Question

Why were logjams called the "river man's ruin?"

Answer 1

Because many "River men," the men who were tasked with clearing the logjams, died while doing that dangerous job.

Answer 2

Logjams were called “river man’s ruin” given that there was always an inherent danger in them. As these men were working on the rivers trying to dismantle the log jams, these structures could fall apart, suddenly killing or hurting them. Any sudden change in water conditions (abrupt rains, snow melting after winter, any animal crossing by) could change these “sometimes stable” structures into real life hazards.