Excessive use of water in the Rio Grande Basin for irrigation and surface water has led to many economic and environmental challenges. The principal source of water for irrigation in the San Luis Valley between 1880 and 1950 was surface water. A large network of canals was built from 1880-1890 to irrigate lands in the eastern and central parts of the closed basin, including those fed by artesian wells and springs. The first drilled artesian well in the valley occurred in 1887 and within 10 years, more than 3,000 wells existed . By 1915 most of the area around Mosca and Hooper became waterlogged because of this irrigation. Drainage systems constructed between 1911 and 1921 to reclaim waterlogged lands alleviated some of the problems but created waterlogging in areas downslope.
Waterlogging causes soils to become alkaline (pH higher than 8.5), and groundwater has become highly mineralized from concentration of salts. Where salts are allowed to build up, the fertility of the soils is decreased. Excess water must be used on the fields to break up the salt and carry it back below the ground level. Pumping large volumes of water over long periods of time also uses a tremendous amount of energy. Since energy prices fluctuate, a farmer may find it difficult to judge energy costs, which is a major factor in the overall production of a crop.
By the 1880s water conflicts were occurring and the need arose to adjudicate water rights. In 1888, a General Adjudication of water rights occurred with supplements being added over the years. In addition to these adjudications, a severe drought hit the valley and other areas in 1893. This resulted in bank failures, farmers leaving the valley, the disappearance of some small communities, and the Rio Grande drying up along the Texas-Mexico border.
Eventually, the Rio Grande Compact was signed in 1938 by Colorado, New Mexico, and Texas, to equitably apportion the waters of the Rio Grande Basin. Because too much water was being taken from the Rio Grande by the valley for agricultural development and not enough was being sent downstream, Colorado had to find a means to transfer more water downstream to New Mexico, Texas, and Mexico. Initially envisioned in the 1930s, the Closed Basin Project did not get started until the 1980s. Under this project, 170 wells now tap water from the unconfined aquifer and pump 100,000 acre-feet of water per year into an aqueduct that transfers the water to the Rio Grande for use downstream.
Historically, depth to water in the unconfined aquifer had been less than 12 feet below ground surface. However, extensive irrigation in the valley using groundwater wells has resulted in depletion of the aquifer. In the period 1969 to 1980 water level declines of up to 40 feet were documented in the unconfined aquifer. Since 1976, Colorado’s Water Division engineer estimates that the unconfined aquifer has lost 1 million acre-feet of storage.
Depletion of groundwater resources in the valley spurred the Colorado legislature to adopt legislation requiring the State Engineer to promulgate new rules on future appropriations from the deeper, artesian confined aquifer. These appropriations now require an augmentation plan.