NSW floods explained — and why Sydney is at risk when it rains

They’re found in many homes around the country, but what you may not know is the humble bathtub holds the key to explaining Sydney’s flood danger.

Australia’s largest city is often described as being in the “Sydney basin” — particularly apt term right now, as it’s experiencing something known as the “bathtub effect”. 

It’s what happens when a lot of water is tipped into a low-lying area (like Sydney) and it can’t escape quickly enough.

When it rains, the water that’s dumped on the ground eventually drains into rivers and ultimately the ocean.

If a lot of rain is trying to escape from somewhere at the same time, low-lying areas can fill up like a bathtub while the deluge makes its way through one small point (like a plug hole).

A quick…