CHAPTER 16SURFACE 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

• Infiltration = Groundwater System• Runoff = Surface Water System• Runoff = Precipitation – Evapotranspiration

Figure 16.3

Where is the Water ?

Figure 16.2

The World’s Largest Rivers

by Length

Largest Rivers of the World   

River Outflow mi. kmNile 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

Discharge

River m 3̂/sec mm/yr % of total entering oceans

Runoff Ratio

1 Amazon, Brazil 190,000 835 13.0 0.472 Congo, Zaire 42,000 340 2.9 0.253 Yangtse Kiang, China 35,000 560 2.4 0.504 Orinoco, Venezuela 29,000 845 2.0 0.465 Brahmaputra, Bangladesh 20,000 1070 1.4 0.656 La Plata, Brazil 19,500 235 1.3 0.207 Yenissei, Russia 17,800 215 1.2 0.428 Mississippi, USA 17,700 175 1.2 0.219 Lena, Russia 16,300 210 1.1 0.4610 Mekong, Vietnam 15,900 630 1.1 0.4311 Ganges, India 15,500 455 1.1 0.4212 Irrawaddy, Burma 14,000 1020 1.0 0.6013 Ob, Russia 12,500 135 0.9 0.2414 Sikiang, China 11,500 840 0.8 -15 Amur, Russia 11,000 190 0.8 0.3216 St. Lawrence, Canada 10,400 310 0.7 0.33

The World’s Largest Rivers by Discharge

U.S. Precipitation Map

U.S. Runoff Map

Notice the effect of the Rocky Mountains

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?

• Laminar Flow

• Turbulent Flow

• By Stream Flow – Two types determined primarily by velocity:

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.

• 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)

- Velocity measurements V

0.6D

D

Pygmy Meter Price Meter

A

dAVQ

Stream bank

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?

• Types of Stream Load:– Dissolved Load– Suspended

Load– Bed Load

• Streams transport sediment via stream loads.

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 ProfileCan 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

• Factors that increase downstream– Velocity– Discharge– Channel Size

Changes from Upstream to Downstream

• 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– 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 FansTransition from Drainage to Transport Systems

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 SystemMature 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.

Transport SystemMature Streams: Meandering Rivers

• Features of mature streams often include:• Floodplains

Animation #81: Stream Processes – Floodplain

Development

Transport SystemMature 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 streamflowing fromtop of screento bottom

Maximum erosion

Maximum deposition

Oxbow Lake

Oxbow cuttoff

Meander scars

Animation #83: Stream Processes – Floodplain

Development and Oxbow Lakes

Transport SystemMature 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

• 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

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 DoesGeology 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_flood.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

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.

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.

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.

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.