Cherry Field, northwest of South Kino Parkway and Aviation Highway, will soon be a 17.7-acre, 20-feet-deep hole in the ground.
Fleets of dump trucks, bulldozers and front-end loaders are scooping out a basin where Tucson Unified School District playing fields once stood.
The two baseball fields and soccer and football practice areas will be replaced once the area is lowered about 20 feet. It will then serve as a place for water to flow when Arroyo Chico floods.
Cherry Field is the first of four detention basins being built in the second phase of the Arroyo Chico Multi-Use Project, designed to end the flooding of the arroyo along a six-mile stretch from Alvernon Way to where it enters the Santa Cruz River near St. Mary's Road.
Arroyo Chico drains 11.4 square miles of central Tucson.
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Parts of it, also known as Tucson Arroyo, run underground in huge cement culverts through some of the city's densest neighborhoods and under some of its busiest streets.
At $17 million, the Cherry Field basin is the largest and most expensive detention basin being built as part of the U.S. Army Corps of Engineers project, said Suzanne Shields, director of the Pima County Regional Flood Control District.
It's part of the larger Arroyo Chico Multi-Use Project, a joint undertaking of the city of Tucson, Pima County and the Corps of Engineers. It began with detention basins at the city's Dell Ulrich Golf Course, formerly Randolph South, completed in 1996.
Shields said the series of basins at Dell Ulrich worked well during the July monsoon storms that flooded parts of Midtown and Downtown. "Those basins took in 3,400 cubic feet per second and knocked it down to 269 cubic feet per second," she said.
Downtown still flooded, but it would have been much worse, she said.
"The old storm-drain system under Fourth Avenue just can't handle the flow," Shields said. "The goal is to take a normal flash flood, hold it back and let it drain out in 30 hours."
Ultimately, the project will remove 1,100 homes and businesses from the outlines of the 100-year flood plain, according to project documents.
It will also remove about 140,000 cubic yards of soil from Cherry Field.
The first loads of dirt went to the city's Rio Nuevo site, where it will be used to lift part of the Downtown redevelopment area above the flood plain and to fill in an old landfill that is being excavated there.
"It's really great for the project," said Bill O'Malley, Rio Nuevo's construction manager. "We're essentially getting free fill."
This week, trucks began hauling Cherry Field's dirt to an East Side landfill that the city is closing and needs to cover.
The excavation is being done by Granite Construction Co.
