River Processes

Question 1

effect of headward erosion

Answer 1

makes the river longer.
happens near a rivers source as throughflow and surface runoff causes erosion at the point the water enters the river channel (the valley head)

Question 2

effect of vertical erosion

Answer 2

deepens river channels

happens in the upper stages of a river

Question 3

effect of lateral erosion

Answer 3

makes the river wider

happens in the middle and lower stages of a river

Question 4

5 ways in which erosion can occur

Answer 4

hydraulic action
abrasion/corrasion
attrition
cavitation
corrosion/solution

Question 5

what is hydraulic action

Answer 5

pressure of water breaks rock particles away from the bed and banks - its strongest in rapids and waterfalls and during floods

Question 6

what is abrasion

Answer 6

eroded pieces of rock in the water scrape and rub against the bed and banks, removing material. most erosion of river beds and banks happens by abrasion

Question 7

what is attrition

Answer 7

eroded rocks smash into each other and break into smaller fragments
their edges also get rounded off as they rub together
attrition doesn’t erode the bed and banks - it just makes the particles of rock in the river smaller and more rounded

Question 8

what is cavitation

Answer 8

air bubbles in turbulent stretches of water implode causing shockwaves that break pieces of rock off the banks and bed

Question 9

what is corrosion/solution

Answer 9

the dissolving of rocks by chemical processes
carbon dioxide dissolves in water to form a weak acid which reacts with rocks like limestone and chalk, breaking them down

Question 10

4 types of transportation

Answer 10

solution
suspension
saltation
traction

Question 11

what is solution

Answer 11

substances that dissolve are carried along in the water - e.g limestone is dissolved in water thats slightly acidic

Question 12

what is suspension

Answer 12

very fine material, like silt/clay particles, is whipped up by turbulence (erratic swirling of water) and carried along in the water. most eroded material is transported this way

Question 13

what is saltation

Answer 13

larger particles, like pebbles/gravel, are too heavy to be carried in suspension. instead the force of the water causes them to bounce along the river bed

Question 14

what is traction

Answer 14

very large particles, e.g boulders, are pushed along the river bed by the force of the water

Question 15

material transported by traction/saltation is called

Answer 15

the rivers bedload

Question 16

how can the speed and energy of a river be reduced (5)

Answer 16

1. reduced rainfall causes lower discharge, which means the river slows down and has less energy
2. increased evaporation or abstraction also causes lower discharge
3. friction e.g in shallow areas close to the banks, reduces speed of river, reducing energy
4. when the river is forced to slow down, e.g before a narrow section of the channel, it loses energy
5. a lot of energy is lost when the river meets the sea (the sea absorbs the energy)

Question 17

what is the capacity of a river

Answer 17

the total load (measured in volume, weight or mass) that a river can transport at a given point
the load of a river can be divided into diff categories according to particle size - sizes range from fine silt/clay (less than 0.1mm diameter) to big boulders

Question 18

what does the competence describe

Answer 18

the maximum particle size that a river is capable of transporting at a given point

Question 19

what does the Hjulstrom curve show

Answer 19

relationship between river velocity and competence

also shows how processes of erosion, deposition and transportation vary with river velocity

Question 20

what is the critical erosion velocity curve

Answer 20

shows the minimum velocity needed for the river to put up (erode) and transport particles of diff sizes
it takes a higher velocity to erode material than it does to just transport material

Question 21

what does mean settling velocity curve show

Answer 21

the velocities at which particles of diff sizes are deposited. i.e it shows the competence of the river at diff velocities