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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: Transport to the Ocean. Streams: Transport to the Ocean. Gary D. McMichael/Photo Researecher. - PowerPoint PPT Presentation
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Classroom presentations to accompany
Understanding Earth, 3rd edition
prepared by
Peter Copeland and William Dupré
University of Houston
Chapter 13Chapter 13Streams: Transport to the Ocean
Streams: Streams: Transport to the Transport to the
OceanOcean
Gary D. McMichael/Photo Researecher
Rivers and streamsRivers 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.
Rivers and streamsRivers and streams
• Carry away runoff to lakes and seas
• Erode land (degradation)
• Transport and deposit sedimentary debris
Stream behavior 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.
Laminar flowLaminar flow
• Smooth sheet-like flow at a low velocity
• Usually confined to edges and top of stream
Turbulent flowTurbulent flow
• Irregular swirling flow
• Occurs at most rates of stream flow
• Keeps particles in suspension
Laminar flow
Fig. 13.1a
Turbulent flow
Fig. 13.1b
Laminar to turbulent transition
Fig. 13.1cONERA
Laminar flow Turbulent flow
Streams move material Streams move material in three formsin three forms
• Dissolved load
• Suspended load
• Bed load (traction and saltation)
Fig. 13.2
Sediment Transport
Fig. 13.3
Saltation
Fig. 13.1
Grain Size and Flow Velocity
Stream terms Stream terms
competence: measure of the largest particles a stream can transport proportional to v2
capacity: maximum quantity of sediment carried by stream proportional to Q and v
Lower Velocities Form Ripples
Fig. 13.5a
ripple
Higher Velocities Form Dunes
Fig. 13.5b
ripples
dune dune
Pebbles Caught in
Eddies Form
Potholes
Fig. 13.6Carr Clifton/Minden Pictures
Waterfall Retreating Upriver
Fig. 13.7Donald Nausbaum
Fig. 13.8
Parts of a River SystemParts of a River System
Two important stream typesTwo important stream types
1. Meandering Streams1. 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
Two important stream typesTwo important stream types
2. Braided Streams2. 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.
Fig. 13.9
Incised Meanders, Utah
Tom Bean
Fig. 13.10
Meandering River Over Time
Fig. 13.10a
Lateral migration by erosion at the outside
& deposition
on the insideof the river
Fig. 13.11
Meandering River
Point Bar
Peter Kresan
Fig. 13.12
Braided River
Tom Bean
Fig. 13.1
Formation of Natural Levees
DischargeDischarge
Total amount of water that passes a
given point in a stream per unit time
Q = w d v
DischargeDischarge
Discharge (m3/s) = width (m) depth (m) average velocity (m/s)
In the U.S., this is expressed as cubic feet per second (cfs):
1 m3/s = 35.9 ft3/s
Fig. 13.14a
River at Low Discharge
River at High Discharge
Fig. 13.14b
FloodingFlooding
• 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/
City Built on a Floodplain
Xie Jiahua/China Features/Sygma
Recurrence intervalRecurrence interval
Average time between theoccurrences of a given event
The recurrence interval of a flood ofa given size at a given place depends on:
• climate of the region• width of the floodplain• size of the channel
Fig. 13.1
Annual Flood Frequency Curve
Fig. 13.16
Longitudinal Stream Profile of the Platt and South Platt Rivers
Base levelBase level
Elevation at which a streamenters a large body of water such
as a lake or ocean
Role of Base Level in Controlling Longitudinal Profile of Rivers
Fig. 13.17
Effects of Building a DamOriginal Profile Graded to Regional
Base Level
Fig. 13.18a
Effects of Building a DamDam Forms New Local Base Level
Fig. 13.18b
Effects of Building a DamDeposition Upstream
and Erosion Downstream
Fig. 13.18c
Graded streamGraded stream
Stream in which neither erosion nor
deposition is occurring, due to an
equilibrium of slope, velocity, and
discharge.
Geologic evidence of changesGeologic evidence of changesin stream equilibriumin stream equilibrium
• Alluvial fans
• Terraces: erosional remnants of former floodplains
Fig. 13.19
Alluvial Fans
Michael Collier
Formation of River Terraces
Fig. 13.20
Fig. 13.21
Drainage divides separate adjacent drainage basins
Drainage basinDrainage basin
Area of land surrounded by
topographic divides in which all the
water is directed to a single point
Fig. 13.22
Drainage Basin of the Colorado River
Fig. 13.23
Typical Drainage Networks
Antecedant Stream
Fig. 13.24&b
Stream was present before deformation
Deformation causes gorge to form
Fig. 13.25
A Superimposed StreamDeformation occurred before stream was present
Downcutting causes gorge to form
Fig. 13.24c
Delaware Water Gap A Superimposed Stream
Michael P. Godomski/Photo Researchers
DeltaDelta
Location of significant
sedimentation where a river meet
the sea.
Fig. 13.26
Mississippi Delta
Landsat 2 image annotated by Moore, 1979
Fig. 13.27
Typical Large Marine Delta
Fig. 13.28
Shifting Mississippi River Delta Over the Past 6000 Years