Upland Rivers

Fiordland Waterfall

Fiordland Waterfall, Image Julian Thomson

Mountain ridges separate rivers in different catchments (or drainage basins).

The largest scale example of this in New Zealand is Ka Tiritiri o te Moana, the Main Divide of the Southern Alps, which separates glaciers and rivers that flow to the east from those that flow to the west coast of the South Island.

Mountain rivers are characterised by steep slopes and fast water flow. They are highly erosive, often choked with large angular boulders and have many rapids and waterfalls.

On the lower slopes of the mountains, the water slows down and leaves behind the larger rocks and boulders. Occasional flood surges will shift heavier boulders further downstream than will occur during normal flow rates.