The problem was doubled in the Lost Valley section, as flood waters backed up where the Raritan and Millstone rivers meet near the dam. All trapped and injured people had to be taken out by helicopter, as there was no way to get in or out of the Lost Valley section. The September 1999 flood disaster was the worst ever to hit Manville, although it had been flooded in 1971 during Tropical Storm Doria, when many of the Lost Valley houses were destroyed and their foundations lost, and previously before that in the 1950s. Because of the railroad tracks being so much higher than the Lost Valley land, Manville's Lost Valley will always be a number one target for flooding. Through research of Manville's history, Lost Valley was to remain open land due to the high risk of flood.