A year after Pima County cleared a big swath of the Rillito River of vegetation and excess soil as a flood-control measure, parts of the Pantano Wash recently got a similar treatment.
A vast expanse of the wash northwest of Tanque Verde Road now looks like a sandy beach.
“New soil cement bank protection has recently been installed for the Pantano Wash bank protection and river park project between Tanque Verde Road and Fort Lowell Park,” said Larry Robison, engineering division manager for the Pima County Regional Flood Control District.
“From our hydrologic modeling for the project, the vegetation was covering a sand bar that needed to be removed as the sand bar was constricting flood flows between Costco (a large store near the wash) and the Tanque Verde bridge” over the wash, Robison said. “The work involved building bank protection and removing vegetation.”
Vegetation that had grown in the channel, potentially restricting water flows, was mainly creosote bush, he said.
“Creosote bush is a native plant, but it’s more of a weed that grows like crazy,” he said.
“We’ve also selectively removed some of the invasive species like tamarisk and buffelgrass,” he said.
One part of the channel had been used as a commercial sand and gravel operation in the past.
“As such, the area contained numerous large pockets of subsurface materials varying from natural to man-made inert material, and also non-inert material — dumped cars, scrap metal” and other material, Robison said. “We used this project as an opportunity to clean up the entirety of that channel area to ensure no future issues with dumped material.”
The work, begun last year, is continuing this year with construction of a paved, 1.4-mile path along the wash for the river park system and planting of vegetation along the banks.
He said work on a wash segment southeast of Tanque Verde Road was done several years earlier and that vegetation in the channel has since regrown. It’s being left as it is for now, Robison said, but he noted that it will be inspected periodically for sediment buildup.
It’s likely that other watercourses will receive work for bank protection and flood control, too.
“The regional watercourses within the metro Tucson area do require occasional maintenance to restore the flood-carrying capacity of the watercourses,” Robison said. “The bank protection is designed to allow for some regrowth of vegetation. The extent of the maintenance depends on the amount of vegetation, sedimentation and the amount of adjacent development.”