Part 2 Quit Landforms and exogenetic processes 2.2 How can a river change the land?

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

Part 2 Quit Landforms and exogenetic processes What is the discharge of a river? 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 ________. volume velocity The (larger / smaller) the discharge, the more the energy a river has. Area of stream cross-section (A) = W  D (in the unit of m 2 ) Velocity (V): Measured by an instrument, in the unit of ‘m/sec’ Discharge (Q) = A  V= A  V (Answer in the unit of m 3 /sec) Stream width (W) Average depth (D) Velocity (V)

Part 2 Quit Landforms and exogenetic processes What are the factors affecting the energy of a river? 1 Amount of channel water 2 Speed of water flow Energy of a river

Part 2 Quit Landforms and exogenetic processes What are the factors affecting the energy of a river? 1 Amount of channel water Energy of a river A Channel gradient B Channel friction 2 Speed of water flow

Part 2 Quit Landforms and exogenetic processes 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).

Part 2 Quit Landforms and exogenetic processes Vertical erosion / Downcutting Lateral erosion Headward erosion Direction of fluvial erosion How can a river erode the land? Three directions of fluvial erosion

Part 2 Quit Landforms and exogenetic processes A river removes rocks from its _____. The valley will be _________. bed deepened Three directions of fluvial erosion Vertical erosion / Downcutting

Part 2 Quit Landforms and exogenetic processes The valley is ________. A river removes rock along the _______. banks widened Three directions of fluvial erosion Lateral erosion

Part 2 Quit Landforms and exogenetic processes The valley is increased in _______. Loose rock debris is brought down by the _________ flow behind the river source. The river source extends (forward / backward). length Three directions of fluvial erosion Headward erosion overland

Part 2 Quit Landforms and exogenetic processes How can a river erode the land? Four ways of fluvial erosion In what ways can erosion take place? Physically and chemically. Does erosion by water just remove the rock materials? No. It can also reduce the size of the rock materials.

Part 2 Quit Landforms and exogenetic processes Ways of fluvial erosion Attrition Corrosion / Solution Corrosion / Solution Abrasion Hydraulic action Hydraulic action How can a river erode the land? Four ways of fluvial erosion

Part 2 Quit Landforms and exogenetic processes What factors control the rate of erosion of a river? How can a river erode the land? Rate of fluvial erosion ________ power of river ___________ of rock Erosive Resistance Angularity, amount and weight of load Speed of water flow Amount of channel water Water quality (Acidity, temperature) Rock structure Mineral composition

Part 2 Quit Landforms and exogenetic processes 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?

Part 2 Quit Landforms and exogenetic processes In what ways does a river carry its load? Suspension Traction Solution Saltation Suspended load Bed load Dissolved load The downstream movement of eroded material is called ______________. transportation Four ways of transportation Very large particles roll or slide on the river bed 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

Part 2 Quit Landforms and exogenetic processes 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.

Part 2 Quit Landforms and exogenetic processes In what ways does a river carry its load? What factors control the amount of load in a river? 1Energy for transportation Larger amount of channel water Higher speed of water flow A river can carry (more / less) load (More / Less) energy for transportation A river can carry (heavier / lighter) load OR

Part 2 Quit Landforms and exogenetic processes In what ways does a river carry its load? What factors control the amount of load in a river? 2Rate 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.

Part 2 Quit Landforms and exogenetic processes In what ways does a river carry its load? What factors control the amount of load in a river? 3Presence of lakes The lakes along the river channel help trap the load. The amount of load in the river then become (smaller / larger).

Part 2 Quit Landforms and exogenetic processes ____________ occurs when a river loses its energy. Deposition The deposited materials are called __________. sediment What makes a river lose its energy? Amount of channel water decreases Speed of water flow decreases (More / Less) energy for transportation OR The load deposits

Part 2 Quit Landforms and exogenetic processes Please click below for footage Is there a sequence of deposition? What makes a river lose its energy? How does a river drop its load? Yes, there is. What is the sequence? The largest and heaviest sediment deposits first. The smallest and lightest sediment deposits last.

Part 2 Quit Landforms and exogenetic processes 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.

Part 2 Quit Landforms and exogenetic processes 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 Sea Pebbles and sand SiltClay

Part 2 Quit Landforms and exogenetic processes

Part 2 Quit Landforms and exogenetic processes The water flowing in a river channel is called ________ flow. What are the other three kinds of water flow? _________ flow, ________ flow and _____ flow. These three kinds of water flow will supply water to the channel flow. channel Overland through base 1Amount of channel water

Part 2 Quit Landforms and exogenetic processes 1Amount of channel water Overland flow Throughflow Base flow Vegetation cover Gradient Drainage density (more / less) rainfall and snowmelt. The amount of channel water increases when there is: (more / less) evaporation. a (larger / smaller) catchment area. (more / less) vegetation cover. a (faster / slower) infiltration rate. a (steeper / gentler) slope gradient. a (lower / higher) drainage density. Rainfall Evaporation Infiltration

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

Part 2 Quit Landforms and exogenetic processes 2Speed of water flow BChannel friction Why does friction affect the speed of water flow? It (prevents / helps) water from flowing downstream. Energy is needed to overcome friction. Lesser energy causes water flows (faster / slower). What factors affect channel friction?

Part 2 Quit Landforms and exogenetic processes (less / more) friction Do you know which channel has a greater speed of flow? Channel AChannel B Channel (A / B) has a shorter wetted perimeter 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: The wetted perimeter of Channel B: aChannel shape The speed of flow becomes (faster / slower) in Channel A. (more / less) energy = 21m 9m + 6m + 6m = 24m 3m + 3m + 18m

Part 2 Quit Landforms and exogenetic processes The _____________ one produces the lowest friction. Look at the three channels shown. They are of the same cross- sectional area. aChannel shape semi-circular aSemi-circular Which shape of channel produces the lowest friction? bSquare cWide and shallow

Part 2 Quit Landforms and exogenetic processes Channel (A / B) has greater friction and lower speed of flow. Same cross-sectional area Channel AChannel B Same cross-sectional area bChannel roughness Channel (A / B) is rougher. The wetted perimeter of Channel (A / B) is longer.

Part 2 Quit Landforms and exogenetic processes The channel becomes less ________. The wearing away of the bed and banks by the _____ carried by a river. Abrasion is the main process in ________ erosion. uneven load Please click above for animation How can a river erode the land? Four ways of fluvial erosion Abrasion vertical

Part 2 Quit Landforms and exogenetic processes The load becomes (larger / smaller) and (rectangular / rounder) downstream. knocks against The load in the river _______________ each other and break down into small pieces. How can a river erode the land? Four ways of fluvial erosion Attrition Please click above for animation

Part 2 Quit Landforms and exogenetic processes The running water is forced into cracks at the banks. The _____________ breaks up the river bed and banks. running water How can a river erode the land? Four ways of fluvial erosion Hydraulic action Please click above for animation The cracks are (enlarged / reduced). Rocks are loosened and removed.

Part 2 Quit Landforms and exogenetic processes For example: ________ in limestone. Water dissolves and removes the _______ minerals from rocks. The rocks are weakened and easily broken up. soluble calcium How can a river erode the land? Four ways of fluvial erosion Corrosion / Solution Please click above for animation