August 20, 2023 – In 1868 Phillip Duppa predicted that from an obscure settlement in the Salt River Valley “a new city will spring phoenix-like upon the ruins of a former civilization.” Duppa was, of course, referring to what is now known as Phoenix, Arizona, and he is credited with giving it its name. No longer an obscure settlement in the Sonoran Desert, Phoenix is the heart of the fifth largest metropolitan area in the United States.
Duppa and other early settlers like him recognized the potential of the area: the Salt River, if its floods and droughts could be managed, could provide the water necessary for growth and prosperity. Duppa’s prediction was based on the observation that a previous civilization, the people of the Hohokam culture, had once thrived in the area by virtue of the massive irrigation system they designed and constructed thousands of years before the arrival of Europeans.
Yet, the growth and prosperity associated with the valley’s urban development has come with a significant cost to its natural environment. One must look no further than the portion of river stretching from the Granite Reef Diversion Dam to the Gila River: except for Tempe Town Lake, it is mostly a dry riverbed.
Where once the Salt was reported to have flowed 200 feet wide and 4 feet deep, today it is a dry, barren riverbed except during the spring runoff and the summer monsoons. Similarly, the path of the Salt through the valley has been drastically altered from its original meandering, braided course. Today it is essentially a straight ditch that is contained within the cement and rock levees that comprise its banks.
The modern changes to the river valley have resulted in drastic changes to the ecosystem, too. Gone is the historical riparian zone with its stands of cottonwood and willow, replaced with the invasive salt cedar (tamarisk) that was introduced in the 19th century. Gone too are the bonytail chub, Colorado River pikeminnow, and other native fishes.
Tempe Town Lake is another story altogether. It is a two-mile long artificial reservoir that was created by damming the dry Salt River and adding water. Ironically, the added water comes not from the Salt River but from the Colorado River 200 miles away across the Sonoran Desert via the Central Arizona Project system of aqueducts, tunnels, and pumping stations. According to the Arizona Municipal Water Users’ Association, approximately 2,000 acre-feet of the lake’s water is lost annually to evaporation – approximately equal to the water usage of four golf courses. The losses must be continuously replenished to maintain a constant water level.
Further upstream where the Salt River Project (SRP) dams and reservoirs are located, there are other costs to the natural environment. The dams have flooded the historical riparian zones, leaving only steep, rocky shorelines in their place. The water levels in the reservoirs fluctuate due to the demands of irrigation and hydroelectricity generation, precluding the establishment of new riparian zones along the shores, although invasive salt cedar is established here, too.
Therefore, endangered and threatened species such as the southwestern willow flycatcher, the Yuma clapper rail, and the yellow-billed cuckoo have lost much of their vital habitat. Likewise, many native fish are gone and have been replaced by non-native bass, bluegill, and trout planted from hatcheries by the Arizona Department of Game and Fish.
Above the dams and reservoirs, the Salt River still flows much as it always has through its deep, red canyon. But even here the natural environment has been touched by human development. A primitive road lines a portion of the canyon bottom, and a highway bridge crosses its waters. Detritus from abandoned asbestos and salt mines fans out from shafts in the canyon walls. Salt cedar clogs the river bottom. Less than 50 miles of river is now protected in the Salt River Canyon Wilderness from further encroachment.
Phillip Duppa was correct in his prediction that a great new civilization would rise in the Salt River Valley. What he didn’t predict, or at least didn’t state, was that the new civilization would have a far-reaching negative impact on the river’s natural environment. Much has been gained. But much has been lost.