available in the confined aquifers. While the aquifers had been tapped as early as the late 1800s through drilled artesian wells to provide surface flow to ditches, the center pivot irrigation system provided a much more efficient method of distributing the water. This system is based on a well being dug in the center of a field and an irrigation pipe mounted on wheels gradually moving around the well. This arrangement forms circular field patterns. Most of the center pivot systems are found in the northwest portion of the valley, mainly in Saguache, Rio Grande, and Alamosa counties. These counties were organized under the Public Land Survey system with the basic land parcel being the quarter section, 160 acres. Since the initial center pivot systems were designed chiefly for quarter section land parcels on the Great Plains, it was relatively easy to apply the technology to similar areas under the Public Land Survey system.