SAN ANTONIO - Extending San Antonio's popular River Walk by almost two miles faced an age-old problem for watercraft that was solved with the ingenious use of a lock system that - on a much smaller scale - works the same way the locks do on the Panama Canal.

In Panama, and on the San Antonio River, the elevation changes as you go upstream, requiring locks that capture water and float vessels up or down. For San Antonio, the need was to lift 40-passenger barges nine feet, so they could continue upriver on the new Museum Reach portion of the River Walk.

The Museum Reach has made an inviting public amenity out of a waterway that for years was so overgrown "you didn't even know there was a river there," said Suzanne Scott, general manager of the San Antonio River Authority.

Scott and a team of designers and engineers hired by the authority, a four-county agency that oversees flood control and managed the improvement project, studied larger lock systems for cargo ships on the Great Lakes before determining that something similar would work here.

As barges operated by Rio San Antonio Cruises approach one of the two locks, gates open and the boats enter - very carefully. The barges are 11-by-27 feet and the locks measure 13-by-30. The gates are closed behind the barge, and water is pumped from below to fill the lock.

After five minutes, another set of gates opens at the opposite end, and the barge continues upstream. The same process, in reverse, takes place for barges headed downstream. Two of the vessels can be in the side-by-side locks at the same time, helping keep traffic flowing.

Mark Sorenson, the river authority's Museum Reach project manager, explained during a tour before the opening that the locks could be filled in less than five minutes, but at that speed, the barges don't bounce off the walls.

The locks added $6.5 million to the $72 million cost of the Museum Reach. AT&T, which until last year had its corporate headquarters in San Antonio, in a building overlooking the Museum Reach, donated $5 million of the cost.

- Tom Belden