CHAPTER 8: FLUVIAL PROCESSES, PATTERNS AND LANDFORMS (a) Hydraulic action (the force of moving water)
The force of moving water erodes the river channel. Fast-moving water forces out loose rock and earth from the riverbed and banks. Banks collapse as the turbulent water undercuts the river bank, a process known as bank caving. Bubbles of air in the turbulent water burst (cavitation) and the tiny shockwaves loosen the rocks and soil on the bed and banks making it easier to wash away.
(b) Abrasion (corrasion)
This is the wearing away of the riverbed and banks by its load. The load scrapes and smoothes the channel as it whirls and rolls along in the moving water.
(c) Attrition
This is when rock particles of the load hit off each other. This process gradually wears away the stones to make them smooth and round.
(d) Solution
Fig. 15 Erosion processes are active on the Owenreagh River, County Kerry.
This is the chemical process whereby river water dissolves the soft rock over which it flows. This process is very effective in limestone regions where soluble minerals are dissolved and transported away in solution. Discoloured river water is evidence of solution.
Processes of river transport
The load created by river erosion is transported by the river to a new location. Any material carried along the riverbed is called its bedload. River
transport processes are: (1) solution, (2) suspension, (3) saltation and (4) traction.
Silt and clay suspended by turbulence
(1) Solution The load is carried dissolved in the water. This load is invisible but may discolour the river water.
(2) Suspension Fine sediment is carried within the flowing water.Most of the river’s load is carried this way. This process gives the water a muddy brown appearance, especially seen during floods when turbulence keeps the sediment mixed up in the water.
Rolling
Dragging/ Sliding
Sand moving by hopping along bottom
Rock Gravel Fig. 16 The processes of river transport