On the surface, it's a road project - The Explorer: Pima Pinal

On the surface, it's a road project

Beneath, La Cañada a big drainage effort

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Posted: Tuesday, September 7, 2010 11:00 pm | Updated: 8:17 am, Thu Mar 24, 2011.

On the surface, reconstruction of La Cañada Road from Calle Concordia to Ina is a $13.2 million road improvement.

Beneath the surface, literally, it is an enormous drainage project.

This portion of the La Cañada project crosses five major washes, each one a little different from the next. There are 22 culverts, six of them major. Of the total project cost, "one third of the project cost-wise is directly attributable to drainage," according to Rick Ellis, engineering division manager for the Pima County Department of Transportation.

"What people see and feel and experience as a new roadway is only a small part of what it costs," Ellis said. "It's about moving water."

"It's ironic, we live in the desert, and we do all this work to move water," said Ed Anderson, project manager for contractor KE&G Construction.

Before this project, La Cañada was a two-lane, rural roadway with largely "dip" wash crossings and no "deep" drainage work other than at Hardy Road. The major Carmack Wash was "hugely wide," Ellis said.

"We are taking this whole neighborhood out of the flood plain. … We're taking a massive water way, trying to … control it, and still not ruin everything" around it, Ellis said.

The Carmack Wash structure has been built to accommodate "the 100-year event" in terms of flow. That event is estimated at 3,122 cubic feet of water per second, a figure Mike Bertram, transportation section manager for HDR Engineering, pulls instantly from memory. A cubic foot per second is "about the size of a basketball," Bertram said.

"We model a 100-year event," Ellis said. "It's unlikely people have seen that. We're looking worst-case scenario."

A seven-cell box is in place at Carmack. Each cell is 10 feet wide and five feet high, concrete on all four sides. The floor of each cell is 16 inches thick. All of the concrete is being poured. KE&G Construction could have placed precast concrete if it chose. "You can build it cheaper than we can buy it premade and set," Anderson said.

The Carmack Wash structure is on a skew, because the wash crossing is not perpendicular to the roadway. "We had to twist the box," Bertram explains.

It is built to gather and concentrate water on the upstream east side.

"We're reaching out and grabbing the water," which is typically flowing in a sheet, Bertram said. Water is concentrated and sped up closer to the roadway, so engineers can "pop it through the box" beneath the roadway, then spread it, "slow it down and let the surface elevation come back out" beyond the roadway, Bertram said. The wash turns a corner, then is fanned and slowed so the observer "never would have known it went under the road in a box culvert," Bertram said.

Below the Carmack Wash crossing, KE&G has excavated hundreds of yards of material to a point 650 feet beyond the roadway. It's a big scrape of material.

"We're chasing the grade until it reaches existing grade," Ellis said.

Immediately below the structure, crews are placing "D50" rocks, on average 12-inch rocks buried in concrete. This "grouted rip-rap" is intended to slow the water.

"Velocities are so high, and we're fighting the curve," Bertram explained. Tilted concrete pads, gradually flattening over distance, further protect the banks and help slow and contain the water.

"We generally build the outlet side first," Anderson said. "It has to be able to receive flows during construction season."

The rain is "not our friend," said Anderson, who enjoys the monsoon and rainy season personally, but loathes it professionally.

A major monsoonal rain did wash out work at the Nannini Wash drainage. "We were in the process of building it" when heavy flows hit, leaving behind two feet of sand, Anderson said. "We had to dig it out, reset the forms, reset the rebar. We had to untie the rebar to pull it out to get the sand out." Sand was excavated by hand.

"It took three days of extra work," Anderson said. "We are on schedule right now."

Nannini Wash, just south of Ina, previously had structures in place to move water below the roadway. One other "cell," precast and set in this instance, has been added. The entire structure is being extended to allow crossing of four lanes, rather than two.

Peglar Wash has boxes 10-by-seven feet. It too, has "a good flow to it as well," and the 100-year event is estimated at 2,633 cfs, Bertram said.

A total of 500 feet of mortared rip-rap is being placed on the outlet side of Peglar. It will eventually fill with dirt, and appear "not as engineered" as it will for a while. "We expect a lot of sediment," Ellis said.

Smaller drainages require pipe installation. Catch basins and the major structures are more expensive, and take longer to build.

Utility relocations on La Cañada have overlapped with construction

Utility relocations have been a challenge of the La Cañada road construction project.

Typically, lines are moved before major road work begins. Why? "Any excavation work is in conflict with any sub-surface utilities," said Mike Bertram, transportation section manager for HDR Engineering, the company that has designed the engineering work.

On La Cañada between Calle Concordia and Ina, a number of utilities must relocate lines, among them Tucson Electric Power, Qwest, Southwest Gas, Metro Water, Comcast, the Western Area Power Administration and Mesa Land and Water, a private water utility.

"We're continually pushing the utilities to meet our challenges," said Rick Ellis, engineering division manager for the Pima County Department of Transportation. "Ideally," they're done "before construction. In reality, there's an overlap we've had to manage through."

Clearing and "grubbing" of the surface typically follows utility relocation. The project had "a significant salvage operation," Anderson said, with more than 1,000 trees, cacti and shrubs going to the Pima County Nursery facility. That work took two months.

The project is generally on schedule, working through preliminary construction and activity as well as rain delays from last winter and the current monsoon.

"They've caught up and done a really good job," Bertram said of general contractor KE&G Construction. "They definitely earn their money."

No more dips

When it's done, La Cañada between Calle Concordia and Ina won't have the dip crossings that have drained storm water since its construction.

Dip crossings slow traffic, increase maintenance costs and are problematic for speeding emergency vehicles.

With the work, La Cañada should be safer, faster and less congested, officials say.

© 2014 The Explorer. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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