The University of Pennsylvania will begin construction today of its epic 24-acre Penn Park, the centerpiece of its 30-year master plan involving land it acquired from the U.S. Postal Service in 2004.

The $46 million riverfront development project on the eastern edge of campus will include athletic fields, tennis courts, bike trails, and a multilevel elevated walk. It will increase the urban university's green space by 20 percent.

Replacing bland asphalt lots and an old industrial site, the project will help to transform the landscape of West Philadelphia, and link the university's main campus with bustling Center City.

In short, it's trading ugly for pretty.

Construction is scheduled to be complete by mid- to late summer 2011, in time for the start of that academic year.

"It's a tremendously exciting time in Penn's history, to be able to add a significant amount of open space adjacent to the campus in an economic climate like this," said Anne Papageorge, Penn's vice president for facilities and real estate services.

Penn in 2004 purchased 14 acres from the Postal Service and announced plans for the park, two office towers with a mix of university space, retail and residential areas, and a 2,400-space parking garage. The park project also includes 10 acres previously owned by the university.

A developer purchased the postal building from Penn - making Penn's net cost for the postal lands $12 million - and will lease it to the IRS after renovations are complete. Construction of the garage also is under way and is scheduled to be completed next summer, and plans are in the works for the towers.

But Papageorge said the towers project, in partnership with Brandywine Realty Trust, may be delayed given the economy.

Their construction could be "impacted by the credit markets and just the fact that people are not really making bold moves into new space in this economy," she said. The towers are scheduled to be completed between 2012 to 2014.

Penn will occupy about 100,000 square feet of the 40- to 50-story office tower on Walnut Street, with commercial space on the ground floor. The 25- to 30-story tower on Chestnut Street would be residential, and might include some boutique office space, she said.

Penn president Amy Gutmann has called the project, estimated to cost $1.94 billion, a new "Gateway to the University."

"For far too long, these 24 acres of pure potential stretching along the west bank of the Schuylkill River have been buried under a cold carpet of asphalt and concrete," Gutmann said in a statement yesterday.

Gutmann, along with the board of trustees, in town for a scheduled meeting, will celebrate at a groundbreaking for the park this afternoon, which coincides with Homecoming weekend.

Penn Park was created in part to respond to the community's desire for more green space, Papageorge said. While the fields will be fenced in, and usage will have to be scheduled, the park will be open to the public, she said.

The park will span Walnut Street to just south of South Street and from the Amtrak rail lines to the east to the SEPTA rail corridor on the west. The landscape-architecture firm Michael Van Valkenburgh Associates of Cambridge, Mass., is leading the project.

The park will include an inflatable structure that will enclose one of the fields in colder months so it can continue to be used.

Three multipurpose athletic fields, 12 tennis courts, a raised central plaza, and gradually descending walkways also are planned. The bike trails will connect to the trails on the Center City side of the Schuylkill through bridges.

The park will include a system to harvest storm water and irrigate fields, and feature native plants, trees, and energy-efficient lighting.

Contact staff writer Susan Snyder at 215-854-4693 or ssnyder@phillynews.com.