1. R IVER I NVESTIGATION – THE T HEORY !

2. W HAT IS A D RAINAGE B ASIN ? A drainage basin is an area of land drained by a river and its tributaries. Its boundary follows high land around the edge of the basin and is called a watershed or divide. The Rockies in America divide the Mississippi basin from smaller West- flowing rivers.

3. F EATURES OF A D RAINAGE B ASIN

4. COPY THIS DIAGRAM Also label the watershed, and mark with arrows the direction of flow of water towards the river

5. UPPER COURSE YOUTHFUL STAGE

6. UPPER COURSE YOUTHFUL STAGE MIDDLE COURSE MIDDLE AGE STAGE

7. UPPER COURSE YOUTHFUL STAGE MIDDLE COURSE MIDDLE AGE STAGE LOWER COURSE OLD AGE STAGE

8. W HICH PARTS OF THE BASIN ? A B

9. R IVER BASIN CREATION PROCESSES : Weathering Breaking down the rocks Erosion Picking up the rock particles Transport Moving the rock particles Deposition Dropping the rock particles

10. HJULSTROM CURVE

11. T RANSPORTATION Erosion and weathering provide loose material. This material is carried by the river as its load. The load is transported downstream in a number of ways. Suspension Saltation Traction Solution

12. Solution - minerals are dissolved in the water and carried along in solution. Suspension - fine light material is carried along in the water. Traction - large boulders and rocks are rolled along the river bed. Saltation - small pebbles and stones are bounced along the river bed.

13. TERMDEFINITION Abrasion The scouring of the bed and sides of the river by the action of the load itself Load The material transported by a stream or river Hydraulic Action The erosive effect of water without the assistance of rock particles, also involving the force of air Attrition The wearing away of the sediments themselves, making them smaller and rounder Velocity The speed at which the water is travelling downstream Cavitation When tiny bubbles of air implode in fissures and cracks in the channel banks producing shock waves that weaken the banks Solution The chemical action of river water which dissolves carbonate rocks such as limestone, also called corrosion Entrainment The picking up of particles from the bed of the river which are then carried in suspension Unconsolidated rocks Rocks consisting of a loose texture, not cemented together, which are easily eroded.

14. Factors Affecting Rates (or speed) of Erosion LOADVELOCITYGRADIENTGEOLOGYpH HUMAN IMPACT

15. UPPER COURSE Contours close together Steep gradient Significant height difference to sea level Down cutting Water appears fast flowing “noisy” River has a small channel

16. UPPER COURSE FLUVIAL LANDFORMS ( CREATED BY EROSION ) V- shaped valleys Interlocking spurs Waterfalls (breaks in slope) Potholes

17. V SHAPED VALLEYS spur

18. MIDDLE COURSE ( LANDFORMS OF EROSION AND DEPOSITION ). Transition zone from upper course to lower course Slight change in slope gradient Water flowing a bit slower

19. MIDDLE COURSE Rivers starting to flow along a “bendy” route River starting to flow over a wider area (not confined to a v-shaped channel) River bounded by TERRACES, mini-cliffs

21. Friction within the channel bed and banks causes TURBULENT WATER creation of RIFFLES (deposited material) and POOLS (deep water). Water flows FASTEST in the pools and so ERODES and SLOWEST in the riffles and so DEPOSITS.

22. http://www.youtube.com/watch?v=5l4KZ6t69u8&NR=1

23. Erosion (especially hydraulic action of the bank) occurs on the outside of the meander curve. Less water is in contact with the bank, friction is lower, so water velocity is higher. Erosion creates a steep river cliff.

24. Deposition occurs on the inside of the meander curve where depth of water is lowest. As much of the water is in contact with the bank, friction is high, so water velocity is low. The moving water deposits all but the smallest particles that it is transporting. The resulting deposit is called a point bar, slip-off slope or river beach.

25. A MAZON - MEANDERS

26. MEANDERS AND OX BOW LAKES Erosion causes the neck of the meander to become narrower and narrower. Eventually the two outer bends meet and the river cuts through the neck. The water now takes the shortest course rather than flowing round the bend. Deposition gradually seals off the old meander bend which is left isolated from the new channel.

29. O VER TIME OX BOW LAKES MAY FILL UP WITH SEDIMENT AND GRADUALLY DRY UP – THIS IS THEN KNOWN AS A MEANDER SCAR.

30. LOWER COURSE ( LANDFORMS CREATED BY DEPOSITION ) River flowing slowly (not much height difference to SL) Channel is wider but shallower It is only able to carry the finest particles River “wanders” over the land, creating a “bendy” pattern – MEANDERS

31. LOWER COURSE FLUVIAL LANDFORMS Meanders Flood plains Mid channel bars and point bars (see earlier!) River cliffs and terraces and levees Ox bow lakes

32. LOWER COURSE During a flood, water flows over the shallow channel and floods the surrounding land Fine bed load is deposited FLOOD PLAIN Wide flat area (fine particles like clay and silt are very fertile)

34. Farming on the River Niger floodplain

35. F ORMATION OF L EVEES

36. The Bradshaw model describes the characteristics of a river as it progresses from source to mouth. This is the theory behind your investigation. You need to describe what should happen and EXPLAIN why it happens.