The flood was preceded by rains from March 9 that did not stop until March 22 , 1936 . The storms brought warmer 50 °F ( 10 °C ) weather that was a cause of one stage of flooding and the continuous rains a second cause of flooding . The natural run-off of 1 to 3 inches ( 2.5 to 7.5 cm ) was far surpassed by the deluge of from 10 to 30 inches ( 25 to 75 cm ) of water in the region . The flood came before pending flood control legislation was enacted or any significant flood control measures implemented . The narrowness of the valleys and encroachment of buildings on the river banks contributed to record flooding . By the time nightfall came one-third of the city was under of water and by the time flooding was over twenty-five people lost their lives . The damages , estimated at $ 43 million , made it the worst flood since the flood of 1889 and the event is chronicled at the Johnstown Flood Museum After the flood , sweeping nationwide flood control laws were enacted and from 1938 to 1943 Johnstown saw many projects completed . These measures gave the people the feeling that the area was now " flood free " , and it was touted as such until the flood of 1977
flood of 1889
Johnstown Flood
Johnstown flood of 1936