New York (CNN) -- Engineers working on the September 11 memorial
took a giant step this week when they began testing one of the
installation's twin waterfalls. The north pool waterfall,
located where the North Tower of the World Trade Center stood,
sprang to life Tuesday after years of planning by the National
September 11th Memorial and Museum. The waterfalls, designed by
architect Michael Arad, will be the center of the "Reflecting
Absence" memorial plaza, which is to open on September 11, 2011,
the 10th anniversary of the fall of the twin towers. By then the
falls are to be surrounded by a green space and framed by 400
trees. Joe Daniels, president of the memorial, said he was on
the site when the tests began. "To see the water coming down all
four sides of the north memorial pool took my breath away," he
said. "To see the veils of water fall in the pool was inspiring.
It was great." The waterfalls are the largest manmade falls in
the United States. The fall is 30 feet, and the water eventually
disappears