As Bruce O says above, the source of the lyrics in the Digital Tradition is Louise Pound: American Ballads and Songs (1920 reprinted 1972, Charles Scribner's sons, New York).
According to Pound, the text was known to May B. Wimberly of Lincoln, Nebraska, 1917. The subject is plainly the Johnstown Flood of 1890 (sic), but the title as given by Mrs. Wimberly is retained.
I submitted a corrected version of the lyrics to the Digital Tradition. I can't figure out where the reference to Rickaby came from.
Here's the story, as told at the Website of the National Park Service:

There was no larger news story in the latter nineteenth century after the assassination of Abraham Lincoln. The story of the Johnstown Flood has everything to interest the modern mind: a wealthy resort, an intense storm, an unfortunate failure of a dam, the destruction of a working class city, and an inspiring relief effort.
The rain continued as men worked tirelessly to prevent the old South Fork Dam from breaking. Elias Unger, the president of the South Fork Fishing and Hunting Club, was hoping that the people in Johnstown were heeding the telegraph warnings sent earlier, which said that the dam might go. When it finally happened, at 3:10 P.M., May 31, 1889, an era of the Conemaugh Valley's history ended, and another era started. Over 2,209 people died on that tragic Friday, and thousands more were injured in one of the worst disasters in our Nation's history.
Johnstown Flood National Memorial is located in southwestern Pennsylvania, about 10 miles northeast of Johnstown. The park contains nearly 165 acres and preserves the remains of the South Fork Dam and portions of the former Lake Conemaugh bed.

-Joe Offer-