Sydney braced for its worst flooding in decades after record rainfall caused its largest dam to overflow and as deluges prompted mandatory mass evacuation orders along Australia’s east coast. Emergency services ordered people living in low-lying areas on the city’s northwestern fringes to flee to safety, as authorities warned of a potentially “life-threatening” situation in the state of New South Wales. It came after the Warragamba Dam, which provides much of the drinking water for Sydney, spilled over Saturday afternoon – causing officials to warn the downstream Hawkesbury River was expected to peak at levels not seen since 1961.