Water Development, Extraction, and Diversion (page 2 of 6)

Pre-Settlement Water Use on the Colorado Plateau

In discussing the history of water use on the Colorado Plateau, it is important to differentiate between water conservation and water diversion. Agricultural methods employing water conservation include floodwater agriculture (farming on floodplains which become inundated by drainage), runoff agriculture (farming where mesa tops and/or other natural or manmade features divert rainwater to fields), and dry farming (reliance on direct rainfall). In contrast, water diversion is defined as the active capture and application of water, using dams, headgates, canal systems, and other such methods.

Water conservation and, in some instances, water diversion on the Colorado Plateau followed early agriculture, which began with the cultivation of maize. Current research suggests that maize was first domesticated in central Mexico about 3500 BC, and rapidly spread northward as maize farmers migrated into unoccupied floodplain niches. Archaeological evidence, in the form of 3,000 year old corn remains in the Four Corners region, confirms that late Archaic (500 BC to 1 AD) peoples raised maize to a limited extent. Peoples of the Basketmaker II tradition, a culture that existed from 1 to 500 AD across the Colorado Plateau and eventually gave rise to the Anasazi, were dependent to varying degrees on maize crops.

A modern check dam. Photo courtesy of Washington State Department of Transportation.

The earliest maize cultivation relied on various water conservation methods, not technically considered actual water diversion or irrigation. As mentioned, these methods included dry farming and floodplain farming. A widespread, but not likely common, form of water control throughout the prehistoric southwest was the construction of check dams. Check dams consist of a series of stone walls built across small ephemeral streams. Over time, each check dam would create a small field, as moist sediment built up behind the dam, allowing for prime cultivating conditions. Evidence of ancient check dams has been found across the Colorado Plateau, including Navajo Mountain, the upper Little Colorado Valley, Mesa Verde, and the Horse Flats of southeastern Utah.

Irrigation systems of the Chaco Canyon Anasazi

Water drainage canal at Chaco Canyon. Photo courtesy of National Park Service.

Non-irrigated types of agriculture remained vastly dominant throughout the Anasazi era (700-1200 A.D.), but as the culture flourished, irrigation and diversion systems were developed by some of the more advanced Anasazi groups. A look at some specific examples of large-scale Anasazi irrigation systems on the Colorado Plateau best illustrates the ingenuity and labor-intensive nature of these prehistoric undertakings. Remote sensing, particularly aerial photography and GIS, has been invaluable in determining the locations of ancient water diversion systems, as well as other agricultural features and road systems, all of which are large-scale land-use features not easily detected from the ground or with the naked eye. Chaco Canyon, the epicenter of Anasazi culture throughout the tenth to twelfth centuries, is characterized by one of the best examples of pre-Anglo water diversion systems.

The major waterway of Chaco Canyon, Chaco Wash, is a deeply entrenched and ephemeral source of water, rendering it virtually useless as an irrigation source. Instead, the Chaco agricultural system captured rainfall run-off from the mesa tops surrounding the canyon system, especially after heavy summer storms. The Chacoan system was not a passive one, in which fields were strategically placed below natural drainages, but was an active irrigation system, unique to the region. A large complex of diversion dams and canals with multiple headgates directed the water into extensive bordered grid fields on the canyon bottom. This advanced method of farming, and the large amount of land made arable because of it, is central to the  "Chaco Phenomenon," the rise of Chaco Canyon as the most complex and elaborate center of Anasazi culture. Chacoans were able to produce surpluses of food, allowing for the rapid technological and architectural advances that developed there, such as a widespread road system enabling trade among regional Anasazi groups.

Evidence suggests that these irrigation systems were constructed in the tenth or eleventh centuries and, over time, degraded the area’s soils. The high evaporation rate and alkaline nature of the soils of the arid San Juan Basin eventually caused salinization and nutrient depletion as a result of prolonged irrigation. Because of the degradation of the canyon’s soils, irrigation was largely abandoned toward the end of Anasazi occupation of Chaco Canyon, during the twelfth century, in favor of floodwater farming in outlying reaches of the canyons.

Other Pre-Settlement Water Use Systems

Mummy Lake, Mesa Verde National Park. Photo courtesy of National Park Service.

Another major Anasazi site, Mesa Verde, Colorado, had a different, but equally impressive large-scale water diversion system. Located at Far View Ruins, which were inhabited from 900 to 1100 AD, are the remains of an artificial reservoir called Mummy Lake, which is 90 feet in diameter and 12 feet deep. In its time, the stone-lined reservoir was capable of storing 500,000 gallons of water, which drained into terraced agricultural fields via a system of canals. An irrigation ditch originating from the reservoir extended approximately 4 miles in length. The ditch averaged 30 feet wide and 6 to 18 inches deep.

Other archaeological evidence suggests that prehistoric attempts to capture precious water were not only for agricultural purposes. Water was also needed for domestic uses—drinking, cooking, washing, and making pottery. For example, Wupatki National Monument in northern Arizona, once inhabited by the Sinagua people, contains at least four manmade water reservoirs, discovered largely by aerial photography. While it is highly unlikely that the reservoirs were maintained yearlong due to dry conditions, it is believed that the reservoirs were used to collect stormwater to be used for domestic purposes for periods of days or weeks, or as long as the water remained within the basins. Rain showers still fill these reservoirs today—at least one has been consistently used in modern times as a watering hole for local cattle.

The Hopi: Dry Farming Experts

Hopi cornfields at Moencopi. Image 2821a by Bill Belknap courtesy of Cline Library Special Collections, NAU.

The modern Hopi are believed to be the descendants of the ancient Puebloan cultures (namely the Anasazi) of the Colorado Plateau. Without doubt, the Hopi people have inhabited the Plateau for hundreds of years. Some of the garden terraces at Paaqavi (Bacavi) have been in use since approximately A.D. 1200. With generations of accumulated knowledge of the climate, soil, and hydrology of their home on the Hopi Mesas of their reservation, the Hopi are considered to be the among the best dry farmers in the world. By implementing a variety of agricultural methods, the Hopi ensure crop production during even the most variable years. These methods include dry farming in the washes or valleys between the mesas as well as gardening on irrigated terraces along the mesa walls below each village. At least 24 varieties of corn are planted, most of which are hybrids developed by the Hopi over many decades. By planting many varieties of corn in a land characterized by erratic, unpredictable rainfall and by spatially dispersing crop fields, food production increases dramatically. The Hopi cultural traditions and religious practices focus largely on agriculture and praying for rain and crop fertility. 

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Previous Page
Page 3 - Mormon Settlement and the Dawn of Large-Scale Irrigation on the Colorado Plateau
Page 4 - The Thirst of the Growing West
Page 5 - The Bureau of Reclamation Transforms the West
Page 6 - The Tide Turns
References