2.2 How can a river change the land?

1. 2.2 How can a river change the land?

2. What is the discharge of a river? A river can shape the land through exogenetic processes, including ________, ______________ and ___________. transportation erosion deposition The energy determines the kinds of work a river can do. discharge The __________ of a river indicates the amount of energy of a river. How can we know the amount of energy of a river?

3. What is the discharge of a river? volume It is the _______ of water in a river passing a given cross-section of its channel within a given amount of time, i.e. its ________. velocity Area of stream cross-section (A) = W  D (in the unit of m2) Velocity (V): Velocity (V) Measured by an instrument, in the unit of ‘m/sec’ Stream width (W) Discharge (Q) Average depth (D) =AV (Answer in the unit of m3/sec) The (larger / smaller) the discharge, the more the energy a river has.

4. Energy of a river What are the factors affecting the energy of a river? 1 Amount of channel water 2 Speed of water flow

5. Energy of a river What are the factors affecting the energy of a river? 1 Amount of channel water 2 Speed of water flow A Channel gradient B Channel friction

6. How can a river erode the land? River water can erode rock materials from the banks and bed through ______________. fluvial erosion The rate of erosion is high when: - the energy of the river is (low / high). - the resistance of the rocks is (low / high).

7. How can a river erode the land? Three directions of fluvial erosion Direction of fluvial erosion Vertical erosion / Downcutting Lateral erosion Headward erosion

8. Three directions of fluvial erosion Vertical erosion / Downcutting A river removes rocks from its _____. bed The valley will be _________. deepened

9. Three directions of fluvial erosion Lateral erosion A river removes rock along the _______. banks widened The valley is ________.

10. Three directions of fluvial erosion Headward erosion Loose rock debris is brought down by the _________ flow behind the river source. overland The river source extends (forward / backward). The valley is increased in _______. length

11. How can a river erode the land? Four ways of fluvial erosion Physically and chemically. No. It can also reduce the size of the rock materials. In what ways can erosion take place? Does erosion by water just remove the rock materials?

12. How can a river erode the land? Four ways of fluvial erosion Ways of fluvial erosion Abrasion Attrition Hydraulic action Corrosion / Solution

13. ________ power of river ___________ of rock How can a river erode the land? What factors control the rate of erosion of a river? Angularity, amount and weight of load Speed of water flow Erosive Amount of channel water Rate of fluvial erosion Water quality (Acidity, temperature) Rock structure Resistance Mineral composition

14. How can a river erode the land? What factors control the rate of erosion of a river? How do human activities cause more fluvial erosion?

15. Large particles hop and bounce along the river bed Small particles are carried in the water without touching the river bed Dissolved minerals carried by water Solution Very large particles roll or slide on the river bed In what ways does a river carry its load? Four ways of transportation The downstream movement of eroded material is called ______________. transportation Suspended load Suspension Bed load Dissolved load Bed load Traction Saltation

16. In what ways does a river carry its load? What factors control the amount of load in a river? Why are the colour of these two rivers different? Because they carry different amount of load.

17. In what ways does a river carry its load? What factors control the amount of load in a river? 1 Energy for transportation Larger amount of channel water A river can carry (more / less) load (More / Less) energy for transportation OR A river can carry (heavier / lighter) load Higher speed of water flow

18. In what ways does a river carry its load? What factors control the amount of load in a river? 2 Rate of erosion The erosion rate of the river basin controls the supply of _____. load (Dense / Sparse) vegetation helps hold the soil and prevents it from fluvial erosion.

19. In what ways does a river carry its load? What factors control the amount of load in a river? 3 Presence of lakes The lakes along the river channel help trap the load. The amount of load in the river then become (smaller / larger).

20. What makes a river lose its energy? Deposition ____________ occurs when a river loses its energy. sediment The deposited materials are called __________. Amount of channel water decreases (More / Less) energy for transportation The load deposits OR Speed of water flow decreases

21. What makes a river lose its energy? How does a river drop its load? Please click below for footage Is there a sequence of deposition? Yes, there is. What is the sequence? The largest and heaviest sediment deposits first. The smallest and lightest sediment deposits last.

22. What makes a river lose its energy? How does a river drop its load? What is a sequence of deposition of these four load? The (lightest / heaviest) load will deposit first and form the bottommost layer. The finest one forming the top layer.

23. What makes a river lose its energy? How does a river drop its load? The load forms layers at different distances from the mouth of the river. River Pebbles and sand Silt Clay Sea

24. The end

25. 1 Amount of channel water What are the other three kinds of water flow? The water flowing in a river channel is called ________ flow. _________ flow, ________ flow and _____ flow. Overland channel through base These three kinds of water flow will supply water to the channel flow.

26. Rainfall Evaporation Overland flow Throughflow Infiltration Base flow 1 Amount of channel water The amount of channel water increases when there is: (more / less) rainfall and snowmelt. Vegetation cover (more / less) evaporation. a (larger / smaller) catchment area. Drainage density (more / less) vegetation cover. Gradient a (faster / slower) infiltration rate. a (steeper / gentler) slope gradient. a (lower / higher) drainage density.

27. 2 Speed of water flow A Channel gradient Which channel has a higher energy? Which channel has a greater speed of flow? Channel A. Channel A. Channel A Channel B The steeper the gradient, the (slower / faster) the flow, and the (higher / lower) the energy.

28. 2 Speed of water flow B Channel friction Why does friction affect the speed of water flow? What factors affect channel friction? It (prevents / helps) water from flowing downstream. Energy is needed to overcome friction. Lesser energy causes water flows (faster / slower).

29. Do you know which channel has a greater speed of flow? a Channel shape The perimeter of the banks and bed which are in contact with the water is called the . wetted perimeter The wetted perimeter of Channel A: = 21m 9m + 6m + 6m The wetted perimeter of Channel B: = 24m 3m + 3m + 18m Channel A Channel B Channel (A / B) has a shorter wetted perimeter (more / less) energy (less / more) friction The speed of flow becomes (faster / slower) in Channel A.

30. a Channel shape Look at the three channels shown. They are of the same cross-sectional area. b Square a Semi-circular Which shape of channel produces the lowest friction? c Wide and shallow The _____________ one produces the lowest friction. semi-circular

31. Same cross-sectional area Same cross-sectional area Channel A Channel B b Channel roughness Channel (A / B) is rougher. The wetted perimeter of Channel (A / B) is longer. Channel (A / B) has greater friction and lower speed of flow.

32. How can a river erode the land? Four ways of fluvial erosion Abrasion The wearing away of the bed and banks by the _____ carried by a river. load Abrasion is the main process in ________ erosion. vertical The channel becomes less ________. uneven Please click above for animation

33. How can a river erode the land? Four ways of fluvial erosion Attrition The load in the river _______________ each other and break down into small pieces. knocks against The load becomes (larger / smaller) and (rectangular / rounder) downstream. Please click above for animation

34. How can a river erode the land? Four ways of fluvial erosion Hydraulic action running water The _____________ breaks up the river bed and banks. The running water is forced into cracks at the banks. The cracks are (enlarged / reduced). Rocks are loosened and removed. Please click above for animation

35. How can a river erode the land? Four ways of fluvial erosion Corrosion / Solution Water dissolves and removes the _______ minerals from rocks. soluble calcium For example: ________ in limestone. The rocks are weakened and easily broken up. Please click above for animation