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Chapter Fourteen Streams & Floods. Earth’s Water Water in, on, and above Earth is ~ 1.36 billion km 3 (326 million mile 3 ) and this amount is fairly.

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Presentation on theme: "Chapter Fourteen Streams & Floods. Earth’s Water Water in, on, and above Earth is ~ 1.36 billion km 3 (326 million mile 3 ) and this amount is fairly."— Presentation transcript:

1 Chapter Fourteen Streams & Floods

2 Earth’s Water Water in, on, and above Earth is ~ 1.36 billion km 3 (326 million mile 3 ) and this amount is fairly constant The continuous circulation of water through the ocean, land and the atmosphere is the process called hydrologic cycle Distribution of Earth’s water  97.2 % in ocean; 2.15% ice/glacier; 0.65% Lakes, Streams, Groundwater, Atmosphere Types of water  Juvenile- initial Earth’s water  Meteoric- nearly all surface water originates in the atmosphere

3 Distribution of the Earth’s water: by volume

4 Hydrologic Cycle

5 A stream system network

6 Anatomy of a Stream A stream is a surface water flow confined to a channel Floodplain - flat land immediately surrounding a stream which may be submerged if a river overflows its bank Drainage Basin- areas of land that supply their water Drainage Divide - topographic highland that separates two adjacent drainage basins Tributaries - streams that contribute water to main (trunk) stream Distributaries - main river splits into small channels that empties into a lake/sea Graded Stream - state of temporary equilibrium Base level - lowest point to which a river can erode Discharge - the amount of water that flows through a given area (Q=V*A)

7 Streamflow & Discharge Gradient = Change in elevation per distance – Ranges from 66 m/km (in mountains) to 0.1 m/km (on lowland plains) – Turbulent Flos: Non streamline flow – Stream Velociy: Velocity = Distance traveled in a given time Ranges from >10 m/s to 0.27 m/s Local velocity depends on: continental gradient, location of water within channel (slowest in straight segment at sides & bottom; velocity greatest at the outside of the curve; fastest in straight segment in top center, in curved segment: top on inside of curve, narrow places than in wide ones) Velocity greater downstream than upstream because greater volume of water and stream bed is smoother Stream discharge: Volume of water passing a given point for a given time Discharge = (Width X Depth X Velocity) / 2 (for a hypothetical square or rectilinear stream, factor 2 is not there)

8 Streamflow and Discharge – contd. Discharge depends on: – Size of drainage basin – Amount of precipitation in basin – Ranges from 200,000 to 5 m3/s (one day in Amazon for more than 5 yrs of New York need) – GEOLOGICAL WORK OF STREAMS Stream Erosion Graded Streams- No net erosion, no net deposition (dynamic equilibrium)  Aggregation- too much sediments-increased sediment load – steeper gradient – increases stream’s velocity - Regrading  Degradation- occurs when there is less sediments – steeper gradient - Regrading  Abrasion: Scouring of Particles  Hydraulic lifting – Erosion by water pressure  Dissolution: Dissolution of soluble bedrock

9 Stream Transport Streams erode their networks of tributary valleys and distinctive drainage patterns. A drainage pattern is a reflection of the underlying rock material or structure. Drainage Types (Patterns)  Dendritic: Branching drainage pattern – develop on relatively flat sedimentary rocks  Radial: Streams typically drain from a Central high area like spoks of a wheel  Rectangular: Looks like a grid of city streets  Trellis: Develops where narrow valleys are separated by parallel ridges Stream Piracy Superposed/Antecedent streams Channel patterns- straight, braided or meandering, oxbow lake

10 Aggradation & Degradation of graded streams

11 Four types of drainage pattern

12 Four types of drainage patterns – contd.

13 Four types of drainage pattern – contd.

14 Four types of drainage patterns – contd.

15 Channel Patterns Straight Channels: In areas of active uplife Braided streams: Networks of converging and diverging stream channels separated by sand & gravel bars Meandering Streams: Oxbow Lakes

16 Sediment Deposition Velocity of sediment transport is controlled by its discharge Stream Capacity- the total volume of sediments it carries is controlled by its discharge Competence- the maximum size of sediments a stream carries is controlled by its velocity Sediments are transported in the following format  Suspended load  Bed load  Dissolved load

17 Superposed streams

18 Superposed streams – contd.

19 Antecedent streams

20 Antecedent streams – contd.


22 Evolution of meandering streams

23 Pronounced stream meander bends

24 Waterfalls & Rapid Waterfall Formation Waterfall migration upstream Waterfall reduction to rapids Niagara Falls Stream Transport: – Capacity = Maximum possible sediment load that a stream can transport; proportional to stream discharge – Competence = largest possible sediment that a stream can transport; proportional to the square of a stream’s velocity.

25 Evolution of waterfalls and rapids

26 Evolution of waterfalls & rapids – contd.

27 The creation of stream terraces

28 Creation of stream terraces – contd.


30 Sediment Distribution

31 Floodplain features

32 Anatomy of a delta

33 Stream Deposition Alluvium- sediment materials that settle from water Point bar- sediments deposited within the channel Flood plain Deposits  Levees  Backswamp- deposits that make a flood plain’s wetland Alluvial fans- formed where stream valley widens Delta- formed by the deposition of sediments in standing water where the main stream breaks into smaller channels

34 Large sediment loads

35 The evolution of the Mississippi River delta plain

36 Hydrographs - Illustrations

37 Hydrographs - Charts

38 A flood frequency curve for a hypothetical stream

39 Controlling Floods Floods occur every 2 to 3 years Flooding caused when runoff is greater than stream channel can carry Flood Prediction: – Seasonal flooding – Predicting Extreme Floods Statistical probability Stream hydrographs 10-yr and 100-yr floods Difficulty of Predicting Floods Inadequate Records underestimate 100-yr floods Human development increases maximum discharge Inadequacy of statistical probability

40 Flood Prevention Artificial Strategies: – Artificial Levees & Flood walls – Flood-control dams – Channelization: Benefits and problems – Drawbacks to structural solutions: cost and false sense of security – Nonstructural Strategies: Identifying high-risk areas Zoning against floodplain development Managing resources to minimize floodwaters

41 Artificial levees & flood wells

42 Artificial levees and flood walls – contd.

43 Artificial levees & flood walls – contd.

44 Flood-hazard map

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