Fig. 8.7 The wetted perimeter of a river channel.
Processes of river transportation
Rivers transport material once they have eroded it (Fig. 8.8). This transportation takes place through: zz
solution: dissolved rocks such as limestone are carried in a solution (this requires least energy);
zz
suspension: light materials such as sand and clay are carried by the moving water as a suspended load; this is commonly seen in times of flood when they turn the water a muddy brown colour;
zz zz
saltation: small, light rocks/pebbles are bounced along the riverbed;
traction: heavy materials are rolled/dragged along the riverbed (this requires most energy).
River deposition Rivers deposit their loads when: zz
A-Z
Wetted perimeter: The area of the riverbed and bank that comes into contact with water.
their volume decreases. A river’s volume
decreases when: ƒzthere is a dry season or it enters a hot, dry region with high evaporation rates;
ƒzpermeable rocks such as limestone allow water to pass through them;
ƒzflood waters recede; ƒzwater is taken from the river for agricultural, industrial or domestic use.
zz Traction Saltation Fig. 8.8 Processes of river transportation.
their speed decreases. The speed of a river decreases when: ƒzit enters a sea, lake or a gently sloping plain;
ƒzthere is an increase in the roughness of the channel. CHECK YOUR LEARNING
1. Where is the source of a river found? 2. What is the tidal point of the river’s mouth called? 3. How would you recognise a ‘dendritic’ drainage pattern on an OS map? 4. Where would you expect to find a ‘radial’ drainage pattern? 5. Glacial deposits have a big impact on the formation of what type of drainage pattern? 6. Explain the process of ‘cavitation’. 7. Name one rock type that can be eroded by the process of solution and explain how this occurs. 8. Explain why a river may be brown in colour when in flood.
