CH. 9 - Running Water

Two sources of energy:

1) Internal energy - heat from core & radioactivity

Powers:a) EQ’sb) Volcanoesc) Mountain building

Two sources of energy:

2) Solar energy

Powers:

a) ocean circulation

b) weather & climate

c) hydrologic cycle

Hydrologic Cycle

Includes: - running water- ground water - glaciers- atmosphere (water vapor)

Distribution of Earth’s Water

97% ocean water

3% freshwater/brackish water

(Fig. 9.1)

Running Water (Streams) = 0.0001% of hydrosphere

Function of streams is to drain the land

- 36,000 km3 water drains annually

- single most important agent changing landscape

Running Water

Source is precipitation (ppt.)

~25% total ppt. becomes surface water

- depends on infiltration capacity

Infiltration capacity depends on:

1)

2)

3)

4)

5)

Drainage Basin

Total land area drained by river and its tributaries

Tributary = smaller stream flowing into a larger stream

Ex: Kickapoo Creek into IL River

Drainage Basin

Mississippi River = 3,222,000 km2

Amazon River = 5,778,000 km2

Drainage Basins

Empty into oceans

Exception: Great Basin in Nevada

- internal drainage basin (no streams flow out)

Drainage Divide

High point dividing adjacent drainage basins

Ex: Continental Divide in Rocky Mtns.

Stream Order

First-order = streams with no tributaries

Second-order = two first-order streams unite

(only first-order streams as tributaries)

Stream Order

Third-order = two second-order streams unite

- can have first- and second-order streams as tributaries

Streams

Three main areas:

- zone of erosion

- zone of sediment transport

- zone of deposition

Streams

Ability to erode/deposit material is function of its velocity

Velocity = rate of flow = meters

second

Stream Velocity Factors:

1) Gradient – slope of stream channel

Slope = rise

run

= amount of elevation change

distance measured

Gradient

Varies considerably from:

a) one stream to another

b) along the course of any given stream

Ex: Gradient changes in Missouri River (maps in lab)

Stream Velocity Factors:

2) Channel characteristics

a) Shape – controls amount of water in contact with channel

Contact with channel causes velocity to (slow down, speed up).

Channel Characteristics

b) Size – larger channel is more efficient

Why?

Channel Characteristics

c) Roughness –sediment lining stream channel

Boulders = rough = more turbulent = slower

Clay/sand = smooth = faster

Stream Velocity Factors:

3) Discharge

Amount of water flowing past a certain point in a given time period

Stream Discharge

Discharge = channel x channel x velocity width depth

Discharge = meters x meters x meters second

Discharge = meters3 = cms second

Stream Discharge

Mississippi RiverDrainage basin = 3,222,000 km2

Discharge = 17,300 cmsAmazon River Drainage basin = 5,778,000 km2

Discharge = 212,400 cms

Stream Order

As stream order increases:

- discharge __________

- gradient __________

- velocity __________

- channel dimensions ________

Stream flow

1) Laminar flow – straight line

- indicates slow velocity or smooth stream channel

Stream flow

2) Turbulent flow

- indicates fast velocity or rough stream channel (rapids)

- increased erosion - more sediment in suspension

Longitudinal Profile

Cross-sectional view of a river from headwaters to mouth

Changes:a) Gradient decreases from head

to mouth b) Discharge increases towards

mouth of river

Base level

Lowest elevation a stream can erode down its channel

Ultimate base level = sea level

Local base level:

- lakes, resistant rock layers, larger streams, reservoirs

Base Level

Changes in base level causes changes in stream activities

Base Level

Ex 1: Building a dam

- creates new local base level

Changes upstream:

Changes downstream:

Base Level

Ex. 2: Draining a lake

- stream channel cuts down to the next local base level

Stream Transport

1) Bed load – material in contact w/channel bottom

- moves by sliding, rolling, saltation (jumping motion)

- moves intermittently

Stream Transport

2) Suspended Load - usually fine sand & clay-size

particles- visible sediment (muddy look of

rivers)- largest amount of material

carried by streams

Stream Transport

3) Dissolved Load

- invisible

- transported regardless of stream velocity

- precipitates only when stream chemistry changes

Dissolved Load

Measured in parts per million (ppm)

~4 billion metric tons supplied to oceans annually

Streams’ ability to erode/deposit depends on:

1) Capacity

- maximum amount of sediment stream can transport

- directly related to discharge (volume of water flowing)

Streams’ ability to erode/deposit depends on:

2) Competence – largest sediment size stream can move

- as velocity doubles, competence quadruples

Flood stages

Greatest power of streams to erode & transport material

Capacity:

Competence:

Types of stream channels

1) Braided

- channel crosses back & forth

- shallow stream channel with large sediment load

Braided streams

Sediment load is deposited quickly

Caused by:

a) abrupt decrease in gradient

b) decrease in discharge (drought)

Types of stream channels

2) Meandering

- river is confined to one channel

- river channel is curved

Curves = meanders

Alluvium

Stream-deposited sediment

- well-sorted by size

As velocity decreases, heaviest sediment is deposited first

Depositional Features

RapidsPoint barsFloodplainsNatural leveeBack swampYazoo tributary

Depositional Features

Delta

Alluvial Fan

Erosional Features

WaterfallsV-shaped valleysCutbanksMeandersMeander cutoffs Oxbow lakes

Erosional Features

Meander scar

Incised meander - meanders enclosed in steep valley walls

Stages of stream valley development

Stages of Stream Valley Development

Early stage:- stream is well above base level- downcutting is main erosional

work- narrow V-shaped valley w/no

floodplains

Early stage

- relatively straight course

- rapids & waterfalls may be common

Stages of Stream Valley Development

Middle stage:- stream closer to base level- lateral erosion is major

erosional work- floodplain created & enlarged

Middle stage

- meanders

- cutoffs & oxbows may be present

- floodplain defined by meander belt

Stages of Stream Valley Development

Late stage:- stream close to base level- very wide floodplain- primary erosional work =

reworking floodplain sediments

Late stage

- meanders, cutoffs, oxbows, meander scars

- natural levee is well developed

- backswamps, yazoo tributaries

Rejuvenated Stage

River near base level is uplifted

- downcutting dominates

- incised meanders

Ways to Lengthen Valleys:

1) Deposition at mouth of river

Ex: delta

2) Headward Erosion

- erosion cuts into upland area at the head of the river

Stream Piracy

Diversion of one stream channel by headward erosion of another stream

Stream Piracy

Two streams on opposite sides of a divide:

Stream w/ steeper gradient cuts headward faster

- cuts across divide and captures water from slower stream