Mule deer have been given two 12-foot high, 20-foot wide, 172-foot long culverts so they can cross beneath the new Twin Peaks Road, helping the animals find their way along the fan of the Tortolita Mountains.
The Regional Transportation Authority is providing $780,659 for wildlife enhancements on the roadway. That sum helps pay for the major deer crossing ($595,844, to include larger culverts, related materials and construction, additional fill material, added right-of-way and design expenses), three 19-by-30-inch culverts below the four-lane roadway to further assist smaller animals ($51,315), fencing along the roadway that is intended to keep wildlife off, as well as “funnel” fencing that directs larger animals toward major crossings ($105,496), and post-construction monitoring to include game tracking and field verification to see what animals are crossing where ($28,500).
Twin Peaks Road crosses the Tortolita Mountain alluvial fan, a critical area for wildlife.
“When you build a new road, you cut off their ability to get anywhere else,” said Jennifer Christelman, environmental engineering division manager for the Town of Marana.
Populations become isolated from one another. Without connectivity and safe passage, “you’re not mixing gene pools,” she said. “It’s the genetics that are a problem, for all the species.”
Marana worked with Pima County, the RTA and the Arizona Game and Fish Department to survey the entire Twin Peaks project, both existing and undeveloped sections of roadway. A 2006 Game and Fish study determined road kill numbers, track and scat counts and “hot spot” locations, Christelman said, yielding “some good information.” During a survey period, 16 identified mule deer “hits” were identified in two specific locations.
When it comes to road crossings, deer are a different sort of species than coyotes and javelina, for example. Deer need head room. They need “that sense of security” regarding culvert height, width and length. Sight distance is important; a deer won’t enter a culvert if it can’t see its way out, Christelman said.
Engineers use an “openness index,” multiplying the height and width of a culvert, then dividing that figure by its length, to measure the practical usefulness of a wildlife crossing. An openness index of .75 is recommended by the Arizona Game and Fish Department for deer; each of the side-by-side Twin Peaks culverts, with eight feet of height clearance, exceeds the openness index requirements.
To accommodate the larger culverts, Twin Peaks Road rises subtly south of the mule deer crossing, and descends slowly north of it. “We had to bring in a large amount of fill to get the culvert height for the mule deer,” said Christelman, and RTA helped with some of that cost.
The Town of Marana paid for the culvert size that would have been sufficient to accommodate high water. RTA paid the difference for the larger, wider culverts to accommodate deer. Adjacent zoning restricts disturbance to 30 percent of large lots, leaving open space for animals and making this “the perfect location” for larger wildlife crossings, Christelman said.
When the fencing is in place, “we’ll figure out what’s using it, how often, and try to figure out their patterns,” Christelman said. “It’s a new science. New, good data is coming out.”
Marana plans to place game cameras in the two major culverts “to see what types of things are using them,” Christelman said. “The first year or so,” she said, deer “will be afraid to use it.”
Thirty-two crossings were needed along the new roadway for drainage. Most of them are useful to small amphibians and reptiles. While they are “of no use to any water drainage,” the three funded, additional crossings fill in spaces between drainage culverts that were more than 200 feet apart, too far for smaller mammals, reptiles and amphibians with shorter ranges, Christelman said.
Several culverts and crossings are of adequate size and spacing to accommodate medium and larger mammals such as bobcats, javelina and coyotes. “The only species we didn’t accommodate strictly because of drainage” was the mule deer, Christelman said.
The voter-approved RTA plan includes funds for wildlife crossings and enhancements to ease the impact of new transportation corridors and road improvements upon animals.
Many desert plants back to Twin Peaks Road landscape
Cacti and trees along the new Twin Peaks Road were harvested from the site by a cactus rescue group, the Arizona Sonoran Desert Museum and project workers.
Many were placed in a nursery during construction, then replanted along the roadway that opens to the public this Friday, Nov. 19.
“All of our landscaping came from the project, and we’re putting it back in the project,” said Jennifer Christelman, the Town of Marana’s environmental engineering division manager.
The 1.5-mile portion of Twin Peaks Road that newly crosses the Sonoran Desert parallels an old Jeep road south of Tangerine Road. Before a swath of desert was cleared, volunteers with the Tucson Cactus and Succulent Society came onto the section, rescuing 250 smaller cacti and succulents. People associated with the Arizona Sonoran Desert Museum came to the site and harvested 70 cacti, “primarily saguaro,” and in particular plants less than 4 feet high, Christelman said.
A majority of harvested palo verde, mesquite and ironwood trees survived temporary displacement, and have been placed between Linda Vista Boulevard and Tangerine Road. “The trees did great,” Christelman said.
During a drive on the new road, Town of Marana construction division manager Morris Reyna pointed to mature ironwoods and other trees that give Twin Peaks Road an established appearance. Before the opening, saguaros and other cacti were being placed in medians and within the right-of-way near the road, recreational path and sidewalk footprints.
There was a crestate or “crested” saguaro on the project. A number of saguaros remained in the nursery just before opening, along with a large number of barrel cactus.
“We’re curious to see how well they dealt with that stress period,” Christelman said. And it may take time to determine a survival rate.
Twin Peaks Road, Linda Vista to Tangerine
That includes construction and project management with contractor at-risk Borderland Construction ($24.9 million), land acquisition and rights of way ($3.6 million) planning, design and environmental work ($1.85 million) and water line construction, ($1.1 million).
Project partners are the Regional Transportation Authority, the state of Arizona and Pima County. The Town of Marana sold bonds for project funding.