River Systems and Geomorphic Processes

Key River Terminology

The source is the start of a river, while the mouth is the end of a river where it meets the sea. Tributaries are defined as smaller rivers flowing into a larger river.

The Courses of a River

Rivers are divided into three main sections: the upper course, the middle course, and the lower course. The upper course features steep land gradient, a narrow and shallow channel, slow river speed, a sediment load consisting of large boulders and rocks, and landforms such as waterfalls.

The middle course features land that is quite flat, a channel that is quite wide and quite deep, fast river speed, a sediment load made up of smaller rocks and pebbles, and landforms including meanders and ox bow lakes.

The lower course features land that is very flat, a channel that is very wide and very deep, river speed that is slowing down, a sediment load composed of silt and sand, and landforms such as floodplains and deltas.

Geomorphic Processes and Erosion

Geomorphic processes refer to ways in which the land can be shaped, derived from geo meaning earth and morphic meaning change. Erosion is the specific geomorphic process of wearing down rocks in a river, occurring in four different ways.

Hydraulic action occurs when air and water is forced into cracks in the river bed and banks, causing them to break and wear away. Abrasion occurs when rocks being carried along the river wear down the river bed and banks like sandpaper. Attrition occurs when rocks in the river are smashed together and break into smaller, rounder and smoother particles. Solution occurs when dissolvable particles are dissolved into the river.

River Transportation

Transportation is the movement of rocks along the river floor, which takes place through four distinct mechanisms.

Traction involves boulders and rocks being rolled along the river bed. Saltation occurs when small pebbles and stones are bounced along the river bed. Suspension is when fine, light material is carried along by the river. Solution happens when minerals are dissolved in the water.