He worked on the Plougastel Bridge and in 1928 was appointed as the chief engineer of dams in the Upper Dordogne River.
A few years later, on 2 December 1959, the dam abruptly broke and collapsed, releasing a 50-meter-high (160 ft) wall of water that reached the nearby town of Fréjus, killing 423 people.
It was said that Coyne was deeply affected by the dam's failure, and immediately blamed himself, claiming he was solely responsible.
Indeed, Coyne did not implement the advice of Georges Corroy, a geologist, to build the dam 650 ft upstream, nor did he adapt the spillway gate to the flood flow.
Other factors were blamed instead, including the location of the dam, the stability of the rock material, the fact that a geological fault was found on the site, and heavy rain that had raised the water level by 15 feet that year.