River Erosion and its Associated fetures

River Erosion, River Transportation, River Deposition and Various Deposition of Land-forms

1. River Erosion & its Associated Features Dr. V . R Ghodake Department of Civil Engineering. Sinhgad College Of Engineering, Vadgaon (Bk), Pune. Email Id- [email protected] Mobile- [phone]

2. Longitudinal River Profile Elevation (feet) 3,000 Headwaters Ultimate Base level River Length (Miles) 100 Steep, high-gradient gentle, low-gradient This diagram outlines the longitudinal profile of a river basin from the headwaters to the ultimate base level, or sea level. A rivers gradient is steepest near the headwaters and gentlest near the base level. In South Carolina, the steepest sections are often found in the blue Ridge and Piedmont, while the gentler gradient occurs in the Coastal Plain. River length, or distance, is measured from the rivers mouth to its headwaters, seemingly reversed from what one might expect. Longitudinal Profile and Watersheds Headwaters: multiple low-order streams near drainage divide Base level: single outflow and highest order stream This figure is a hypothetical river basin. The black dotted line represents the drainage divide and the numbers refer to stream order. Any rainfall that falls within the black dotted line will eventually flow into the main strem river and out at the mouth. Stream order increases from the headwaters to the base level. In this example, the river is a5 th -order river. Stream Order: 1 st order and 1 st order = 2 nd order 2 nd order and 2 nd order = 3 rd order 3 rd order and 3 rd order = 4 th order 4 th order and 4 th order = 5 th order And so on, 5 and 5 =6, 6 and 6 =7 th order… 5 1 1 1 2 2 1 1 3 4 3 4 5

3. 3 Table of Contents Rivers and Basins

4. Radial type Drainage Pattern

5. Radial Drainage pattern

6. Dendritic type Drainage Pattern

7. – Trellis type Drainage Pattern

8. Rectangular type Drainage Pattern

9. Common River Features

10. A river can erode material from its bed and banks in 4 main ways Chemical Action Abrasion Hydraulic Action Attrition

11. The Work of Rivers The erosional work of streams/rivers and shapes the landscape through which they flow. functions of rivers Erosion Transportation Deposition

12. The Work of Rivers Erosion A river may erode in 4 ways Abrasion/corrasion Load carried by a river will grind against its bed and sides. This process slowly wears the bed and sides away.

13. The Work of Rivers 2 . Attrition When thrown against the sides and bed of rivers, the load gets broken into smaller pieces.

14. The Work of Rivers 3 . Hydraulic action The work of turbulence in the water. Running water causes friction in the joints of rocks in a stream channel Joints may be enlarged

15. The Work of Rivers 4 . Solution/Corrosion Certain minerals in rocks like limestone can be dissolved in water. Rocks are then eroded.

16. Methods of Transportation Rivers transport material in 3 main ways Solutio - Some minerals (particularly in limestone areas) dissolve easily in water and are not visible to the naked eye Suspension- As the speed or velocity of a river increases, it is able to pick up and carry larger and larger particles in its flow. Where particles are carried along in the flow and are not in contact with the river bed, they are said to be travelling in suspension. Bed load- heavy bigger rock fragments moves along with the flow of water is known as bed load.

17. Methods of Transportation Siltation - Heavier particles may not be held in the flow all the time but may be bounced along the bed Traction - The heaviest particles are rolled along the bed. Such particles may only be moved when the river has a large volume of water in it

18. 21 Boulders are large and semi-rounded, due to attrition within the load and abrasion with the stream bed and banks Why are they rounded? River load in upper course

19. River Transportation Bouncing Rolling Suspension Solution

20. A kettle-like small depressions in the rocky beds of the river valleys are called pot holes which are usually cylindrical in shape. Pot holes are generally formed in coarse-grained rocks e.g. sandstone and granites. The diameter of pot holes ranges from a few centimeters to several meters. They are found in the upper course of a river where it has enough potential energy to erode vertically. The pot holes go on increasing in both diameter and depth. Pot Hole

21. 25 Pot holes , human scale!!

22. Waterfalls Waterfalls occur where there is resistant bedrock, abrupt changes in bedrock resistance, or along fractures or faults in the bedrock. Less resistant materials are weathered more quickly than resistant rocks, creating stair-stepped ledges or drop offs where waterfalls occur. Less resistant rocks may also form pools between resistant rocks that form waterfalls. Faults and fractures often provide natural pathways for the downslope movement of water. The location of the waterfalls origin may be referred to as a “knick-point”, continued weathering by the stream flow causes the knick-point to slowly migrate upstream. Most waterfalls in South Carolina occur along streams in the Blue Ridge, Piedmont, and the along the Regional Fall Line where there are rock layers of varying resistance. This waterfall was formed by differential weathering between the softer shale and harder more resistant limestone. Photo: SCGS Lower White Water Falls in the Jocassee Gorges area of South Carolina drops nearly 200 ft. Here, the Toxaway Gneiss forms a resistant bedrock that the Lower White Water River flows over before draining into Lake Jocasse.

23. Waterfalls

24. Erosion : In this picture, which layers are being eroded to cause undermining? Kaaterskill Falls…

25. Meander = a bend in a river

26. What is a meander?

27. 38 Floodplain Pebble deposits on the inner meander bend where there is low energy River Cliff Slip-Off Slope

28. 39 Meandering Rivers

29. 40 Lower Severn Valley Well developed meanders with bars in the channel indicating high sediment load Very gentle valley side gradients Very wide floodplain

30. Formation of Oxbow lake

31. Ox Bow lake on Mississippi

32. Can you annotate this photo graph ?

33. A flood occurs whenever a river overflows its banks (over ‘bank full discharge’). However, a flood becomes a problem when the water rises to a level where it Destructs property and life. bank full discharge Meander cross section What is a Flood?

34. Flood plains Flood plains are constructive, depositional landforms created by stream flow and sediment deposition. 48 This aerial view of the Mississippi River Valley contains many typical floodplain features. The darker, green areas are floodplain forest and they likely flood the most frequently and thus are not developed with agriculture or housing. The surrounding patchwork represents agricultural fields and other developed lands that are probably at a higher elevation formed by natural or artificial levees. Pointbar Cutbank Oxbow Lakes Infilled Channel

35. The narrow flat surface on either side of the valley floor are called river terrace. Some times, the river valleys are frequented by several terraces on either side wherein they are arranged in step-like forms. River terraces are generally formed due to dissection of fluvial sediments of flood plains deposited along a valley floor. Terrace represents the level of former valley floors and the remnants of former flood plain. River Terrace

36. Floods and Flood Control Floods  A flood occurs when the discharge of a stream becomes so great that it exceeds the capacity of its channel and overflows its banks.  Measures to control flooding include artificial levees, flood control dams, and placing limits on floodplain development.

37. Natural Levees River

38. Stages in the Development of a River Valley

39. The River’s Journey Rivers usually begin in the mountains. They flow downhill onto flat land and into the sea

40. Characteristics of Streams Water always flows downhill, even on the slightest of slopes. The speed of water flow depends upon the slope. As slope increases, the velocity of the water increases.

41. Running Water is the Predominant Agent of Erosion on the Earth Every stream and its branches make up a single system that collects all the runoff within a definite area called the drainage basin of the system. A stream consists of running water, the land surface it drains, the sediment it transports, and the potential energy used to drive it.

42. What determines a streams characteristics Stream Discharge: the volume of water that passes a point in the stream during a given amount of time. The average velocity of a stream increases as its discharge increases.

43. Life History of a Stream YOUTHFUL STREAM Steep gradients V-shaped cross sections Rough sediments flowing rapidly down stream. Due to greater water velocity larger sediment can be moved.

44. Sediments cut through bedrock as they are moved along Common to find rapids and waterfalls due to differences in resistance of the bedrock to weathering.

45. V- Shape Valley

46. Mature Streams Potential energy for cutting and removing rock becomes less. The average gradient is decreased. Velocity near the bed becomes less. The size of sediment that can be moved decreases. Bed becomes covered with loose material, thus protecting it from further erosion.

47. Cutting action of the stream becomes very slow. The base of the V has been widened due to weathering and the action of tributaries the valley now has gentle slopes. Meanders begin to form There is an increase in the volume of water that is carried. A greater mass of sediment can be carried, but most of it is silt and clay.

48. Old Streams Gradient becomes extremely small and only the finest of sediments can be moved. During times of peak flow the banks will overflow and flood the nearby portions of its valley. When the flow subsides a layer of silt and clay is left behind on the valley surface, this is the flood plain.

49. Meanders are strongly looped and from time to time they become cut off to form oxbow lakes.

50. Locations of Stages It is unlikely that any stream is at the same stage of development throughout it entire length. Most streams tend to have the characteristics of youth near their source and of old age near their mouths and to be in the mature stage somewhere in-between. A stream can be rejuvenated through crustal uplift.

51. The river cuts downward to form a ‘V’shaped valley. The river starts to meander

52. River uses its meanders to cut from side to side eating into the valley Floodplain starts to form 1 2

53. 1 2

54. Formatioin of Valleys

55. A lluvium = silt deposited by a river Alluvial fan Caused when a stream falling from a side valley reaches flatter ground on the valley floor. Material is dropped at the ‘ break of slope’ to form this fan shape. (This is really a depositional feature.) Erosion/Deposition

56. Alluvial fan

57. Deltas Deltas form where the mouth of a river meets its ultimate base level at the ocean or sea. As the river’s velocity decreases, it looses the capacity to carry its sediment load and the resulting deposits form a delta. Delta shapes and forms vary depending on tidal influences, waves, currents, sediment type and quantity, river discharge, and the stream gradient near the outlet. The most common types of deltas include bird-foot, estuarine, and arcuate . Not all rivers form deltas, for example the Amazon deposits its sediment load directly into the ocean onto an underwater seaward sloping continental shelf. The Columbia River in the northwest United States, lacks a delta altogether, because the currents are too strong and erosive for the sediments to deposit. Mississippi River Delta: Bird-Foot Delta A bird-foot delta contains a large channel with multiple smaller distributary channels draining off from the main channel and depositing sediments. They generally form with rivers that have a high sediment load and flow into an area with minimal tidal influences. This false-color infrared image provides a satellite view of the Mississippi River delta. This delta has shifted positions several times over the last 5000 years in relation to changes in the Mississippi River. Scientist recognize atleast 7 distinct deltas. The most recent began forming 500 years ago and forms a classic bird-foot delta.

58. Deltas Nile River and Arcuate Delta ACE Basin: Estuarine Delta

59. 78 River Nile The Nile Delta, satellite view

60. Formation of Delta

61. That’s all about River & Its Associated Landforms