Redirecting the river: Researchers, officials plan sediment removal for the Santa Cruz

TUCSON, Ariz. (KOLD News 13) - Just under a year ago, Tucson Water launched the Santa Cruz River Heritage Project, an undertaking that brought much fanfare when city officials opened the valve to provide year-round water flow to a dried-up section of the river at the base of A Mountain.

Since then, lush, green vegetation, along with an abundance of wildlife, made its way back to the Santa Cruz, which is now a bird watcher’s paradise.

But that’s all about to change after city officials drastically cut down the water flow this week.

“I keep telling people this is like a big science fair project for us, trying to figure out how the river responds to the water we’re putting in there,” said Fernando Molina, a spokesperson for Tucson Water.

Since June 2019, the results of that perennial water flow have been astounding, surpassing the expectations of local researcher Michael Bogan.

Bogan, an aquatics biologist and assistant professor at the University of Arizona, documents all the new species bringing life back to the Santa Cruz.

“I’ve been gathering a lot of information with my students over the last year and we’ve seen the ecosystem develop," he said. "We’ve seen the recovery and so that information can be useful for people that are trying to manage the flood control and manage the water levels, things like that.”

Several government agencies turn to Bogan’s expertise for guidance on how to move forward with city plans.

“I’m an accidental expert,” Bogan said. “It’s really rewarding because normally, as a scientist, we publish papers in a bunch of jargon that nobody understands, in a scientific journal nobody reads, and it probably never gets used. Whereas here, that information we’re collecting is being used immediately to enhance the ecosystem as we do the flood control activity.”

All of that research is paying off, as the Pima County Flood District uses it to bulldoze this sensitive area.

“The reason that we need to do this is that the sediment is in the channel and it prevents floodwater, when a flood comes, from staying in the channel,” said Eric Shepp with the Pima County Flood Control District. “We determined that many hundreds of homes and businesses were in harm’s way because of the sediment in the river.”

It's a massive undertaking.

Shepp said crews will remove 85,000 cubic yards of sediment, digging down 5 to 10 feet, and hauling it all off to the nearby A Mountain landfill, an old dumpsite used from 1953 to 1962.

“The small hill that we’re going to make is about 4 to 5 acres in size and about 10 to 13 feet high,” he said.

It’s a balancing act of creating a manmade flood channel while keeping as much of the new vegetation and wildlife habitat intact.

“Because this is an accidental wetland, we don’t really know what the topography is like in here in this sediment that’s been deposited,” Bogan said. “And, so, if we remove the sediment that’s right here, right now, the water is just going to dive in that river channel and the wetlands is going to dry up."

In order to prevent that from happening, Bogan is surveying the riverbed to re-channel the reclaimed water.

“We want it to flow that way and create and extend the marsh in this area, the preservation area, but we need to see how much sediment we’re going to have to remove to create a little channel so that the water will actually flow that way,” he said.

To get the project started, and to give contractors a safe place to work, Tucson Water cut back on the water flow from 1,000 gallons per minute down to 250 gallons.

Now, there’s one big question left: Will it work?

“There’s always a concern, rivers have a history of doing what they want to and not what people want them to do,” Bogan said.

But, Molina said, with proper water flow management, and the resiliency of nature, the project should accomplish both goals of flood mitigation and preserving this living watershed.

“It will recover and recover quickly and in the long run it’ll be much better and much healthier for the channel and the environment we’re creating out there," Molina said.

Now that the water flow has been scaled back, crews with heavy equipment will make their way to the site within the next week or two. It will take crews two to three months to remove all the sediment, which is expected to cost around $500,000. This is the third and final section of a sediment removal project that cleaned up other parts of the Santa Cruz.

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