Embankment Dam Failure Analysis (FEMA 541) - Association of ...

Dam name: South Fork (Johnstown)
Location: On South Fork Little Conemaugh River
Dam Characteristics:
Dam type: earthfill
Dam height: 72 feet
Dam crest length: feet
Reservoir volume: 11,500 acre-feet
Spillway:
History of Dam:
Purpose: Originally for supplying water to canal system; at time of failure was owned by South
Fork Hunting and Fishing Club of Pittsburgh.
Dam completed: 1853
Dam failed: May 31, 1889 about 3:10 pm (about 36 years old)
Failure cause: overtopping during an approximate 25-year storm (Drainage area of about 48 sq.
mi.)
Details on Detection of Failure/Deciding to warn:
People were at dam trying to prevent dam failure. Between 11:30 and noon the resident engineer,
on horseback, reached the town of South Fork (2 miles from dam) with a warning. Word was
telegraphed to Johnstown that dam was in danger.
Details on dissemination of warnings and technologies used:
Warnings were not widely disseminated.
Details on response to the warning:
• Little attention paid to warnings due to false alarms in prior years.
• At time of failure, Johnstown was inundated by up to 10 feet of floodwater.
Description of flooding resulting from dam failure: Floodwater reached Johnstown, mile 14,
about 1 hour after failure. Large number of buildings destroyed.
The losses included: about 2,209 fatalities; 20,000 people at risk.
All, or nearly all, of the fatalities occurred in the first 14 miles downstream from South Fork
Dam.
Prepared by Wayne Graham