History of Tres Rios

Salt River Flooding Creates a Need for Flood Control Solutions

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The Salt River runs 200 miles from the White Mountains in eastern Arizona to the Gila River. Despite the dry appearance you see today, it was a source of frequent flooding and loss of property.

Why was Tres Rios Constructed?

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1. Flood Control
   
2. Habitat Restoration
   
3. Recreation and Environmental Education
   

In the Beginning - How was Tres Rios Constructed

In the mid-1990s, Water Services management explored the idea of a wetlands project to assist in the final phase of the wastewater treatment process as a means to reduce the cost normally associated with traditional methods, but while still following Clean Water Act rules.  The testing phase of the wetlands process required the construction of test cells (see photo below) that proved the concept worked. Several larger test wetlands were then created closer to the river bottom on the east side of 91st Avenue. The success of those tests led to the next phase involving numerous stakeholders and a much larger goal. 

The Path to Full-Scale Wetlands

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In 2000, the U.S. Army Corps of Engineers (ACOE) received approval from Congress for the Tres Rios Ecosystem Restoration and Flood Control Project. The City of Phoenix partnered with the ACOE to improve and enhance a seven-mile long, almost 700-acre section along the Salt and Gila Rivers in southwestern Phoenix. The project received 65 percent of the funding from the ACOE, with 35 percent coming from the local sponsor, the City of Phoenix and the Sub-Regional Operating Group Members (Scottsdale, Tempe, Glendale, and Mesa). Technical and financial assistance was also provided by the Flood Control District of Maricopa County. Construction lasted from 2007 – 2012.

Wetlands in the Desert?

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Former agricultural fields were graded and contoured into the wetlands you see today. Once the depths were just right, plants including rushes, sedges, arrowhead, cattail, and floating aquatics were installed to recreate wetlands of the southwestern United States.   

Restoring Riparian Habitat

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Most of the rivers in the southwestern United States have become choked with a non-native plant, salt cedar, or tamarisk. This plant was originally brought into this country in the 1800s as an ornamental plant, and for stream bank stabilization. In the 20th century, staff started to realize the danger of importing foreign plants into the fragile desert environment. Sonoran Desert wildlife has lived with native plants for millions of years.

The plant and animal communities have evolved together, with the animals using the plants for shelter and food, and the plants using the animals for seed dispersal. Native plants are perfectly suited to sustain native animal populations. Now, the salt cedar has displaced many of the native plants. The salt cedar invasions have thrown off the natural balance between plants and animals, making survival more difficult for the native wildlife.

To reverse the process, Tres Rios staff removed large tracts of salt cedar and replaced it with native cottonwood/willow riparian corridors. In some areas, where the salt cedar is very thick and will be impossible to replace, the river sediment will be dug down and filled with water. This will prevent regrowth of the salt cedar, provide habitat for waterfowl, and offer a clearer channel for flood flows to utilize.