Darwin has two seasons - wet and dry. During the dry season (which can last up to nine months) there is very little rain. It can go over a hundred days straight with no rain! But during wet season, the monsoonal rains bring huge downpours.
Because of this, Darwin has many drainage systems built across it. Most of the year these stormwater drains and canals are dry (here, the grass looks dead - but dry and brown is normal) but during a good rain, this system can be knee deep in fast flowing water.
Because of all the drainage built in to Darwin, after the heaviest rains, nearly all the water will be gone after only an hour or two.