NEW YORK, NY (AP).- The waterfalls meant to evoke memories of the Sept. 11 dead stand three stories high in a field in Brooklyn, spilling down into a pool. Four large American flags poke through the grass to mark off each corner of a World Trade Center tower footprint. For more than three weeks, builders of the Sept. 11 memorial have been tinkering with details like water flow and year-round heating with a mock-up of the cascades, part of Michael Arad’s “Reflecting Absence” memorial at ground zero. The architect saw the waterfalls — which will empty into huge reflecting pools set above the spots where the towers once stood — tested for the first time Friday as they were demonstrated for The Associated