Ok 1 (U) notice anything?

1. Ok 1 (U) notice anything? Oh no Jackie Its those First Years again!

2. First year geographyMs Clifford • Rivers: How they shape our land

3. Some important river terms • Source-where a river begins • Course- the route it takes as it flows from an upland area down through its valley until it enters the sea • Tributary- a stream or river which joins a larger river • Confluence- the point at which a tributary joins the river • Mouth- the place where a river enters the sea • Estuary- the part of the mouth that is tidal • River basin- the area that is drained by a river or its tributaries • Watershed- the high ground that separates one river basin from another

4. There are 3 stages in a rivers life • The youthful stage (upper stage) • The mature stage (middle stage) • The old stage (lower stage)

5. 3 stages of a rivers life…just like humans life!

6. The Work of Rivers • The erosional work of streams/rivers carves and shapes the landscape through which they flow. • 3 functions of rivers • Erosion=wearing away the landscape • Transportation=moving the material away (called the rivers load) • Deposition=to drop the load along the way

7. The Work of Rivers RIVERS MAY ERODE IN 4 WAYS: 1. Hydraulic action The force of the flow of the moving water erodes pieces of rock from the banks and bed of the river: this is called Hydraulic Action (This material is called the load)

8. The Work of Rivers 2. Abrasion Load carried by a river will scrape against the soil and rock along the bed and banks of the river, deepening and widening the river channel. This process slowly wears the bed and banks away.

9. The Work of Rivers 3. Attrition When rocks carried by the river rub against each other they are worn down and smoothed.

10. Attrition

11. The Work of Rivers 4. Solution Certain minerals in rocks like limestone can be dissolved by the river

12. The rate of erosion depends on • The size of the river- it erodes faster when it is in flood • The speed of the river- a fast flowing river has more erosive powers • The hardness of the rock- some rocks erode more easily than others

13. How does the river transport its load? • It does this in 4 different ways: • Traction-rolling of stones • Saltation- bouncing of stones • Suspension- carrying of stones • Solution- the load is dissolved

14. 4 ways it transports its load

15. Deposition of a river • This is the dropping of the rivers load

16. The Work of Rivers • Rivers will deposit their load when: • They lose speed • There is a reduction in water in the rivers channel • They flow into a lake or sea • The slope or gradient of the river is reduced

17. The Work of Rivers • A river’s volume decreases when • Dry season • Dry region with high evaporation • Presence of permeable rocks • Receding flood waters

18. The Work of Rivers • A river’s speed decreases when • It enters a lake • It enters a calm sea • It enters a gently sloping plain

19. 3 stages of a river • Youthful stage • Mature stage • Old stage

20. The youthful stage of a river • At this early stage of the river, it flows down a steep gradient. • The river has a small volume • It cuts down into the rock by a process known as vertical erosion • It does this though hydraulic action, abrasion, attrition or solution

21. Features /landforms of the youthful stage • V shaped valley • Interlocking spurs • Potholes • Waterfall

22. Yummy 

23. V Shaped Valley

24. V Shaped Valley • V shaped valley have steep sides and narrow floors. These are formed as the river cuts down into its bed, deepening it by “vertical erosion”. Meanwhile weathering breaks up the soil and rock, weakening the sides of the valley. They eventually collapse and the debris falls into the river. This gives it the v shape

25. Interlocking spurs

26. Interlocking spurs • These are the areas of high ground that jut out like a jig saw from each side of the valley. If the river meets obstacles of hard or resistant rock like granite-it is unable to cut through it. Instead it flows around them but still continues to erode downwards. This is why the river develops a zig-zag course

27. Potholes • Potholes are circular-shaped hollows found on the riverbed. When the riverbed is uneven, the water begins to swirl around. Pebbles that are carried by the swirling water cut down into the riverbed, creating hollows called potholes. This is the process of abrasion. Example: Liffey

28. Waterfalls

29. Waterfalls • A waterfall is a feature where the water flows or falls over a vertical slope. • It develops where a band of hard or resistant rock lies on top of a band of soft rock. The softer rock is eroded by the river more quickly than the hard rock. This causes a plunge pool to be formed by the force of the falling water. • The falling water also cuts under the waterfall to form an over-hang, which eventually collapses. • As this process repeats itself-the river gradually retreats upstream • Examples-Powerscourt, Glencar waterfall or Torc waterfall

30. The mature stage of a river • The river has a greater volume since many tributaries have joined it. It flows over a gentler gradient. • It has a larger load of material to carry now • It flows more slowly than the youthful stage

31. 3 features/landforms of a mature river • Wider valley troughs • Meanders • Flood plain

32. Wider valley troughs • The sides of the mature valley are less steep and the floor is wider and flat • Lateral erosion widens the valley • The river swings from side to side, removing the interlocking spurs • Weathering and mass movement continues so the valley becomes less steep

33. Meanders

34. Meanders • Meanders are curves or loops that develop along the course of a river. • They are formed by both erosion and deposition. • As the river flows around a slight bend, the water on the outside bank flows more quickly and erodes the bank. • The water on the inside flows more slowly . As a result, it deposits its load. • This process continues and the meanders become more pronounced. • Examples include Shannon, Blackwater and the Moy

35. meander

36. Flood Plain

37. Flood plain

38. Floodplain • This is the land on either side of the river. It has a very covering of fertile clay called alluvium. • Following a period of heavy rainfall, the size of a river increases and it may overflow its banks to flood the land. • The water loses its speed and deposits a layer of alluvium

39. Old rivers • This is the last stage of the river and it flows slowly with little energy. It deposits its load because of this lack of energy and because the load is too heavy. • Features found at the old stage include: • Ox Bow lakes • Levees • Deltas

40. Ox Bow Lakes

41. How an OX BOW Lake is formed • An ox bow lake is a horse-shoe shaped lake that was once part of a meander • Erosion takes place on the outer banks of the river and in between the neck of 2 meanders • When the energy has a lot of energy it cuts through the neck to flow along a straight path • The river has little energy so it deposits its load along the channel • This eventually cuts off the meander to form an ox bow lake

42. Ox bow lake

43. Levees

44. levees • Levees are raised banks of alluvium • When a river bursts its banks, it flows over the floodplain • It quickly loses its energy and deposits its heavier load close to the river • Smaller rocks/stones are carried further away • Over time the rocks build up along the river banks to form levees

46. Deltas

47. delta

48. How a delta is formed • A delta is formed when a river is about to enter the sea. • The river loses speed and deposits its load. • Lighter material can be carried out to sea but the heavier load is deposited at the mouth of the river. • Over time the deposited rocks build up forming new land called deltas • The river is split into smaller channels called distributaries • not all rivers flow into the sea so there will be no delta  • `v

49. River mississippi • The mississippi drains nearly 40% of the land surface of the USA • Over time man has interfered with the river in the following ways: • (A) building man made levees to prevent flooding • (B) cutting off meanders so the river flows straighter • THIS HAS EFFECTED THE RIVER IN MANY WAYS: • (a) levees have walls 8 metres high. The river cannot overflow its banks and deposit its load so instead the level of the river increases • The authorities built the levee walls even higher and this means that the river is now higher than the landscape

50. Learning outcome Floods (positives and negatives) Dam building and hydro electric power