Summary
Highlights
Attrition is the process where sediment particles knock against each other and the riverbed, becoming smaller and adding to the suspended load, also contributing to lateral and vertical erosion of the channel.
Abrasion occurs when boulders and stones wear away the river banks and bed through knocking actions, contributing to both lateral and vertical erosion and linking to saltation in the bed load.
The video introduces the topic of stream load, a new addition to the 2021 Grade 12 geomorphology examination guidelines, and aims to connect it with fluvial processes and river profiles.
Stream load is defined as all solid matter or materials transported by a stream.
The first type is bed load, which consists of heavier materials like sand, gravel, and boulders that roll, slide, or bounce along the riverbed. This movement occurs through saltation (small rocks bouncing) and traction (heavier materials rolling).
Suspended load includes lighter materials such as silt and clay that are carried in suspension within the stream water.
Dissolved load refers to materials carried as dissolved solids in the stream water, often referred to as the 'invisible load' due to the particles being dissolved.
The video discusses how erosion processes, involving stream load, impact the river channel. It distinguishes between lateral erosion (making the channel wider) and vertical erosion (making it deeper).
Hydraulic action, the force of fast-flowing water hitting the bed and banks, uses suspended and dissolved loads to erode cracks, leading to vertical erosion in the upper river course and lateral erosion in the lower courses, forming features like meanders.
Solution, or corrosion, involves acidic water dissolving rocks like chalk and limestone, contributing to the river load and causing both vertical and lateral erosion, thereby widening and deepening the valley.