Kōkiri Learn

Background reading · Social Sciences

From the mountain to the sea: how a river system works

Every river is a whole system: a catchment, tributaries, bends, a floodplain and a mouth. Here is how it fits together.

Rain that falls on a hill does not stay put. It trickles into a stream, the stream joins another, and eventually the water reaches a river and the sea. Everything that water touches on the way is part of one system.

Key words

  • Catchment: all the land that drains into one river. Its edges are the ridges and hilltops. Rain that falls inside the catchment ends up in that river.
  • Tributary: a smaller stream or river that joins a bigger one. The place where they meet is a confluence.
  • Source and mouth: where the river begins, often on a mountain, and where it ends, at the sea or a lake.
  • Floodplain: the flat land beside the lower river, built up over thousands of years from sand and silt dropped by floods.

    • Three sections

    In the upper course, the river is steep, narrow and fast. It cuts down into rock, making gorges and rapids. In the middle course, the land flattens and the river starts to swing in bends called meanders, leaving flat terraces. In the lower course, the river is wide and slow. It drops the sand and silt it has carried, building a floodplain and sometimes a delta or estuary at the mouth.

    The Whanganui

    The Whanganui River begins on the slopes of Mount Tongariro in the central North Island and flows about 290 km to the Tasman Sea at Whanganui. It is the third-longest river in Aotearoa and passes through more than 200 rapids and deep papa (mudstone) gorges. For centuries it was a highway: waka carried people and goods, and settlements and marae lined its banks. Later, riverboats carried tourists and mail as far as Pipiriki and Taumarunui.

    Why people settle beside rivers

    Rivers give fresh water, food such as tuna (eels) and fish, fertile flat land for gardens, and a route to travel. That is why so many towns are built on floodplains, and why floods matter so much.

    Sources and further reading

    Written for Kōkiri Learn students in our own words. Check facts against the sources.

    Used in: Te Awa Tupua: Rivers, Floods and People