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Sheesh, Caliche! 

Southern Arizona's pesky geological traits force changes in the Arroyo Chico flood-control project

A few things in Tucson are givens: It is blast-furnace hot in the summer. The UA football team won't play in the Rose Bowl.

And caliche in the soil is a real pain for everybody.

That last Tucson certainty is causing problems at three large flood-control detention basins being dug along downtown's Arroyo Chico, south of Broadway Boulevard.

"We knew there was some (caliche)," confirms Suzanne Shields, director of the Pima County Regional Flood Control District. But she says earlier boring done in the easternmost basin, No. 3, didn't fully reveal the caliche's 5-foot thickness, nor did it reveal how hard it is.

According to the Arizona Cooperative Extension, caliche is "a layer of soil in which the soil particles have been cemented together by lime."

In February, the caliche's extent slowed excavation on basin No. 3, the first of three deep holes slated to be excavated. Even now, the caliche can be seen among the earthmovers, trucks and bulldozers rumbling slowly through the basins under construction—a wide ribbon of stark white amidst the earth-tone hues of the soil above and below it.

Shields adds of the caliche: "We didn't run into this on Cherry Field." That project, just east of the three basins, was an earlier phase of the lengthy Arroyo Chico project.

The current $11 million phase began in October 2010 and is expected to be completed by the end of this year. While the three basins will help control flooding—presuming it ever rains again—the project was also intended to restore and enhance the natural environment found along the urban wash.

Almost seven years ago, a city official involved with the project said of the revegetation effort: "To a passer-by, it will look like a lot of native plants with more density than usual. ... In some thickets, it won't be comfortable to walk through." (See "Water Worries," Nov. 25, 2004.)

That certainly is the impression given by Pima County publicity material for the current project. A handout states that when the basins are completed, they will include "a combination of native riparian and upland species."

Because of the caliche issues, though, those plans may change. Shields indicates the mapping of the caliche in basin No. 2 should be finished this week, and will show just how deep and wide it is there.

"Then we'll make a decision on what to do for re-vegetation," she says. "We may stick to the original plan or create a cienaga (environment) by putting in native grasses. ... It's still our intention to do the re-vegetation, but (the caliche) may impact where and what we plant."

Shields says the cienaga concept would involve placing trees along the wash, as well as native grasses and marshy areas that would develop after a storm. This, she indicates, could attract birds to the area.

"We'd try to make the habitat similar to what was there before," Shields says of possible revisions. "We were going to change the plans anyway, because over time, we've found what works better with restoration projects."

The possibility of changing the planting plans doesn't bother Bill Richards of the Miles Neighborhood Association. The Miles Neighborhood is located on the north side of the arroyo.

"I like the idea," Richards says. "The basins are so huge, there's lots of room to plant all kinds of things."

Richards remembers an earlier concept called for creating small wetlands for birds, a proposal which was eventually dropped. "Maybe that can come back," he says.

His neighborhood, Richards points out, sees the project much differently than those living south of the wash. "We're looking at this as a public space and greenway which needs public amenities," he says.

Indeed, the potential planting changes don't sit well with Ted Warmbrand, vice president of the Barrio San Antonio Neighborhood Association; that neighborhood sits south of the basins. Warmbrand has been involved in planning for the project for years, and has often been critical of it.

When he first found out a few weeks ago that the planting plans may be altered, Warmbrand quickly sent the county an e-mail.

"Those plantings are not an acceptable option," he wrote of the potential changes. Referring to the initial concept, Warmbrand wrote that it was to have "significant replanting and 'open space' with lots of acceptable native vegetation in the area."

In a follow-up interview, Warmbrand says that his "feeling was we'd get open space and lots of native species. Grass was not a prominent part (of the plan). It doesn't seem like open space. It sounds like barren space with flowers and grasses that will grow when they grow ... (and) brown dirt other times."

Warmbrand also wonders how the possible planting changes might impact the wildlife formerly found along the wash.

"We loved hearing the frogs when the arroyo ran," he reminisces.

Part of the problem, Warmbrand argues, is the process that Pima County and the U.S. Army Corps of Engineers has used to keep people informed about the basins. Although there are monthly meetings, he says they're not really informative.

"Once things are in motion," Warmbrand says of construction, "they don't tell you what you need to hear. It's like pulling teeth (to get information)."

Warmbrand was scheduled to meet with county officials to discuss the project on Tuesday, June 7.

"I feel somewhat betrayed and disappointed on every score," Warmbrand says about the possible planting shift in the Arroyo Chico detention basin project.

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