Fluvial Landforms – Waterfalls and Rapids

‘Fluvial’ means of the river or found in a river. Moving water is very powerful. Rivers are always at work changing the channel they flow in and the landscape surrounding them. The erode rock and deposit sediment and broken rock elsewhere producing distinctive fluvial landforms.

Rivers always flow from a high point to a low point. Base level is the lowest level to which a river can flow and this is usually sea level. A river changes shape, becoming deeper and wider near the mouth.

The longitudinal profile shows the length of the river from source to mouth and its descending path towards the sea. The transverse profile shows the shape of the river channel. ie: width and depth

  • Near the source (upper end), the channel is narrow and steep. Vertical erosion is dominant
  • In the middle, the slope is gentle and the channel wider. Lateral erosion dominates.
  • Near the mouth, the valley flattens and the channel is wide and deep.

Fluvial Landforms

Rivers erode, transport and deposit forming fluvial landforms.

Erosion is the wearing away and removal of rock and soil.

Deposition is the process in which a river drops its sediment.


A waterfall is a sudden, steep, vertical drop in a riverbed. Water plunges down this drop. This usually occurs where hard and soft rock meet. The soft rock erodes more quickly forming a steep cliff.

Famous waterfalls in South Africa:

Howick Falls in KwaZulu-Natal is 95m meters tall.

Tugela Falls in the Drakensbers is 947m tall making it South Africa’a highest waterfall and the second highest in the world after Angel Falls in Venezuela.

Mac Mac Falls in the town of Sabie in Mpumalanga

The spectacular Augrabies Fall on the Orange River in the Augrabies Falls National Park in the Northern Cape. The river has a massive canyon. The local Khoi people call it the ‘Plae of Great Noise’.

Rapids are fast-flowing, turbulent sections of the river where there are steps in the riverbed. Rock obstacles change the river’s flow from laminar to turbulent and the churned up water is referred to a whitewater. Rapids form when a river flows over a bed of erosion-resistant rock and wears away weaker rock downstream creating a steep slope.