"heavy downfall" is correct and usable in written English.
You can use it to refer to a large amount of rain, snow, or hail falling in a short period of time. For example: "We had a heavy downfall last night, so the streets were flooded this morning."
His downfall is a heavy blow for the chancellor, for both parties and for the health of politics in Germany generally.
In the past, teams have complained about the Wembley pitch being too heavy, but there was a downfall of rain here in North London yesterday, while today has been glorious sunshine – those conditions should make the surface soft but not boggy, ideal for two teams who prefer to play on the ground rather than relying on power tactics.
The fund gets gold stars for its performance in 1998 and 1999, with returns up 40.5% and 21.8% respectively, but its heavy tech focus was its downfall.
At the previous summit, in Vilnius in late 2013, Ukraine's then-president, Viktor Yanukovych, triggered domestic protests that led to his downfall by rejecting, under heavy Russian pressure, a free-trade agreement with the EU.
The Kazakh example is a good case in point because, first of all, collectivization initiated an exodus of millions of Kazakh nomads and inflicted heavy losses of life; then, a downfall in animal production required a number of years to be compensated.
Three months later Chennault told United States President Franklin D. Roosevelt that a force of 105 modern fighters and 40 bombers (including 12 heavy bombers) would be able to "accomplish the downfall of Japan" within six to twelve months.
Schmidt paid a heavy price because the issue split his party and contributed to his downfall in 1982.. The fact that Schmidt's loyalty to the West was unquestioned had made it easier for him to continue the Eastern policies initiated by Brandt.
Both works had as much to do with social issues as with artistic ones, and certain heavy-handed leanings were their downfalls.
