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Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 13 Streams:

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Presentation on theme: "Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 13 Streams:"— Presentation transcript:

1 Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 13 Streams: Transport to the Ocean

2 Gary D. McMichael/Photo Researecher

3 Rivers and streams Stream : body of water flowing in a channel The floor of the channel is called the bed. When rainfall is very heavy or snow melts rapidly, bodies of water overflow their banks and water covers the adjacent land called the floodplain.

4 Rivers and streams Carry away runoff to lakes and seas Erode land (degradation) Transport and deposit sedimentary debris

5 Stream behavior Mostly determined by velocity and shape of channel. These factors combine to allow either laminar or turbulent flow. Turbulent flow is much more erosive. Stream velocities may vary from 0.25 to 7 m/s.

6 Laminar flow Smooth sheet-like flow at a low velocity Usually confined to edges and top of stream

7 Turbulent flow Irregular swirling flow Occurs at most rates of stream flow Keeps particles in suspension

8 Laminar flow Fig. 13.1a

9 Turbulent flow Fig. 13.1b

10 Laminar to turbulent transition Fig. 13.1c ONERA Laminar flowTurbulent flow

11 Streams move material in three forms Dissolved load Suspended load Bed load (traction and saltation)

12 Fig Sediment Transport

13 Fig Saltation

14 Fig Grain Size and Flow Velocity

15 Stream terms competence: measure of the largest particles a stream can transport proportional to v 2 capacity: maximum quantity of sediment carried by stream proportional to Q and v

16 Lower Velocities Form Ripples Fig. 13.5a ripple

17 Higher Velocities Form Dunes Fig. 13.5b ripples dune

18 Pebbles Caught in Eddies Form Potholes Fig Carr Clifton/Minden Pictures

19 Waterfall Retreating Upriver Fig Donald Nausbaum

20 Fig Parts of a River System

21 Two important stream types 1. Meandering Streams Gentle gradients, fine-grained alluvium Minimizes resistance to flow and dissipates energy as uniformly as possible (equilibrium) Examples: point bars,oxbow lake, migrating meanders

22 Two important stream types 2. Braided Streams Sediment supply greater than amount stream can support. At any one moment the active channels may account for only a small proportion of the area of the channel system, but essentially all is used over one season. Common in glacial, deserts, and mountain regions.

23 Fig Incised Meanders, Utah Tom Bean

24 Fig Meandering River Over Time

25 Fig a Lateral migration by erosion at the outside & deposition on the inside of the river

26 Fig Meandering River Point Bar Peter Kresan

27 Fig Braided River Tom Bean

28 Fig Formation of Natural Levees

29 Discharge Total amount of water that passes a given point in a stream per unit time Q = w d v

30 Discharge Discharge (m 3 /s) = width (m)  depth (m)  average velocity (m/s) In the U.S., this is expressed as cubic feet per second (cfs): 1 m 3 /s = 35.9 ft 3 /s

31 Fig a River at Low Discharge

32 River at High Discharge Fig b

33 Flooding Water in the stream is greater than the volume of the channel. Interval between floods depends on the climate of the region and the size of the channel/

34 City Built on a Floodplain Xie Jiahua/China Features/Sygma

35 Recurrence interval Average time between the occurrences of a given event The recurrence interval of a flood of a given size at a given place depends on: climate of the region width of the floodplain size of the channel

36 Fig Annual Flood Frequency Curve

37 Fig Longitudinal Stream Profile of the Platt and South Platt Rivers

38 Base level Elevation at which a stream enters a large body of water such as a lake or ocean

39 Role of Base Level in Controlling Longitudinal Profile of Rivers Fig

40 Effects of Building a Dam Original Profile Graded to Regional Base Level Fig a

41 Effects of Building a Dam Dam Forms New Local Base Level Fig b

42 Effects of Building a Dam Deposition Upstream and Erosion Downstream Fig c

43 Graded stream Stream in which neither erosion nor deposition is occurring, due to an equilibrium of slope, velocity, and discharge.

44 Geologic evidence of changes in stream equilibrium Alluvial fans Terraces: erosional remnants of former floodplains

45 Fig Alluvial Fans Michael Collier

46 Formation of River Terraces Fig

47 Fig Drainage divides separate adjacent drainage basins

48 Drainage basin Area of land surrounded by topographic divides in which all the water is directed to a single point

49 Fig Drainage Basin of the Colorado River

50 Fig Typical Drainage Networks

51 Antecedant Stream Fig &b Stream was present before deformation Deformation causes gorge to form

52 Fig A Superimposed Stream Deformation occurred before stream was present Downcutting causes gorge to form

53 Fig c Delaware Water Gap A Superimposed Stream Michael P. Godomski/Photo Researchers

54 Delta Location of significant sedimentation where a river meet the sea.

55 Fig Mississippi Delta Landsat 2 image annotated by Moore, 1979

56 Fig Typical Large Marine Delta

57 Fig Shifting Mississippi River Delta Over the Past 6000 Years


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