2. RIVERS & STREAMS
• The Hydrologic Cycle
• Water Reservoirs
• Surface Water Systems
• Surface Water Flow
• Sediment Transport
• Stream System
Components
• Floods and Flooding
• Pollution
3. 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
4. The Hydrologic Cycle
• Infiltration = Groundwater System
• Runoff = Surface Water System
• Runoff = Precipitation – Evapotranspiration
Figure 16.3
6. The
World’s
Largest
Rivers
by
Length
Largest Rivers of the World
River Outflow mi. km
Nile Mediterranean Sea 4,180 6,690
Amazon Atlantic Ocean 3,912 6,296
Mississippi-Missouri Gulf of Mexico 3,710 5,970
Yangtze Kiang China Sea 3,602 5,797
Ob Gulf of Ob 3,459 5,567
Huang Ho (Yellow) Gulf of Chihli 2,900 4,667
Yenisei Arctic Ocean 2,800 4,506
Paraná Río de la Plata 2,795 4,498
Irtish Ob River 2,758 4,438
Zaire (Congo) Atlantic Ocean 2,716 4,371
Heilong (Amur) Tatar Strait 2,704 4,352
Lena Arctic Ocean 2,652 4,268
Mackenzie Beaufort Sea (Arctic Ocean) 2,635 4,241
Niger Gulf of Guinea 2,600 4,184
Mekong South China Sea 2,500 4,023
Mississippi Gulf of Mexico 2,348 3,779
Missouri Mississippi River 2,315 3,726
Volga Caspian Sea 2,291 3,687
Madeira Amazon River 2,012 3,238
Purus Amazon River 1,993 3,207
São Francisco Atlantic Ocean 1,987 3,198
Yukon Bering Sea 1,979 3,185
St. Lawrence Gulf of St. Lawrence 1,900 3,058
Rio Grande Gulf of Mexico 1,885 3,034
Brahmaputra Ganges River 1,800 2,897
Indus Arabian Sea 1,800 2,897
Danube Black Sea 1,766 2,842
Euphrates Shatt-al-Arab 1,739 2,799
Darling Murray River 1,702 2,739
Zambezi Mozambique Channel 1,700 2,736
Tocantins Pará River 1,677 2,699
Approx. length
7. Discharge
River m^3/sec mm/yr
% of total
entering
oceans
Runoff
Ratio
1 Amazon, Brazil 190,000 835 13.0 0.47
2 Congo, Zaire 42,000 340 2.9 0.25
3 Yangtse Kiang, China 35,000 560 2.4 0.50
4 Orinoco, Venezuela 29,000 845 2.0 0.46
5 Brahmaputra, Bangladesh 20,000 1070 1.4 0.65
6 La Plata, Brazil 19,500 235 1.3 0.20
7 Yenissei, Russia 17,800 215 1.2 0.42
8 Mississippi, USA 17,700 175 1.2 0.21
9 Lena, Russia 16,300 210 1.1 0.46
10 Mekong, Vietnam 15,900 630 1.1 0.43
11 Ganges, India 15,500 455 1.1 0.42
12 Irrawaddy, Burma 14,000 1020 1.0 0.60
13 Ob, Russia 12,500 135 0.9 0.24
14 Sikiang, China 11,500 840 0.8 -
15 Amur, Russia 11,000 190 0.8 0.32
16 St. Lawrence, Canada 10,400 310 0.7 0.33
The World’s Largest Rivers by Discharge
14. 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.
16. Discharge – the volume of water
moving past a given point in a certain
amount of time.
• Highly variable in most streams.
• When discharge increases, velocity and
channel cross-sectional area both increase.
Discharge (m3
/s) = channel
width(m) X channel depth(m) X
velocity(m/s)
19. 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!!!
22. 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.
23. 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.
24. How Do Streams Transport Eroded
Sediments to Deposit New Geologic
Formations?
• Types of Stream
Load:
– Dissolved Load
– Suspended
Load
– Bed Load
• Streams transport sediment via stream
loads.
27. – Capacity – the maximum load a stream can transport.
– Competence
• Indicates the maximum particle size a stream can transport.
• Determined by the stream’s velocity.
29. 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.
30. 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.
31. 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.
33. 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
34. • Factors that increase
downstream
– Velocity
– Discharge
– Channel Size
Changes from Upstream to Downstream
• Factors that decrease
downstream
– Gradient
– Channel Roughness
35. 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.
36. The Drainage Systems of Youthful
Streams End at the Base of the
Mountains Where Alluvial Fans are
Deposited.
37. • 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.
Alluvial Fans
Transition from Drainage to Transport Systems
39. 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.
40. Transport System
Mature Streams: Meandering Rivers
• 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.
43. Transport System
Mature Streams: Meandering Rivers
• Features of mature streams often include:
• Meanders
– Cut Banks and
Point Bars
– Cutoffs and
Oxbow Lakes
67. 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
68. • Deltas – Form when a stream enters an
ocean or lake.
• Characteristic of mature streams.
Distributary System: Deltas
• Consists of three
types of beds:
– Foreset Beds
– Topset Beds
– Bottomset Beds
71. 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.
72. 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)
73. 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
75. 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.
77. Drainage Patterns
• Pattern of the interconnected
network of streams in an area
– Common drainage patterns
• Dendritic
• Radial
• Rectangular
• Trellis
79. 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
81. 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
82. Rejuvenated Streams
• Terraces
– Remnants of a former floodplain.
– River has adjusted to a relative drop in base
level by downcutting.
84. Floods and Flood Control
• Floods are the most common and
most destructive geologic hazard
– Causes of Flooding:
• Naturally occurring factors
• Human-induced factors
85. Floods and Flood Control
• Types of Floods
– Regional Floods
– Flash Floods
– Ice-Jam Floods
– Dam Failure
– Levee Breach
95. 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
102. New Orleans Levee System
http://www.nola.com/katrina/graphics/flashflood.swf
103. Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
http://www.nrdc.org/water/pollution/fanacost.asp
• 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.
104. Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
http://www.nrdc.org/water/pollution/fanacost.asp
• 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 ever-
increasing flows of sewage
and polluted runoff into the
Anacostia.
A river designated for swimming,
fishing, and other recreation is
instead an eyesore, as this floating
debris testifies.
105. Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
http://www.nrdc.org/water/pollution/fanacost.asp
• 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.
106. Pollution and the Anacostia River:
One of the Nation’s Most Polluted
Rivers is in our Backyard
http://www.nrdc.org/water/pollution/fanacost.asp
• 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.
The District of Columbia's century-
old 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.
Editor's Notes
Begins as sheetflow:
Infiltration capacity is controlled by:
Intensity and duration of rainfall
Prior wetted condition of the soil
Soil texture
Slope of the land
Nature of the vegetative cover
