Classroom presentations to accompany Understanding Earth , 3rd edition

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