Chapter 11. Rivers: Shaping our landscape

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Alexina Baker
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1 Chapter 11 Rivers: Shaping our landscape

2 Learning outcomes In this presentation you will learn: Common terms associated with rivers About the three stages of a river About the processes of river erosion About the processes of river transportation About features formed by river erosion and deposition How human activity affects rivers

3 Common terminology Source Course Confluence Tributary Mouth Drainage basin Watershed Estuary The start of a river The route a river takes The point at which two rivers join together A smaller river that flows into a larger river The end of a river enters the sea Area of land drained by a river Highland surrounding drainage basin Part of river mouth that is tidal Exam hint: You need to understand common terminology associated with rivers.

4 Common terminology Describe each term above.

5 Stages of a river Three stages: Upper or youthful stage Middle or mature stage Lower or old stage Exam hint: You must know the three stages of a river.

6 Stages of a river Upper or youthful stage Steep, fast-flowing Little water Steep, V-shaped valley Narrow, shallow channel High bed load (larger rocks) Features: V-shaped valleys, interlocking spurs, waterfalls Middle or mature stage Starts to slow down More water Still eroding Open, gently sloping valley with flood plain Wider, deeper channel More suspended sediment Features: Meanders, oxbow lakes Lower or old stage Slow-moving river Much more water Depositing, not eroding Open, gently slowing valley with flat and wide flood plain Very wide, deep channel Suspended sediment Features: Flood plains, levees Exam hint: You need to be able to describe a river at each stage.

7 Stages of a river Name two features associated with each stage.

8 The work of rivers Shapes the landscape: Erosion River wears the landscape away Transportation River carries the material it has eroded Deposition River drops off material it was carrying Exam hint: You need to understand how a river shapes the landscape.

River erosion processes Hydraulic action Abrasion Attrition Solution Force of moving water wears away river bed Stones carried by water wear away banks

9 River erosion processes Hydraulic action Abrasion Attrition Solution Force of moving water wears away river bed Stones carried by water wear away banks Stones are worn down as they hit each other Rocks (e.g. limestone) are dissolved by acids in water Exam hint: You need to be able to describe how a river erodes.

10 River transportation Transportation occurs in a number of ways Method depends on: size of material size and speed of river Material transported by river is its load Exam hint: You need to know how a river transports its load.

11 River transportation methods Rolling Bouncing Large stones are rolled along river bed known as traction Smaller pebbles are bounced along river bed known as saltation Suspension Light materials float along in water Solution Materials dissolve and are carried along

12 River deposition Shapes land by leaving sediment in new places Makes new land or adds to existing Causes of deposition: Reduction in river s speed where a river enters a sea or lake or during dry spell Increase in load size when tributary joins or after heavy rain Reduction in river s volume during dry spell When gradient levels off when river reaches flatter land

13 The youthful stage (upper course) River cuts downwards Gradient is steep and river channel narrow Vertical erosion V-shaped valleys Interlocking spurs Waterfalls

V-shaped valleys Steep-sided valley Shape of a V Shaped by vertical erosion River bed made deeper by hydraulic action Mechanical weathering and mass

14 V-shaped valleys Steep-sided valley Shape of a V Shaped by vertical erosion River bed made deeper by hydraulic action Mechanical weathering and mass movement weather sides of valley Examples: upper course of Rivers Liffey, Lee and Moy Exam hint: You must be able to describe how V- shaped valleys are formed.

15 Interlocking spurs Areas of high ground Jut out at both sides of V- shaped valley River winds and bends around hard rock as it erodes Still erodes vertically Creates interlocking spurs Example: Upper course of Rivers Barrow and Slaney Exam hint: You must be able to describe how interlocking spurs are formed.

16 Waterfalls Vertical drop in course of river youthful stage Band of hard rock across band of soft rock Soft rock eroded quicker drop is created Material creates a plunge pool at base Enlarges over time Hydraulic action and abrasion cause undercutting Creates overhang eventually collapses This is repeated and waterfall retreats over time Exam hint: You need to know how waves are formed.

17 Waterfalls Name another example of a waterfall.

18 The mature stage (middle course) River has more energy Higher volume of water Tributaries or other rivers have joined Gradient is gentle Lateral erosion has widened river channel River channel has deepened River carrying more material

Meanders Curves or bends River erodes laterally Right then left Forms large bends Horseshoe-like loops Meanders formed by deposition and erosion Hydraulic action

19 Meanders Curves or bends River erodes laterally Right then left Forms large bends Horseshoe-like loops Meanders formed by deposition and erosion Hydraulic action erodes outside of bend Material deposited on inside of bend Example: Middle course of River Shannon Exam hint: You must be able to describe how meanders are formed.

20 Oxbow lakes Horseshoe-shaped lake Meander cut off from river Neck of meander becomes tight During flood more discharge River breaks through Loop cut off sediment dropped at entrance Forms oxbow lake Dries up oxbow scar Examples: River Liffey and River Moy Exam hint: You must be able to describe how oxbow lakes are formed.

21 Oxbow lakes

22 The old stage (lower course) Slow-moving river Much more water Deposition, not erosion Gently sloping valley Very wide and very deep channel

23 Flood plains Wide, flat area of land either side of river River nearing sea, deposition main process Large amount of sediment alluvium River spread out during flood and deposits load Makes land fertile Highest point reached bluff line Exam hint: You must be able to describe flood plains and their features.

24 Flood plain Examples: Lower course of River Moy and River Liffey

Levees Build up of alluvium on banks of river Caused by floods Low flow materials deposited on river bed Flood water leaves channel and deposits heavier material on banks After many

25 Levees Build up of alluvium on banks of river Caused by floods Low flow materials deposited on river bed Flood water leaves channel and deposits heavier material on banks After many floods river bank builds on both sides Examples: Mature stage of Rivers Liffey and Moy Exam hint: You need to know how waves are formed. What are artificial levees and what are they used for?

26 Deltas Triangular/ fan-shaped at mouth of river Features of deposition old stage River mouth choked with sediment River channel splits into smaller channels Form under certain conditions: Transporting large amount of sediment Sea small tidal range, weak currents Shallow at mouth of river Examples: Mississippi River in USA and the Nile delta in Africa Exam hint: You need to know how waves are formed.

27 Human activities and rivers Humans use rivers in variety of ways Interactions can be beneficial or harmful Interactions include: Transport Tourism Fishing Settlement Pollution Flooding Hydroelectric power (HEP)

28 Human activities and rivers Transport Tourism Fishing Used to transport people and goods, e.g. Limerick has port function, River Rhine is important transport route in Europe Use rivers for cruising and fishing, e.g. Carrick-on-Shannon and Athlone on River Shannon are tourist destinations Popular with anglers, many popular for salmon fishing, e.g. River Moy Settlement Settlement along river banks provides food, water and transport Pollution Flooding HEP Farming spread slurry; domestic waste material from septic tanks; industrial factories dump waste Cutting down trees surface run-off and erosion, can lead to deposition, river rises and bursts banks HEP stations built using dams, large concrete wall to control flow of river, can have both positive and negative impact Exam hint: You need to be able to describe how human interactions impact on rivers.

29 HEP: positive and negative aspects Positive aspects Generate cheap, clean, renewable electricity Water builds up in reservoir water supply Reservoir can be used for leisure activities fishing and water sports Negative aspects Creation of reservoir can lose agricultural land Families need to be relocated New roads and bridges have to be built Fish stocks can be affected Exam hint: You may be asked to discuss the positive and negative aspects of HEP.

30 Inniscarra, Co. Cork Location: Inniscarra and Carrigadrohid Technology: Hydro Capacity: 27 MW Commissioned: 1957 Part of Lee Hydroelectric Scheme Located west of Ballincollig Buttress dam, 44 m Parts of Lee valley flooded to create reservoirs Inniscarra 530 h (5 km²) 40 k of bank can be fished Exam hint: You need to be able to describe a HEP scheme you have studied.

31 Sample answer i) Rivers are often used to generate hydroelectric power. Describe one positive and one negative effect of a HEP scheme you have studied. Answer: Positive Inniscarra reservoir is used for angling. Negative Agricultural land was lost when the Lee valley was flooded to create reservoirs for generating electricity.

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