The phrase "a calamitous decision" is correct and usable in written English.
It can be used to describe a decision that leads to significant negative consequences or disaster.
Example: "The board's choice to cut funding for safety measures was a calamitous decision that resulted in severe repercussions."
Alternatives: "a disastrous decision" or "a catastrophic choice".
It was a truly calamitous decision, making him and his hapless son, James, look decidedly foolish and weak-willed.
From there things unravelled, with Finn admitting "a few calamitous decisions" were made along the way, and by the time the Ashes tour to Australia came round, he had lost confidence in his action while searching for "a golden nugget of information" that would remedy things – before being sent home by the then one-day coach Ashley Giles.
The huge rise in the price of ivory that makes it a profitable commodity for terrorists came after the calamitous decision by CITES in 2008 to sanction the sale of ivory stockpiles, thereby re-opening the global market that had been closed down since 1989.
Several network executives said they would not consider cutting back on budgets for developing scripted shows, citing ABC's calamitous decision to do that when it had "Who Wants to Be a Millionaire" showing as many as four nights a week.
Quote "It's the most calamitous decision of our generation".
On top of everything else, Peña Nieto made the calamitous decision, in August, 2016, to invite Trump to Mexico.
Let all those who believe in democracy, and in justice, try to keep cool and courageous and do their duty in face of this calamitous decision.
According to Variety, Greengrass has long been critical of the Iraq war, describing the invasion as "the most calamitous decision of our generation".
He was never certain what to do with the Daily Star and in 1987 made the calamitous decision to give the Sunday Sport publisher, David Sullivan, editorial and marketing control over the Star.
Kerry — who was influenced by the relatively successful, if belated, interventions in the Balkans, in the nineties, and also by the calamitous decision not to intervene in Rwanda in 1994 — joined this chorus when he replaced Clinton.
