ENGINEERS DRAINED NIAGARA FALLS In 1969, engineers did the unthinkable when they shut off the American Falls, one of the three waterfalls of Niagara. By diverting the river with a temporary dam, they exposed the dry riverbed for several months. The goal was to study erosion, which has always been the driving force behind Niagara’s retreat. The falls erode because soft shale beneath the hard limestone cap is constantly worn away, causing massive rock collapses. Engineers and geologists wanted to