rivers!!!!!!!! (and valleys)

RIVERS!!!!!!!!(and valleys)

Chapter 12 (page 39)

http://www.youtube.com/watch?v=Xtk_bqkfeyE

Because Bill Nye always makes things better…

A drainage basin (watershed, catchment) is a piece of land where water (rain and melting ice) drains into a larger body of water. Includes the streams, rivers and channels OPEN SYSTEM separated by divides

When water accumulates upland, and flows along a definite course, they are called streams

Small streams tributary streams

Tributary streams flow down and join together to connect to a river

Drainage Basins, Streams, Rivers

Drainage Basin

The hardness of the rock layers in the region determines the formation of certain drainage pattern that results

There are three types of drainage patterns

Types of drainage patterns

Most common pattern

Resembles vein or tree branch pattern

Forms on flat surfaces where the rock layers are of uniform hardness

Form in v-shaped valleys where many small tributaries join together and then join onto a main river, giving it the appearance of a tree

Drainage pattern #1: Dendritic

As a river flows down a valley, smaller tributaries flow into it from steep mountain slopes

Tributaries enter the main river at approximately 90 degree angles, causing a trellis-like appearance of the drainage system

Trellis drainage is characteristic of areas with alternating parallel valleys and ridges, and folded mountains

Drainage pattern #2: Trellis

The streams radiate equally outwards from a central high point

Volcanoes (as well as domes and laccoliths Cone-shaped mountains) usually display excellent radial drainage

Drainage pattern #3: Radial

Dry (arid) regions steep slope forms canyons

(vertical erosion) Wet regions gentle slope heavy sediments in

water

(vertical erosion)

River Valley shapes

Youth stage

Mature stage

Old age stage

Rejuvenated stage

http://www.youtube.com/watch?v=AjZLAw_lgZ4&feature=related

Four stages of a River development

River cuts a deep V-shaped valley (steep gradient)

Flows in highlands of mountainous areas with very little shifting of its channel

Usually small in size

Dominated by erosion fast, violent water little deposition

Little floodplain, but rapids, waterfalls, and boulders may be found

Stage #1: Youth Stage

Receives the waters of many tributaries River increases in size and slows in velocity more

deposition Eroded the bed downward and gotten closer to the base level Though it is still eroding downwards, it mainly erodes

laterally to form meanders and eventually flood plains

Stage #2: Mature Stage

Extensive meandering forms oxbow lakes

Its gradient and speed are very slow,

Because of this it has lost the power to erode downwards and carry as much sediment load deposits rich alluvium on the floodplain

http://www.igeography.ie/mature-stage.html

Stage #3: Old Age stage

River returns to the youthful stage

Vertical erosion creates v-shaped valley and process starts again

Stage #4: Rejuvenated stage

http://www.slideshare.net/Dannyoc/stages-of-a-river

The four stages

THIS SHOULD BE FAMILIAR!!!

Hydraulic action

Abrasion

Attrition

Corrosion

Erosional action of rivers (4 types)

THIS SHOULD BE FAMILIAR!!!

Solution Suspension Saltation Traction

http://library.thinkquest.org/28022/transport/index.html

Ways that rivers transport sediments

Rivers PART TWO!!

Steep gradient (steep slope)

Water flows swiftly with vertical erosion

Waterfalls occur where rocks have eroded quickly

Igneous rock wears out much slower than others (e.g. sedimentary rock)

Landforms associated with upland rivers

Potholes develop along river beds

Pebbles get trapped Water spins and

abrasion deepens the hole

Eventually a gorge or even a canyon may result (narrow slot in landscape)

Potholes, Gorges and Canyons

When the river has reached an elevation close to the sea level, a flood plain may result

Lateral erosion and energy

River can flow overflow and deposit rich alluvium (ideal for farming)

Landforms associated with lowland rivers

Erosion is greatest and fastest along the outer edge of a meander (bend)

Undercut bank (outer edge)

Point bar/ slip-off slope (inner bank)

Meanders, undercut banks and slip-off slopes

Levees: mounds of sediment that slowly build up along the river bank

Hold in flood waterNatural dikesCommon in valleys where

river cannot carry all of its load

• Dikes: artificial levees created to minimize flooding

Levees and dikes

Mississippi River floods of 1993

Lowland regions sometimes uplift and the meandering river begins vertical erosion again

Once uplifting stops and a flood plain is formed, lateral erosion is once again dominant

The old, uplift flood plain sits high above river banksThese ledges are called river terraces

Let’s draw it out!!!

River terraces

Sand and gravel “islands” may break up the water flow, so rivers take on a braided appearance

Transport large volumes of debris when deposited, creates sand bars and islands

Braided river channels

A river carries sediment from its drainage basin into the ocean

Current carries them into the ocean before they are deposited

Sand (heavy) silt clay (light)

Large rivers have broad deltas with shallow water extending far into the sea

Very gentle slopeWaves cannot erode as effectively

River deltas

Arcuate delta

Bird’s foot delta

Estuarine delta

LOOK ON PAGE 190 OF BLUE GEOGRAPHY BOOK FOR AWESOME ILLUSTRATIONS FO DELTAS AROUND THE WORLD!!!

3 main types of delta

Carries water and sediment across a symmetrical delta in distributaries

Inverted cone shape

EX. Nile River Delta

Arcuate delta

Many distributary channels branch out from main river channel

Bird’s foot shape

EX. Mississippi River Delta

Bird’s foot delta

Forms when river sediment is deposited in a submerged river mouth

Estuary shape

Estuarine delta