Most construction projects involve stripping away trees, plants, and soil to make room for concrete. But at the land bridge joining the two halves of Phil Hardberger Park, construction seems to be moving in reverse.
On Friday, SpawGlass crews unloaded truckloads of soil on top of the concrete bridge that now spans Wurzbach Parkway. Some workers planted trees, while others installed foundations for the 8-foot weathered steel walls that will in a few months make the bridge feel like an enclosed corridor of native habitat, complete with walking trails.
The bridge will join two halves of the 330-acre park on San Antonio’s North Side currently separated by a busy thoroughfare. On Dec. 11, the Phil Hardberger Park Conservancy plans to celebrate the completion of the project a decade in the making.
“I want [people] to come and love it,” said former San Antonio mayor Phil Hardberger in a Friday interview. “I want them to be proud of it, and I want them to feel a sense of ownership that this is theirs – not just the neighbors around it, but the entire city of San Antonio.”
Denise Gross, the conservancy’s director, said the timing of the bridge’s completion is perfect, with visitors to the park increasing during the coronavirus pandemic. Shutdowns and social distancing have led U.S. residents outdoors at historic rates.
“We’ve always known that nature provides a refuge, and lots of people are discovering that,” Gross said.
The 150-foot-wide crossing will be the first of its kind in the U.S., designed for people and animals to cross the four-lane road below. The nearest similar bridge is a set of overpasses in Banff National Park in Canada meant exclusively for critter crossings.
The striking design for San Antonio’s land bridge came at a steeper cost than a simple pedestrian walkway. Of the $23 million in needed funds, $10 million came from private donations, and the remaining $13 million came from the City’s most recent bond that voters approved in 2017. The project proved the most controversial included in that bond, with many questioning the bridge’s price tag and whether wildlife would actually use it.
Hardberger said that San Antonio deserves such public landmarks that add beauty to the city and improve outdoor access.
“I think it will also become an iconic park for San Antonio, just like the Alamo and the San Antonio River, one of those things that people will be proud of and talk about, just like they do the silver bean in Chicago,” Hardberger said.
The land bridge reaches 25 feet tall at its high point and is made of concrete, with a layer of polystyrene foam blocks used to reduce weight compared to soil. Over that base, crews have sculpted trucked in and sculpted contours of soil, ready for planting grass, wildflowers, shrubs, and 725 trees.
All the topsoil comes from the park itself, with plants selected from a list of those already found growing there, according to Danny Watson, landscape architect and principal with Rialto Studios, which designed the project along with Stimson Studio and engineering firm Arup.
“There’s different seed mixes for different areas,” Watson said on a tour of the site Friday. “There will be other areas that won’t have any big trees, it’ll be more open and less dense. … We don’t want this to ever look constructed. We want it to look like Wurzbach was tunneled underneath.”
The 8- to 10-foot-wide trail will hug the bridge’s eastern side. Made of a decomposed granite and crushed stone paving material and with grades at 5 percent or less, the whole trail will be ADA-compliant, designers said. A 6-foot-wide metal skywalk on the park’s east side will cut through the upper story of forest and join with the trail near the top of the bridge.
With walls on either side, those crossing the bridge won’t be able to see traffic, Watson said. That’s also necessary for prevent wildlife from leaping off the bridge.
“It’s also a safety issue because we can’t get deer up here and then let them jump over,” Watson said. “It’d be kind of counterproductive.”
Animals looking for a safe way to cross Wurzbach will find their way to and across the bridge, said Christine Westerman, an ecologist with SWCA Environmental Consultants.
“They’re going to be going along and they’re going to see the vegetation continuing here and if they feel comfortable with the amount of shelter and cover they have, they’re going to keep going,” Westerman said.
On each end, the finished bridge will include a different viewing blind designed by local artists Cade Bradshaw and Ashley Mireles. The blind on the east side looks out on a water feature meant to attract wildlife, while the blind on the west will be near a 250,000-gallon underground rainwater catchment system that will supply water for irrigation.
A few seasons will pass before the plants fully establish themselves, designers said. But eventually, according to Westerman, nature will take over.
“Once they get the trees in, then birds are going to come in, and they’re going to drop seeds,” Westerman said. “There’s going to be this process of succession where more and more species are going to come in on their own. The ones that are most successful are going to reseed the most, so the best-adapted plants are going to spread in particular areas, just as if it were a native prairie restoration.”