the flood tax was for the 1936 flood not the 1889 dam related flood. The geography of the area causes floods every several decades.
15 years after 1936 the legislature wanted to create a permanent state liquor tax, they decided to use the existing Johnstown Flood tax as a short cut to that goal. If it didn’t have that name it would be called something else, but either way there would still be a permanent state liquor tax and it is not earmarked for flood relief.
The "temporary" tax was enacted in 1936 to help victims of the Johnstown flood. In the years immediately following prohibition, it was a 10 percent tax on liquor designed to help a community rebuild, according to a report published by the Pennsylvania Treasury." link