For the last 3,000 years, Tucson's waterways - including rivers, streams and creeks - ran freely much of the time and were a reliable source of water for everyday use and irrigation farming.
The beneficiaries of this plentiful water included the predecessors of the Hohokam, the Hohokam and their descendants, early Spanish, Mexican and American settlers, and finally Tucson residents.
But in the last 100 years that reliable water source has disappeared, leaving mostly dry streambeds.
What happened and how was Tucson's water resource renewed?
This is Part 1 of a two-part series to answer these questions.
The Santa Cruz River and the waterways that drain into it were the primary source of water for Tucson. Those waterways included Sabino Creek, out of the Santa Catalina Mountains; Agua Caliente Creek and Tanque Verde Creek, out of the Rincons; and Pantano Creek, fed from Agua Verde and Rincon Creeks, southeast of Tucson. These all flowed into the Rillito River, which in turn drained into the Santa Cruz River.
Cañada del Oro Creek, out of the Santa Catalinas, drained directly into the Santa Cruz River.
According to the book "Arizona's Changing Rivers: How People Have Affected the Rivers," the Santa Cruz River once was active all year round from its headwaters in the San Rafael Valley, southeast of Patagonia, south to Mexico, and then turning north to about Tubac, often as a series of marshes (cienegas), rather than a flowing river.
From Tubac the river went underground, surfaced near San Xavier del Bac mission, and from there alternated between being above ground and underground until surfacing at a dependable waterhole at the north end of the Tucson Mountains.
To the north, the river apparently "ended in the desert" before reaching the Gila River, except during floods. Springs between San Xavier and the Rillito River created marshes and added to the flow just west of Tucson.
In 1881, with Tucson's population at around 7,000, the Tucson Water Company began delivering piped water from the Santa Cruz River into town. Until 1887, Tucson residents could buy river water for a penny a gallon from vendors who transported it in bags draped over burros' backs.
After that water was sold by the bucket or barrel and delivered door-to-door in wagons.
The decline of the Santa Cruz River as a water source for Tucson began in 1887. Samuel Hughes (prominent in the incorporation of the city of Tucson and establishment of public education) attempted to increase the water supply to his fields north of St. Mary's Road. Interfering with an existing network of irrigation canals, he built a new, deep ditch to tap the subsurface flow of the river.
Large floods during the next four years caused the ditch and others to rapidly erode, both downward and laterally. Gravity irrigation with surface water was no longer possible. However, by using wells to draw water from underground river flow and cement-lined canals, agriculture continued in the Tucson urban area.
Irrigation farming was also conducted along the Rillito River at places like the Mormon settlement of Binghampton and at Old Fort Lowell.
Thankfully, there was another source of water besides rivers to provide for Tucson's growing needs - underground water.
Beneath the Tucson Valley, formed in the same basin and range geological events that created Tucson's mountain ranges and the subsequent erosion from those mountains, lies a tremendous mass of porous sediments filled with water deposited during long-ago glacial periods and over thousands of years from seepage of rain and snowmelt runoff.
This body of water-filled sediments (aquifer) extends from very near the surface of the Tucson Valley in some places, down to 1,200 feet deep. In the 1890s it probably contained an incredible 20-"plus" cubic miles of water.
Tucson began pumping that groundwater in the 1890s when the Tucson Water Company built 20-foot deep wells all over the Tucson metropolitan area. As more and more water was pumped out of the ground, the underground flow of the Santa Cruz and Rillito Rivers essentially "dried up," bringing an end to irrigation farming along the rivers by the 1930s.
In 1940, with Tucson's population having grown to nearly 37,000, Tucson began increasing its groundwater pumping and for decades, groundwater was our only water source. We pumped groundwater faster than nature could replace it (with natural recharge from rain and snowmelt), causing the water table in some places to drop more than 200 feet. Groundwater pumping also caused the land in some places to sink and drew off water from riparian areas.
By 1970 Tucson's population had exploded to more than 260,000 people. Unless we wanted to mine underground water down to the last drop, something else had to be done!
Next week: Tucson's Waterworld, Part 2
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