Rivers

2. 10.0 Rivers

3. 10.1 The Journey of a River The journey a river takes from its source to the sea.

4. 10.2 The Stages of a River The journey a river takes from its source to its mouth is called the course of the river. This course is broken up into three different stages. Lower Course Upper Course Middle Course

5. 10.2 The Stages of a River V-shaped valley Meanders Ox-bow lakes Interlocking spurs Waterfalls Wide valleys Flood plains Deltas Levees

6. 10.3 The Processes of a River River Erosion 1 2 4 3

7. 10.3 The Processes of a River River Transportation As a river moves from source to the sea, it transports its load. The load is transported in a number of ways by the river. 4 3 1 2 Large pebbles and stones are rolled and dragged along the river bed by the force of the water. This method is known as traction. 1

8. 10.3 The Processes of a River River Transportation As a river moves from source to the sea, it transports its load. The load is transported in a number of ways by the river. 4 3 1 2 2 Small pebbles are bounced along the river bed. This method is known as saltation.

9. 10.3 The Processes of a River River Transportation As a river moves from source to the sea, it transports its load. The load is transported in a number of ways by the river. 4 3 1 2 Tiny particles are held in suspension in the water – the movement of water is fast enough to keep them from dropping to the river bed. 3

10. 10.3 The Processes of a River River Transportation As a river moves from source to the sea, it transports its load. The load is transported in a number of ways by the river. 4 3 1 2 4 Dissolved minerals like limestone is carried in solution – it cannot be seen.

11. 10.3 The Processes of a River River Deposition Rivers deposit their load when they begin to slow down and lose energy. This happens: when a river reaches flat ground when a river enters a lake or the sea at the inside bend of a meander. River deposition

12. 10.4 Landforms of a Youthful River V-Shaped Valley When a river is in its youthful stage, it erodes vertically (downwards). This forms a valley with steep sides and a narrow floor. V-shaped valleys are a feature of erosion in a river. An example can be seen in the youthful stage of the River Liffey. The valley is called V-shaped as it looks like the letter V. Gap of Dunloe, Co. Kerry

13. 10.4 Landforms of a Youthful River V-Shaped Valley – Formation V-Shaped valley

14. 10.4 Landforms of a Youthful River Interlocking Spurs are areas of high ground that jut out on either side of the river and appear to lock together. Interlocking spurs

15. 10.4 Landforms of a Youthful River Waterfalls Waterfalls are a feature of erosion. An example of a waterfall can be seen at Powerscourt, Co. Wicklow. A waterfall occurs where a river flows over a vertical slope. Powerscourt, Co. Wicklow

16. 10.4 Landforms of a Youthful River Waterfalls – Formation 1 1 1 River flows over an area where hard rock lies on top of an area of soft rock. 2 3 4 Waterfall

17. 10.4 Landforms of a Youthful River Waterfalls – Formation 1 2 2 2 The river erodes the soft rock faster. This develops a vertical drop where the hard rock and soft rock meet. This drop is called a waterfall. 3 4 Waterfall

18. 10.4 Landforms of a Youthful River Waterfalls – Formation 1 3 2 At the base, a plunge pool develops due to the force of the falling water, along with its load swirling around at the base, which wears away the base by abrasion. 3 3 4 Waterfall

19. 10.4 Landforms of a Youthful River Waterfalls – Formation 1 4 2 The rock above the plunge pool is undercut and left hanging. It eventually collapses into the plunge pool below. As this process continues, the waterfall slowly erodes its way upstream. 3 4 4 Waterfall

20. 10.5 Landforms of a Mature River Wide Valley Interlocking spurs have been removed by lateral erosion, which widens the valley floor. Weathering and mass movement have also made the valley sides less steep. This creates a wide river valley that is not very steep. In the mature stage of a river, erosion occurs laterally (sideways) rather than vertically (downwards). Wide valley Wide valley

21. 10.5 Landforms of a Mature River Flood Plains This rich and fertile soil is full of minerals and so is excellent for farming. A flood plain is an area of flat land on either side of the river channel found in the mature and old stages of a river. Flood plains are covered in fertile soil, known as alluvium.

22. 10.5 Landforms of a Mature River Meanders Meanders are formed by a combination of erosion and deposition in the mature and old age stages of a river. An example of a meander can be seen in the middle and lower course of the Rivers Shannon and Boyne. Meander

23. 10.5 Landforms of a Mature River Meanders – Formation 1 Water flows more quickly on the outside of the river bend. The river erodes the bend by a combination of hydraulic action and abrasion.

24. 10.5 Landforms of a Mature River Meanders – Formation 2 Water flows more slowly on the inside bend of the river. Material is deposited on the inside bend as the river loses energy here.

25. 10.6 Landforms of an Old River Levees A levee is a build-up of alluvium on the banks of a river and is a feature of the old stageriver. Levees are caused by floods and are a feature of deposition. Fun Fact! Levees can be seen in the lower course of the River Liffey and the River Moy, Co. Mayo.

26. 10.6 Landforms of an Old River Levees – Formation During times of low flow in a river, the load that is being carried by the river is dropped onto the river bed. This raises the height of the bed. 1

27. 10.6 Landforms of an Old River Levees – Formation During times of flood, the water flows out more easily over the top of the channel and onto the surrounding land. As it does this, it loses energy and deposits its load. 2

28. 10.6 Landforms of an Old River Levees – Formation The heavy coarse material is deposited on the river banks. The finer silt is deposited further away onto the flood plain. 3

29. 10.6 Landforms of an Old River Levees – Formation 4 After many floods, the river builds up a bank on either side.

30. 10.6 Landforms of an Old River Ox-Bow Lakes Ox-bow lakes are horseshoe-shaped lakes found on the flood plains of old rivers. They are formed by river erosion and deposition. An example can be seen on the River Moy.

31. 10.6 Landforms of an Old River Ox-Bow Lakes – Formation 2 3 1 Erosion by hydraulic action and abrasion takes place on the outside bank of the meander. The neck of land between the meander begins to narrow. 1

32. 10.6 Landforms of an Old River Ox-Bow Lakes – Formation 2 3 1 During times of flood, the water has increased energy. It takes the shortest course by breaking through the neck and begins to flow in a new, more direct course. 2

33. 10.6 Landforms of an Old River Ox-Bow Lakes – Formation 2 3 1 Deposits of alluvium now build up and seal off both ends of the meander. The old section of the meander is now cut off from the main river and becomes known as an ox-bow lake. Over time, the lake may dry up. 3

34. 10.6 Landforms of an Old River Delta A delta is a fan-shaped area of land found at the mouth of a river. It is a feature of river deposition. Delta

35. 10.6 Landforms of an Old River Delta – Formation 1 When a river reaches a lake or the sea, it slows down and loses the power to carry sediment.

36. 10.6 Landforms of an Old River Delta – Formation 2 The sediment is then dropped at the mouth of the river. Some rivers drop so much sediment that waves and tides can’t carry it all away. This forms the delta.

37. 10.6 Landforms of an Old River Delta – Formation 3 The large deposits build up over time at the mouth of the river and block the river’s entry to the sea. The river then has to break through the delta in many small channels called distributaries.

38. 10.7 Rivers and Human Interaction Case Study: Flooding in Mallow A ‘Flood Relief Scheme’ for Mallow was planned. The aim of the relief scheme was to try to prevent serious damage to local homes and businesses from flooding. Records as far back as 1628 detail damage to structures in the town from flooding. The town of Mallow in Co. Cork has a long history of flooding from the River Blackwater.

39. 10.7 Rivers and Human Interaction Case Study: Flooding in Mallow

40. 10.7 Rivers and Human Interaction Case Study: Flooding in Mallow • Reduction in: • damage to homes and businesses • stress and anxiety experienced by local people from the threat of future flooding • financial loss to local businesses • disruption to the local community • Built flood defences: • flood defence walls • storm drains • pumping stations Provided protection against a one-in-one-hundred-years flood event Designed and constructed all defence walls with future climate change in mind Developed a flood warning system for the people of Mallow

41. 10.7 Rivers and Human Interaction Case Study: Flooding in Mallow A

42. 10.7 Rivers and Human Interaction Case Study: Flooding in Mallow B

43. 10.7 Rivers and Human Interaction Case Study: Flooding in Mallow C

44. 10.7 Rivers and Human Interaction Case Study: Flooding in Mallow D

45. Video: Waterfalls, Rivers and Floods