NEW YORK (AP) - The waterfalls of the Sept. 11 memorial at ground zero are showing signs of life.
Engineers began testing one of the twin waterfalls on Tuesday, circulating hundreds of thousands of gallons of water into the north reflecting pool.
The cascades are the largest manmade waterfalls in North America, and they empty into pools that mark spots where the World Trade Center towers once stood.
The 176-foot-perimeter pools are the centerpieces of Michael Arad's "Reflecting Absence" memorial plaza, which will cover nearly half the 16-acre lower Manhattan site and will be surrounded by thousands of trees.
The head of the foundation overseeing the memorial, Joe Daniels, said that even though Tuesday's tests were aimed at assessing the flow and circulation of the water, the aesthetics were "stunning."
"It's really what the memorial is - the falling water and the sound," he said, adding it would "create the peaceful place that we hoped it would be."
The tests, which began about 11 a.m. and continued throughout the day, focused largely on eight pumps that will circulate 52,000 gallons of water a minute. During the testing, more than 350,000 gallons of water streamed into the north pool.
Chris Ward, executive director of the Port Authority of New York and New Jersey, which owns the trade center site, said in a statement that the testing was "an important sign of progress."
"Sept. 11, 2011 is the only goal that matters, and for the next 306 days, we will continue to keep our heads down and locked in on delivering the sacred heart of the site," he added.
Testing of the waterfalls of the south pool is expected to begin in the spring of 2011, almost 10 years after Islamic extremists destroyed the World Trade Center and killed nearly 2,800 people on Sept. 11.
In January, a 40-foot-wide waterfall mock-up was created and tested in a field in Brooklyn to get the right veil of water over a small dam with fingerlike structures that make the water flow in rivulets.
When finished, the waterfalls and bronze panels bearing the names of the Sept. 11 victims will be backlit at night.
Memorial builders expect to have the waterfalls fully installed by spring so that they can run by Sept. 11, 2011.