Today I spent the day at the Archives and was perusing the records of St. Mary Catholic Church in Allegheny City. I was looking for a death for a client.
I came to a page in the handwritten index and I noted that five people of the Fuchs Family had died on 26 July, 1874. I made a note because I thought that was so interesting because they had died from aqua submersion, or drowned.
After I found the information for the client I went back to read it again and below and above I found families that all had died from drowning. My co-researcher said that she remembered that there was a terrible flood one year.
When I got home I Goggled the date and Pittsburgh Flood:
“As evening fell on 26 July 1874, "a storm of unprecedented violence closed over this vicinity, and continued for upwards of an hour, during which the fall of water was something enormous, and the display of electricity unparalleled within the memory of any living citizens," reported an almanac of local history in 1876. Butcher's Run, Spring Garden Run, Pleasant Valley, and Woods Run injected flood waters into the city of Allegheny, Pennsylvania. All four streams coursed down from the northern hillsides, spilling over their banks into lower urban areas. Butcher's Run and Spring Garden Run flooded from their confluence a half mile to the river, pouring water into a heavily populated section of the city.  Steep hillsides focused the swollen streams. An observer declared that the flooded valleys
each contained a roaring river, carrying everything before it, -- buildings and their contents, corpses of human beings, dead animals of every description, horses, cattle, hogs, sheep, and mules, household furniture, mountains of clay, sand, and gravel, street lamps, fences, etc., etc., all borne upon its raging bosom toward the river below. 
Residents caught in the storm that Sunday evening had no warning. Property lost in the Butcher's Run flood could not be accurately tallied, but contemporaneous sources estimated several million dollars of material damage. About seventy Allegheny residents died, with up to eighty more perishing outside of the city. The greatest devastation centered on the Butcher's Run and Spring Garden Run watersheds, although Woods Run, in what was to become Riverview Park, also left destruction its path. "It was a terrible visitation, and should be a most solemn warning to the people, teaching them not to neglect the necessary precautions, and to never disregard the possible power of the elements," summarized the 1876 almanac. 
In 1896, another inundation revived memories of the 1874 Butcher's Run flood, burying railways under debris and forcing Allegheny residents to evacuate from many of the same areas. "Within minutes after the storm broke, Woods Run avenue was covered with several feet of water and much damage was done between the cemeteries and Washington avenue," reported the Pittsburg Post. A particularly steep sewer along Woods Run Avenue carried so much water.”
FATAL FLOOD 1876 It seemed to be about 126 people who lost their lives. In one article I read was that the event was considered “an act of God” and no one was held responsible.