Water — the force that sorts the country

Water arrives with a bad reputation, and it half deserves it. On the sand coast it is the thief: it trickles down through the dunes and takes the iron, the colour and the phosphorus with it, leaving the poverty the wallum is built on. But theft is only half of what it does. Water is also the great connector, the medium the whole reef-to-range gradient dissolves in and rides on, and it takes one rainfall and sorts it into separate worlds depending on the road it takes down.

So watch where it goes, because the route decides almost everything. On the basalt range, rain lands on deep clay that holds it and lets it go grudgingly, which is why the hinterland stays green through the dry and its gullies run clear and cool. On the thin foothills the water hurries off, and the country hardens between rains. On the coastal sand it sinks straight down and vanishes into the body of the dune, where it may wander underground for years before it troubles a stream. Same rain, three grounds, three fates. Learn where the water goes and you have read, in advance, what is allowed to live there.

The sand hides the strangest of those waters. Stand on a dazzling dune in a drought and you seem to have found the least watery place on the coast. In fact you stand on the lid of an enormous freshwater store. A sand mass behaves like a colossal sponge: rain sinks in and gathers as a lens of fresh groundwater, floating, being lighter, on the denser saltwater creeping in from below. And the store is slow. On comparable sand masses a water molecule takes decades to work through, with mean ages measured from 37 to more than 150 years. That hidden sponge is why the heath never quite dies each dry season, dribbling water into roots and streams long after the last rain is forgotten. It is also what the whole community of wetlands, lakes and perennial streams leans on, bound so tightly to the groundwater level that drawing it down or fouling it can undo them with nothing whatever changing at the surface. The most resilient-looking country on the coast turns out to rest on something you cannot see from where you are standing.

Down on the flats, water works in pulses. The rivers here run short and steep, and flood hard. The Maroochy, the Mooloolah and the Noosa all rise nearby and reach the sea within a few tens of kilometres, so they climb from a quiet stream to a bank-topping torrent inside a day. For anyone living on the floodplain a flood can be pure disaster. But in ecological terms the flood is the point of the place. Spreading across the flat, it lays down nutrient and sediment, refills the swamps and lagoons, reconnects the scatter of off-channel waters that fish and waterbirds crowd into, and cues many of them to breed on the flood itself. A floodplain that is never allowed to flood, because it has been walled, drained and built over, quietly loses the wetlands, and the life, that the flooding sustained. Where fire is the renewal that looks like destruction on the dry ridges, the flood is its wet-country twin.

Along the way the water does its chemistry. Steeping through litter over sand too poor to buffer anything, it turns tea-dark and sour, and that blackwater shelters a handful of acid frogs found nowhere else. It also cups two kinds of lake in the dunes, told apart by how each one meets the buried store.

At the very bottom the fresh water hands itself to the sea, turns brackish and then frankly salt, and the sorting carries on, now by saltiness rather than by nutrient, banding the estuary as sharply as altitude bands the range. The rain that fell on the coast is one rain. What breaks it into all these worlds, poor, stored, pulsed, sour and salt, is never the rain. It is the route.