3.  Potholes are formed due to stream or river erosion which initiates by simple plucking out at the riverbed by hydraulic action.  These are variously shaped depressions of different dimensions generally cylindrical or bowl shaped in outline and range from a few centimeters to many meters in diameters as well as in depth.  Some of the depressions are formed when pebbles and gravels of stronger rocks are caught in eddies giving rise to swirling and churning motion.

5. A valley may be defined as a low land surrounded on sides by inclined hill slopes and mountains. Every major river is associated with a valley of its own.

7.  When a valley continuously undergoes deepening due process of river erosion: hydraulic action,abrasion and chemical action or corrosion gives rise to gorges and canyons.  A canyon is a specific type of gorge formed essentially in stratified and horizontal rock types.  The Grand Canyon of Colorado is deepest canyon in world: depth varies from 900 to 1800 meters. width from 60 to 90 meters and length of 300 km.  All the Himalayan Rivers and especially the Indus and the Chenab have developed numerous gorges in their inner and middle Himalayan courses

9. Buttes are formed by erosion when hard caprock covers a layer of softer rock that is eventually worn away. erosioncaprockrock Large side caps are called mesa.

11.  It is defined as magnificent jumps made by river water at certain specific parts of their course where there is a sudden and considerable drop in the gradient of the channel.  In waterfall, the river literally falls (instated of flowing) from a considerable height before acquiring normal flow again at a lower level.  Velocity of water at the point of fall increases tremendously.

14. Erosion is still an important process. The river is now flowing over flatter land and so the dominant direction of erosion is lateral (from side to side). The river has a greater discharge and so has more energy to transport material. Material that is transported by a river is called its load. Deposition is also an important process and occurs when the velocity of the river decreases or if the discharge falls due to a dry spell of weather. Processes operating in the middle course of a river

15. Meanders Oxbow Lakes DEPOSITION and EROSION create these landforms What landforms are found in the middle course?

16. Meanders 1 2 3

17. Floodplain Deposits on the inner meander bend where there is low energy Erosion on the outer bend where there is faster flow. It creates a river cliff Slip-Off Slope Direction of meander migration

18. Formation of Meanders

19. Point bar deposits

20. Point Bar Deposits Point bar deposits grows laterally through time

21. Cut bank erosion Point bar deposits } Meander loop

22. Erosion of a Cutbank

23. Formation of an Oxbow

25. Meanders and Oxbow Lake Green River, Wyoming

26. Mississippi Meanders

27. Meandering stream flowing from top of screen to bottom

28. Maximum erosion Maximum deposition

35. Oxbow Lake Oxbow cuttoff Meander scars

36. Animation #83: Stream Processes – Floodplain Development and Oxbow Lakes

37. Ox Bow Lake Formation Can you look at the diagram & explain the formation of ox-bow lakes?

38. Ox Bow lake on Mississippi

41. The Lower Course of a River Formation of a flood plain, levees, delta and estuary.

42. Floodplains, Deltas and Levees. The pictures below show a floodplain, a delta and levees. Using your prior knowledge of river processes come up with a theory to explain how they are formed. The key words underneath each picture will help. deposition Slow flow alluvium (silt) flood flat deposition slow sea/lake load channel blocked deposit flood large load smaller load Main Channel Levee Sea/lake Floodplain

43. Defintions Flood plains A flood plain is the wide, flat area of land on either side of the river in its middle and lower course. Levees Levees are natural embankments of silt along the banks of a river, which are often several metres higher than the flood plain.

44. Levee formation

45. Animation #81: Stream Processes – Floodplain Development

46. Delta Formation Deltas form at the mouths of many of the world’s larger rivers, e.g the Nile (Egypt), the Ganges (Bangladesh), the Mississippi (USA). A delta is a flat area of sand and silt built into the sea. It is formed by deposition. 1.When a river enters a sea or lake carrying large volumes of fine material, the velocity slows and causes the load to be deposited in layers. 2.Over time, the deposited material blocks channels and forms small islands separated by river channels called distributaries.

47. Delta Shapes Fan DeltaBird-Foot Delta

48. The Drainage Systems of Youthful Streams End at the Base of the Mountains Where Alluvial Fans are Deposited.

49. Alluvial Fans – When high-gradient streams emerge from the narrow valley of a mountain front, they often deposit some of this sediment forming alluvial fans. Due to a dramatic decrease in velocity. Causing Sediment to drop out of suspension. Slopes outward in a broad arc similar to a delta. Alluvial Fans Transition from Drainage to Transport Systems

50. Drainage Patterns Pattern of the interconnected network of streams in an area –Common drainage patterns Dendritic Radial Rectangular Trellis

51. Drainage Patterns Figure 16.32