Lesley Monk Balfron High School Session 2005/6

1. HYDROSPHERE 3 Lesley Monk Balfron High School Session 2005/6

2. HYDROSPHERE 3 STUDYING RIVER VALLEYS • We will look at;- • General characteristics of rivers. • Upper stages- waterfalls. • Middle stages- meanders and oxbow lakes. • Lower stages – levees and deltas • Rejuvenation At Standard Grade, you learned about the three stages of a typical river, and about the characteristics of each stage. We will be re-visiting this material and adding more depth- excuse the pun- to our studies of rivers. These slide-shows are all on the Prepwork folder if you wish to copy any notes from them; we will not be stopping in class for you to do this

3. HYDROSPHERE 3 6 GENERAL CHARACTERISTICS A river LONG PROFILE is a sideways look at a river valley from source to mouth. It can also be called a LONG SECTION. In an ideal river, it looks like this;- Notice the three stages we studied in S4.

4. HYDROSPHERE 3 The key to understanding how a river creates its landforms is to look at the energy needed to move the material around it. Large sized material needs high energy. Large amounts of material needs high energy. Tiny particles need only low amounts of energy. Small amounts of material need little energy.

5. HYDROSPHERE 3 Where does the energy come from? • The volume of water, which varies with precipitation. • The speed of the flow, which varies with gradient of the river bed.

6. HYDROSPHERE 3 7 As the diagram on the handout shows, energy values determine whether the river erodes, transports or deposits a particle. (Note the scale isn’t the more familiar cumecs- cubic metres per second- but a more sensitive mms per second! ) This means that you can predict for any river in any conditions how the river will deal with material at a given speed- “discharge”.

7. HYDROSPHERE 3 So it is obvious that erosion is greatest in the upper stage and deposition in the lower stage. EROSION DEPOSITION SOURCE MOUTH

8. HYDROSPHERE 3 THINK ENERGY! TRANSPORT TYPES Make a copy of the diagram at the foot of page 262 of Wider World. This shows the four main methods that a river uses to move material of different sizes.

9. HYDROSPHERE 3 UPPER STAGES- WATERFALLS 3. Why does the rock layer collapse? Study factzone 10 about this in the booklet. Answer the questions. 4. What two-word landform is created by these processes? 1. Describe simply the rock-type layout of a typical waterfall. 5. Name and locate two examples of this feature. 2. Describe where and how the plunge pool is created.

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11. HYDROSPHERE 3 ANSWERS 1.A layer of hard rock lies over softer rock. 3. The rock layer collapses as a result of the weight of the hard rock and gravity. 2.The plunge pool is created by water eroding vertically and laterally below the hard rock. 4.This creates a river gorge. 5.Thornton Force on the River Twiss, Ingleton. High Force on the River Tees.(examples only! )

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13. HYDROSPHERE 3 MIDDLE STAGES- MEANDERS These are found initially in the middle stage, although they get well developed in the lower stage too. There are a few new terms about meanders for you to learn, beyond the Standard Grade ones. Read section 11 in the booklet and use the diagram on page 19 to help define;- SINUOSITY WAVELENGTH POINTS OF INFLEXION

14. HYDROSPHERE 3 The first stages in the formation of meanders is believed to be the development of ‘riffles and pools’. These are zones of alternating deposition and erosion that cause the channel of the river to alter course, thus creating the meander.

15. HYDROSPHERE 3 8 Meanders should be familiar to you from Standard Grade, and their features are shown as a reminder on the handout diagram. Use Wider World page 284 to label and colour your handout, and stick it into your jotter. Can you identify each feature lettered ?

16. HYDROSPHERE 3 Remember that meanders are a developing feature, changing with time and moving both across the flood plain and down-stream! Remind yourself how they do this- what are the PROCESSES?

17. HYDROSPHERE 3 The photograph here and the diagram on the next slide shows the processes going on below the water. Notice how the inner bank is being built up into a point bar deposit /river beach/ slip-off slope, and the outer bank is being eroded into a river cliff.

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19. HYDROSPHERE 3 A B The finale of the process is for an ox-bow lake to form. Read the notes in the booklet page 22 and look at the diagrams here.

20. HYDROSPHERE 3 An ox-bow lake on the Endrick valley floodplain.

21. HYDROSPHERE 3 The meanders and ox-bow lakes of the Mississippi River from the air.

22. HYDROSPHERE 3 The movement of the meanders create the wide floodplain and bluffs of the mature lower stage of the river.

23. HYDROSPHERE 3 LOWER STAGE Here the gradient is low and energy levels are also low. As a result……….. ……there is much deposition and high sinuosity; the flood plain is wide.

24. HYDROSPHERE 3 9 LEVEES Levees are either natural or man-made raised banks. Read about them in the booklet, page 23. You need to be able to explain them as well as this in an answer!

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26. HYDROSPHERE 3 Read also the sections about BRAIDING and DELTAS. Answer the following questions firstly about BRAIDING. 1.Why are there sometimes greater than usual amounts of load in the channel? 2. What causes this load to be deposited? 3. Explain why these mounds of material are unstable?

27. HYDROSPHERE 3 ANSWERS 1. Increased discharge in the river will bring down more (and larger) load from upstream. 2. If the discharge drops quickly, reducing the volume in the channel, the material will be dropped in the bed. Sometimes debris remains long enough to be colonised with vegetation which stabilises it more! 3. The material is poorly consolidated and is likely to be re-eroded with further increased discharge.

28. HYDROSPHERE 3 Answer these DELTA questions;- 1.Why does a delta not form if there are tides or currents? 2. Why are the beds/ sets graded by size? 3. Why do distributaries form? 4. Name a big river in Europe that has a delta. Say where it is.

29. HYDROSPHERE 3 ANSWERS 1. Currents would wash away the deposits before they could gather. 2. As the material reaches the still water, the river flow almost stops. The heavier material drops and rolls down the slope offshore, and the medium particles fall on top of them. The lightest particles are carried further out to sea and deposited, to be covered much later by more heavy deposits. 3. Distributaries form as the water has trouble flowing over the deposited material. 4.The Rhine delta is in Netherlands at Rotterdam, and the Rhone delta is in France, beside Marseilles.

30. HYDROSPHERE 3 10 11 12 Summary-handouts

31. HYDROSPHERE 3 REJUVENATION This is the name given to when a river gets a new rush of energy. This is due to ISOSTATIC UPLIFT- remember what that is? This is when the land rises up after the weight of the glaciers has been removed. It is seldom even across the land.

32. HYDROSPHERE 3 As the land rises, there is now more falling for the river to do to get to sea- level. It starts to flow faster with the renewed energy, and vertical erosion starts to increase. The results are the channel of the river eats downwards into the floodplain and creates river terraces and incised/ entrenched meanders. Now watch video 86 number 3, second half

33. HYDROSPHERE 3 THIS IS THE END OF THIS TOPIC. YOU NOW ONLY NEED TO LEARN THIS TOPIC FOR THE EXAM AND THE NAB!