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Channel processes and features Valley slope processes and landforms RIVER STUDIES.

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Presentation on theme: "Channel processes and features Valley slope processes and landforms RIVER STUDIES."— Presentation transcript:

1 Channel processes and features Valley slope processes and landforms RIVER STUDIES

2 Satellite view of river drainage, Middle East

3 Microscale drainage basin

4 Upper valley characteristics

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6 “V”shape valley, vertical erosion dominant

7 Upper valley characteristics “V”shape valley, vertical erosion dominant Interlocking spurs

8 Upper valley characteristics “V”shape valley, vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes

9 Upper valley characteristics “V”shape valley, vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes Terracettes formed by soil creep

10 Upper valley characteristics “V”shape valley, vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes Terracettes formed by soil creep Narrow, shallow channel, low velocity and discharge

11 Upper valley characteristics “V”shape valley, vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes Terracettes formed by soil creep Narrow, shallow channel, low velocity and discharge Large bedload derived from upstream and from valley sides

12 Interlocking spurs, Robinson, Lake District A typical upper course valley with interlocking spurs, steep valley sides and active slope processes

13 Choked runnel, N. Pennines Ephemeral stream or runnel - water present only during high rainfall events

14 Choked runnel, N. Pennines Debris brought downslope towards channel - dropped when water disappears after storm Ephemeral stream or runnel - water present only during high rainfall events

15 Choked runnel, N. Pennines Debris brought downslope towards channel - dropped when water disappears after storm Ephemeral stream or runnel- water present only during high rainfall events Vertical erosion creating steep, bare slopes vulnerable to further erosion - an example of positive feedback in a slope system

16 River load in upper course Load is dumped in summer due to the low discharge unable to carry the c________ and c__________ of load at higher flow levels

17 River load in upper course Load is dumped in summer due to the low discharge unable to carry the capacity and competence of load at higher flow levels

18 River load in upper course Load is dumped in summer due to the low discharge unable to carry the capacity and competence of load at higher flow levels

19 River load in upper course Boulders are large and semi-rounded, due to attrition within the load and abrasion with the stream bed and banks Load is dumped in summer due to the low discharge unable to carry the capacity and competence of load at higher flow levels

20 Rapids in the Upper Tees Valley

21 Rapids are mini- waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded

22 Rapids in the Upper Tees Valley Rapids are mini- waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded Shallow, slow flowing river due to large amount of friction.

23 Rapids in the Upper Tees Valley Rapids are mini- waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded Shallow, slow flowing river due to large amount of friction. Wetted perimeter is large compared to cross sectional area of water - resulting in a low ????????????

24 Rapids in the Upper Tees Valley Rapids are mini- waterfalls Protruding bands of more resistant strata create steps over which rapids fall - the river bed is ungraded Shallow, slow flowing river due to large amount of friction. Wetted perimeter is large compared to cross sectional area of water - resulting in a low hydraulic radius (low efficiency)

25 High Force waterfall, R. Tees

26 Huge step in river bed due to igneous intrusion of dolerite into the limestone.

27 High Force waterfall, R. Tees Huge step in river bed due to igneous intrusion of dolerite into the limestone. Plunge pool where the dolerite wall is undercut, causing rockfalls and recession of the waterfall upstream

28 High Force waterfall, R. Tees Huge step in river bed due to igneous intrusion of dolerite into the limestone. Waterfall creates gorge as it recedes upstream by eroding the base and neck Plunge pool where the dolerite wall is undercut, causing rockfalls and recession of the waterfall upstream

29 High Force waterfall, R. Tees Huge step in river bed due to igneous intrusion of dolerite into the limestone. The long profile will be graded over time Waterfall creates gorge as it recedes upstream by eroding the base and neck Plunge pool where the dolerite wall is undercut, causing rockfalls and recession of the waterfall upstream

30 Headward erosion, Offa’s Dyke This is amazing!!

31 Headward erosion, Offa’s Dyke Spring erodes ground over which it flows and lubricates base of cliff, causing slumping and headward erosion

32 Headward erosion, R. Colorado

33 River seeps out from spring at base and undermines steep cliff, causing rockfalls and headwall recession

34 Headward erosion, R. Colorado Rivers erode in a headward direction, eating back into plateau River seeps out from spring at base and undermines steep cliff, causing rockfalls and headwall recession

35 Potholes in R. Wharfe Smooth sculpturing of rock by abrasion, showing evidence of water levels during high discharge events Vertical erosion is dominant

36 Close-up of potholes

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38 Circular potholes due to eddying motion when river energy is high

39 Close-up of potholes Circular potholes due to eddying motion when river energy is high Potholes will join together by abrasion, and deepen by vertical erosion

40 Close-up of potholes Circular potholes due to eddying motion when river energy is high Load is picked up and used to scour or abrade pothole. Load itself becomes rounded by attrition Potholes will join together by abrasion, and deepen by vertical erosion

41 Potholes, human scale!!

42 Middle course, R. Tees

43 Valley opens out, more gentle slopes, wider valley bottom

44 Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders

45 Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders Floodplain

46 Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders Floodplain River channel wider, deeper, greater velocity and discharge

47 Meander, R. Lavant, Chichester

48 Floodplain

49 Meander, R. Lavant, Chichester Floodplain Point bar deposits on the inner meander bend where there is low energy

50 Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff, caused by concentrated erosion due to the Point bar deposits on the inner meander bend where there is low energy

51 Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff, caused by concentrated erosion due to the thalweg Point bar deposits on the inner meander bend where there is low energy

52 Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff, caused by concentrated erosion due to the thalweg and Point bar deposits on the inner meander bend where there is low energy helicoidal flow

53 Meander, R. Lavant, Chichester Floodplain Steep bank known as the river bluff or cliff, caused by concentrated erosion due to the thalweg and Point bar deposits on the inner meander bend where there is low energy helicoidal flow pool riffl e pool Pools develop at meander bends and riffles in the stretches between bends

54 Meander on the R. Colorado

55 Meander incised into plateau due to rejuvenation

56 Meander on the R. Colorado Meander incised into plateau due to rejuvenation Different strata show evidence of past climates or hydrological events

57 Meander on the R. Colorado Meander incised into plateau due to rejuvenation Different strata show evidence of past climates or hydrological events. Stratum with large boulders must have formed in wetter conditions when higher river discharge carried a greater competence of load

58 Migrating meanders, R. Gongola, Nigeria

59 Former course marked by white sediments Current channel is braided

60 Lower Severn Valley

61 Well developed meanders with bars in the channel indicating high sediment load Very wide floodplain Very gentle valley side gradients

62 River terraces, R. Agri, S. Italy

63 River has been rejuvenated causing renewed vertical erosion - base level has dropped either due to rising land or falling sealevel

64 River terraces, R. Agri, S. Italy Flat terraces represent former floodplains River has been rejuvenated causing renewed vertical erosion - base level has dropped either due to rising land or falling sealevel

65 Flooding in the Severn Valley

66 Floodplain can be mapped into risk zones high to low

67 Flooding in the Severn Valley Floodplain can be mapped into risk zones high to low Floods can be beneficial - they renew soil fertility by depositing sediment on floodplain

68 Flooding in the Severn Valley Floodplain can be mapped into risk zones high to low Floods can be beneficial - they renew soil fertility by depositing sediment on floodplain Floods result in large amounts of sediment transported in the channel

69 Padstow estuary Estuaries are tidal, dominated by marine sediments At low tide, mudflats are exposed

70 Alluvial fan, Buttermere, Lake District

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72 Lake Buttermere acts as a local baselevel for the stream, leading to deposition of load in a triangular shape - an alluvial fan This is the same process that forms major deltas at the coast e.g. R. Nile

73 Braided river, Swiss Alps

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75 Daytime snowmelt in summer produces flashy regime Vast amounts of sediment supplied from frost- shattered valley sides

76 Braided river, Swiss Alps Daytime snowmelt in summer produces flashy regime Vast amounts of sediment supplied from frost- shattered valley sides Channel course can change daily due to changes in discharge and loose sediments

77 Summary of channel characteristics (1) Processes

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81 Summary of channel characteristics (2) Landforms

82 Rapids Waterfal l Pothole

83 Summary of channel characteristics (2) Landforms Rapids Waterfal l Pothole Meander Bluff/cliff Point bar Pool Riffle

84 Summary of channel characteristics (2) Landforms Rapids Waterfal l Pothole Meander Bluff/cliff Point bar Pool Riffle Knick point Braids Alluvial fan Delta

85 Summary of channel characteristics (3) Concepts and technical terms

86 Discharge Regime - flashy - regular Capacity Competence

87 Summary of channel characteristics (3) Concepts and technical terms Discharge Regime - flashy - regular Capacity Competence Hydraulic radius - cross sectional area - wetted perimeter

88 Summary of channel characteristics (3) Concepts and technical terms Discharge Regime - flashy - regular Capacity Competence Hydraulic radius - cross sectional area - wetted perimeter Long profile Graded profile Rejuvenation Base level

89 Summary of channel characteristics (3) Concepts and technical terms Discharge Regime - flashy - regular Capacity Competence Hydraulic radius - cross sectional area - wetted perimeter Long profile Graded profile Rejuvenation Base level Thalweg Helicoidal flow Meander migration

90 Summary of valley characteristics

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