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TOWNSVILLE, Australia — On the 12th day of rain, Ross and Kate Bennett were among the only residents on their street, where the water had risen so high that at one point, Ms. Bennett couldn’t walk into her yard, lest she be swept underwater.

After the record-breaking rains subsided, they looked around: The furniture was soggy. The car was soggy. The dogs, Cuddles and Murphy, were soggy.

In street after street across Townsville, a coastal city in Australia’s far north, the same story played out in the aftermath of what the authorities called a catastrophe of “unprecedented” rainfall, which brought flooding, crocodiles into the streets, sewage bubbling up out of toilets and, in one week, more water than the city normally receives in a year.

Over the course of the floods, two people died, 1,000 people were evacuated, 18,000 residents lost power and at least $74 million in insurance claims have been filed. Yet during and immediately after the disaster, many residents rallied to help one another in ways that mental health experts said were critical for people’s ability to recover from disasters and cope with future ones.