Transcript RIVERS AND STREAMS

CHAPTER 16
SURFACE
WATER
RIVERS & STREAMS
•
•
•
•
•
•
The Hydrologic Cycle
Water Reservoirs
Surface Water Systems
Surface Water Flow
Sediment Transport
Stream System
Components
• Floods and Flooding
• Pollution
What is the Cycle of Water on
Earth’s Surface?
• The hydrologic cycle is a summary of the
circulation of Earth’s water supply.
• Processes involved in the hydrologic cycle:
• Precipitation
• Evaporation
• Infiltration
• Runoff
• Transpiration
The Hydrologic Cycle
Figure 16.3
• Infiltration = Groundwater System
• Runoff = Surface Water System
• Runoff = Precipitation – Evapotranspiration
Where is the Water ?
Figure 16.2
L a rg e s t R iv e rs o f th e W o rld
A p p r o x . le n g th
R iv e r
O u tflo w
N ile M e d ite r r a n e a n S e a
m i.
4 ,1 8 0
km
6 ,6 9 0
A m a z o n A tla n tic O c e a n
3 ,9 1 2
6 ,2 9 6
M is s is s ip p i-M is s o u r i G u lf o f M e x ic o
3 ,7 1 0
5 ,9 7 0
Y a n g tz e K ia n g C h in a S e a
3 ,6 0 2
5 ,7 9 7
O b G u lf o f O b
3 ,4 5 9
5 ,5 6 7
H u a n g H o (Y e llo w ) G u lf o f C h ih li
2 ,9 0 0
4 ,6 6 7
Y e n is e i A r c tic O c e a n
2 ,8 0 0
4 ,5 0 6
P a r a n á R ío d e la P la ta
2 ,7 9 5
4 ,4 9 8
2 ,7 5 8
4 ,4 3 8
2 ,7 1 6
4 ,3 7 1
2 ,7 0 4
4 ,3 5 2
2 ,6 5 2
4 ,2 6 8
2 ,6 3 5
4 ,2 4 1
N ig e r G u lf o f G u in e a
2 ,6 0 0
4 ,1 8 4
M e k o n g S o u th C h in a S e a
2 ,5 0 0
4 ,0 2 3
2 ,3 4 8
3 ,7 7 9
2 ,3 1 5
3 ,7 2 6
2 ,2 9 1
3 ,6 8 7
M a d e ir a A m a z o n R iv e r
2 ,0 1 2
3 ,2 3 8
P u r u s A m a z o n R iv e r
1 ,9 9 3
3 ,2 0 7
1 ,9 8 7
3 ,1 9 8
1 ,9 7 9
3 ,1 8 5
1 ,9 0 0
3 ,0 5 8
1 ,8 8 5
3 ,0 3 4
1 ,8 0 0
2 ,8 9 7
1 ,8 0 0
2 ,8 9 7
D a n u b e B la c k S e a
1 ,7 6 6
2 ,8 4 2
E u p h r a te s S h a tt-a l-A r a b
1 ,7 3 9
2 ,7 9 9
D a r lin g M u r r a y R iv e r
1 ,7 0 2
2 ,7 3 9
1 ,7 0 0
2 ,7 3 6
1 ,6 7 7
2 ,6 9 9
Ir tis h O b R iv e r
Z a ir e (C o n g o ) A tla n tic O c e a n
H e ilo n g (A m u r ) T a ta r S tr a it
L e n a A r c tic O c e a n
M a c k e n z ie B e a u fo r t S e a (A r c tic O c e a n )
M is s is s ip p i G u lf o f M e x ic o
M is s o u r i M is s is s ip p i R iv e r
V o lg a C a s p ia n S e a
S ã o F r a n c is c o A tla n tic O c e a n
Y u k o n B e r in g S e a
S t. L a w r e n c e G u lf o f S t. L a w r e n c e
R io G r a n d e G u lf o f M e x ic o
B r a h m a p u tr a G a n g e s R iv e r
In d u s A r a b ia n S e a
Z a m b e z i M o z a m b iq u e C h a n n e l
T o c a n tin s P a r á R iv e r
The
World’s
Largest
Rivers
by
Length
The World’s Largest Rivers by Discharge
Discharge
River
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Amazon, Brazil
Congo, Zaire
Yangtse Kiang, China
Orinoco, Venezuela
Brahmaputra, Bangladesh
La Plata, Brazil
Yenissei, Russia
Mississippi, USA
Lena, Russia
Mekong, Vietnam
Ganges, India
Irrawaddy, Burma
Ob, Russia
Sikiang, China
Amur, Russia
St. Lawrence, Canada
m^3/sec
190,000
42,000
35,000
29,000
20,000
19,500
17,800
17,700
16,300
15,900
15,500
14,000
12,500
11,500
11,000
10,400
% of total
Runoff
mm/yr entering
Ratio
oceans
835
340
560
845
1070
235
215
175
210
630
455
1020
135
840
190
310
13.0
2.9
2.4
2.0
1.4
1.3
1.2
1.2
1.1
1.1
1.1
1.0
0.9
0.8
0.8
0.7
0.47
0.25
0.50
0.46
0.65
0.20
0.42
0.21
0.46
0.43
0.42
0.60
0.24
0.32
0.33
U.S. Precipitation Map
Notice the effect of
the Rocky Mountains
U.S. Runoff Map
What is the
Function of
Streams?
(From the Geologic
Perspective, of
course)
The main
function of a
stream is to
remove excess
surface water
from the
continent.
How Do Streams Remove
Water from the Continent?
• By Stream Flow – Two types
determined primarily by velocity:
• Laminar
Flow
• Turbulent
Flow
Near-Laminar flow in the
center of a river channel
Turbulent flow in the
headwaters of a rushing
mountain stream
Factors that Determine Velocity
• Gradient, or slope.
• Channel
Characteristics
including:
– shape
– size
– roughness.
• Discharge
So Where Does Streams Flow
the Fastest (Highest Velocity)?
• Headwaters move
slowest.
• Mouth of stream moves
fastest.
• Laminar flow is more
efficient than turbulent
flow.
• Deeper streams move
faster than shallower
streams.
How much
water do
streams
remove from
a continent?
Discharge – the volume of water
moving past a given point in a certain
amount of time.
Discharge (m3/s) = channel
width(m) X channel depth(m) X
velocity(m/s)
• Highly variable in most streams.
• When discharge increases, velocity and
channel cross-sectional area both increase.
Stream bank
0.6D
D

Q   V  dA
- Velocity measurements V
Pygmy Meter
A
Price Meter
RATINGS CURVE
Collect stage data continuously, transform it to discharge data
To get a bit of experience with stream gaging and analysis of stream data, visit
http://vcourseware4.calstatela.edu/VirtualRiver/FloodingDemo/index.html and
play with it!!!
World’s Largest Rivers Ranked
by Discharge
How Do
Streams:
Affect the Land
Surface
(and Geology)?
While rivers
are removing
water from
the continent:
• They carve the landscape forming erosional
geologic features.
• The erode existing geologic formations (rocks).
• Transport the sediments.
• Deposit new geologic formations.
Streams
Carve the
Landscape by
Erosion
• Lift loosely consolidated particles by:
• Abrasion (Mechanical Weathering)
• Dissolution (Chemical Weathering)
• Stronger currents lift particles more effectively.
• Create stream valleys and other erosional features.
How Do Streams Transport Eroded
Sediments to Deposit New Geologic
Formations?
• Streams transport sediment via stream
loads.
• Types of Stream
Load:
– Dissolved Load
– Suspended
Load
– Bed Load
Movement of Bed
Load by Saltation
Animation #75: Sediment
Transport by Streams
– Capacity – the maximum load a stream can transport.
– Competence
• Indicates the maximum particle size a stream can transport.
• Determined by the stream’s velocity.
How Do
Streams:
Affect the Land
Surface
(and Geology)?
Ultimately,
Erosion by
Surface Water
Returns the
Surface of the
Continent to
Equilibrium.
(equilibrium being base
level = sea level)
In other words, what
goes up (mountains)
must come down.
Life Cycle of a Stream
• Streams erode the highlands and deposits
those sediments in the lowlands/
continental edge.
• Begins with the Hydrologic Cycle.
• As the stream evolves
from young to mature,
it shifts from being
predominantly
erosional to
depositional.
Changes from Upstream to Downstream
• Longitudinal Stream Profile:
– Cross-sectional view of a stream.
– Viewed from the head (headwaters or
source) to the mouth of a stream.
– Profile is a
smooth curve.
– Gradient
decreases
downstream.
Longitudinal Stream Profile
Can be divided into 3 main parts
Drainage System
Transport System
Distributary
System
Functions of Three Stream Phases
• Drainage (Tributary) Systems:
– Collect water (and sediments)
• Transport Systems:
– Move water along (and sediments)
• Distributary Systems:
– Return water (and sediments) to
the sea
Changes from Upstream to Downstream
• Factors that increase
downstream
– Velocity
– Discharge
– Channel Size
• Factors that decrease
downstream
– Gradient
– Channel Roughness
Drainage System: Youthful Streams
• Stream energy is spent eroding downward into the
basement rock (downcutting toward base level) and...
• Moving Sediment – Very Course- to Very Fine-Grained
• Creates “V” Shaped Canyons and Valleys
• Stream Occupies Entire Valley Floor
• Smaller Channel Size
• Greater Channel Roughness
• Straighter Stream Path
• Higher Gradient
• Lower Velocity
• Lower Discharge
• Fewer Tributaries
• Features often include rapids, waterfalls, and alluvial fans
• Rock Types: Conglomerates, Breccias, Arkosic
Sandstones, Graywacke Sandstones, etc.
The Drainage Systems of Youthful
Streams End at the Base of the
Mountains Where Alluvial Fans are
Deposited.
Alluvial Fans
Transition from Drainage to Transport Systems
• Alluvial Fans
– When high-gradient streams emerge from the narrow
valley of a mountain front, they often deposit some of
this sediment forming alluvial fans.
• Due to a dramatic
decrease in velocity.
• Causing Sediment to
drop out of suspension.
• Slopes outward in a
broad arc similar to a
delta.
Coalescing Alluvial Fans
Transport System:
Braided Streams
• High sediment load.
• Anastamosing channels.
• Constantly changing
course.
• Floodplain completely
occupied by channels.
• Many small islands
called mid-channel bars.
• Usually coarse sand and
gravel deposits.
Transport System
Mature Streams: Meandering Rivers
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•
•
•
•
•
•
Stream is near base level
Stream energy is spent eroding and depositing laterally
Downward erosion is less dominant
Constantly erode material - Cut bank
Constantly deposit material - Point bar
Channel changes course gradually as stream migrates from side-to-side
(meanders)
Create floodplains (broad or U-shaped stream valley) wider than the channel
(occupies small portion of valley floor)
– Very Fertile soil
– Subjected to seasonal flooding
•
•
•
•
•
•
•
•
Larger Channel Size
Smooth Channel Bottom
Wandering and Curved Stream Path
Low Gradient
Higher Velocity
Higher Discharge
Greater Number of Tributaries
Rock Types: Quartz Sandstones, Siltstones, Mudstones, Shales, Coal, etc.
Transport System
Mature Streams: Meandering Rivers
• Features of mature streams often include:
• Floodplains
Animation #81: Stream
Processes – Floodplain
Development
Transport System
Mature Streams: Meandering Rivers
• Features of mature streams often include:
• Meanders
– Cut Banks and
Point Bars
– Cutoffs and
Oxbow Lakes
Erosion and Deposition Along
a Meandering Stream
Figure 16.14
Formation of Meanders
Point
bar
deposits
Point Bar Deposits
Point bar deposits grows laterally
through time
Cut bank erosion
Point
bar
deposits
}
Meander
loop
Erosion of a Cutbank
Formation of an Oxbow
Meanders and
Oxbow Lake
Green River,
Wyoming
Mississippi Meanders
Meandering stream
flowing from
top of screen
to bottom
Maximum
deposition
Maximum
erosion
Meander scars
Oxbow Lake
Oxbow
cuttoff
Animation #83: Stream
Processes – Floodplain
Development and Oxbow
Lakes
Transport System
Mature Streams: Meandering Rivers
• Features of mature streams often include:
• Floodplain Deposits
– Natural Levees –
form parallel to the
stream channel by
successive floods
over many years
– Back Swamps
– Yazoo Tributaries
Distributary System: Deltas
• Deltas – Form when a stream enters an
ocean or lake.
• Characteristic of mature streams.
• Consists of three
types of beds:
– Foreset Beds
– Topset Beds
– Bottomset Beds
Delta Shapes
Fan Delta
Bird-Foot Delta
Things to Remember
• Streams area part of a larger hydrologic system.
• The main function of a stream is to remove excess surface water from
the continent.
• Ultimately, erosion by surface water returns the surface of the
continent to equilibrium (equilibrium being base level).
• While rivers are removing water from the continent:
–
–
–
–
They carve the landscape forming erosional geologic features.
The erode existing geologic formations.
Transport the sediments.
Deposit new geologic formations.
• Streams have three main components:
– Drainage (Tributary) Systems – collect water
– Transport Systems – move water along
• Alluvial fans, braided streams, meandering streams
– Distributary Systems – return water to the sea
• Deltas
• As the stream evolves from young to mature, it shifts from being
predominantly erosional to depositional.
• Summary of Stream Chacterisitics.
Summary Stream Characteristics
Summary of Stream Life Cycle Characteristics
Characteristic
YOUNG
OLD
Valley Shape
V-Shaped
Broad or U-Shaped
(Steep-Sided Channel Walls)
(Gently-Sloped Channel Walls)
Channel Size
Smaller
Larger
River Occupying Valley Floor
Occupies Entire Valley Floor
Occupies Small Portion of Valley Floor
Channel Roughness
Rough
Smooth
Stream Gradient
High
Low
Stream Velocity
Lower
Higher
Stream Discharge
Lower
Higher
Number of Tributaries
Smaller
Greater
Erosional Style
Downcutting and Headward Erosion
Migration (Side-to-Side) and Meandering
Proximity to Base Level
Stream is above base level
Stream is near base level
Ability to Transport Sediment
Very Course- to Very Fine-Grained
Pebble--Sand--Silt--Clay (Finer-Grained)
Rock Types
Conglomerates
Quartz Sandstones
Breccias
Siltstones
Arkosic Sandstones
Mudstones
Graywacke Sandstones
Shales
Coal
Energy (Due to Gradient)
High (Dams for Power Supply)
Low (Dams for Water Supply)
Summary Stream Characteristics
Summary of Stream Life Cycle Characteristics
Characteristic
YOUNG
OLD
Erosional Features
Wind Gaps
Cut Banks
Water Gaps
Rapids
Waterfalls
Depsitional Features
Alluvial Fans
Deltas
Flood Plains
Natural Levees
Incised Meanders (Rejuvinated)
Meanders
Point Bars
Meander Scars
Cutoffs
Oxbow Lakes
Terraces (Rejuvinated)
Terraces
Back Swamps
Yazoo Tributaries
Note: Braided Streams are Intermediate Features Transitional Between Young and Old Streams
How Does
Geology Affect
Stream
Development
and Flow?
Drainage Networks
• Land area that contributes water to
the stream is the drainage basin.
• Imaginary line
separating one
basin from
another is
called a divide.
Drainage Basin of the
Mississippi River
Figure 16.31
Drainage Patterns
• Pattern of the interconnected
network of streams in an area
– Common drainage patterns
• Dendritic
• Radial
• Rectangular
• Trellis
Drainage Patterns
Figure 16.32
Base Level and Graded Streams
• Base level is the lowest point to which a
stream can erode.
– Two general types of base level:
– Ultimate (sea level)
– Local or temporary
– Changing conditions causes readjustment
of stream activities:
– Raising base level causes deposition
– Lowering base level causes erosion
» Uplift of the region
Adjustment of Base Level
to Changing Conditions
Figure 16.9
Rejuvenated Streams
• Incised Meanders
– Meanders in steep, narrow valleys.
– Caused by a drop in base level or uplift of the
region.
Incised Meanders of the Delores
River in Western Colorado
A Meander Loop on the
Colorado River
Rejuvenated Streams
• Terraces
– Remnants of a former floodplain.
– River has adjusted to a relative drop in base
level by downcutting.
Floods and Flood Control
Floods and Flood Control
• Floods are the most common and
most destructive geologic hazard
– Causes of Flooding:
• Naturally occurring factors
• Human-induced factors
Floods and Flood Control
• Types of Floods
– Regional Floods
– Flash Floods
– Ice-Jam Floods
– Dam Failure
– Levee Breach
Regional Flood Recurrence,
Skykomish R.
Want some stream flow data? Try: http://water.usgs.gov/
Flash Flooding & Sheetwash
Flash Flooding & Sheetwash
Floods and Flood Control
• Flood Control
• Engineering Efforts
– Artificial Levees
– Flood-Control Dams
– Channelization
• Nonstructural approach through sound
floodplain management
Flooding, Sedimentation, and
Natural Levee Formation
Formation of Natural Levees
Figure 16.16
Natural
Levees
Artificial Levee Diagram
Levee Breach
Floods and Flood Control
• Causes of 1993 Mississippi Flooding
• There were four principal reasons why flooding was so
extensive:
– The region received higher than normal precipitation
during the first half of 1993. Much of the area received
over 150% of normal rainfall and parts of North Dakota,
Kansas, and Iowa received more than double their typical
rainfall.
– Individual storms frequently dumped large volumes of
precipitation that could not be accommodated by local
streams.
– The ground was saturated because of cooler than normal
conditions during the previous year (less evaporation) so
less rainfall was absorbed by soils/air and more ran-off
into streams.
– The river system had been altered over the previous
century by the draining of riverine wetlands (80% since
the 1940s) and the construction of levees (many of which
failed under the weight of the floodwaters).
– Source:http://lists.uakron.edu/geology/natscigeo/lectures/streams/miss_fl
ood.htm#sum
Satellite Views of the
Missouri/Mississippi Flood in 1993.
1993 Mississippi Flood
Mississippi Deltas over the Last
5000-6000 Years
http://www.nola.com/speced/lastchance/multimedia/credits.swf
If the
Mississippi
changes course
again, what
will happen to
the City of
New Orleans?
New Orleans Levee System
New Orleans Levee System
New Orleans Levee System
http://www.nola.com/katrina/graphics/flashflood.swf
Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
• Anacostia River is eight miles
long.
• Severely polluted by sediment,
nutrients, pathogens, toxins and
trash.
• Because the Anacostia is
relatively flat and extremely tidal,
it especially vulnerable to
contamination.
• It's unsafe to swim in the
Anacostia, or to eat its fish.
An aerial view of the Anacostia River
(far right) at its confluence with the
Potomac River. The dramatic difference
in color is due to the high level of
sediments from CSOs and stormwater
runoff.
http://www.nrdc.org/water/pollution/fanacost.asp
Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
• The river's decline began as
settlers cleared fields for
agriculture (leading to heavy
erosion and sedimentation).
• Urbanization claimed forest
and wetland habitat, altered
stream flows, and fed everincreasing flows of sewage
and polluted runoff into the
Anacostia.
http://www.nrdc.org/water/pollution/fanacost.asp
A river designated for swimming,
fishing, and other recreation is
instead an eyesore, as this floating
debris testifies.
Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
• Between 75 percent and 90 percent of the Anacostia's
pollution is caused by stormwater runoff.
• A problem closely tied to sprawl and overdevelopment
throughout the watershed.
• More development means more hard surfaces -- more
roads, sidewalks, parking lots and rooftops.
• As a result, water that was once absorbed and filtered by
soil and plants now rushes across pavement, picking up
nitrogen, phosphorous, oil, heavy metals, bacteria and
viruses, which are dumped directly into the river.
http://www.nrdc.org/water/pollution/fanacost.asp
Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
• Stormwater also plays a role in combined
sewer overflows (CSOs), which are the
other major source of pollution to the
Anacostia.
• Like many older cities, Washington uses a
sewer system that carries both sewage and
stormwater in the same set of pipes.
• When it rains, the system rapidly becomes
overwhelmed and begins discharging
untreated sewage into local waterways.
• Along the Anacostia's short course, such
overflows occur in 17 different places,
spilling 2 to 3 billion gallons into the river
each year.
http://www.nrdc.org/water/pollution/fanacost.asp
The District of Columbia's centuryold sewage and flood control system
is designed to overflow when it
rains. As a result, untreated sewage
and stormwater spills into the river
at 17 different discharge points.