RIVER FORMATIONRIVER FORMATION

EARTH’S GRAVITATIONAL FORCE EARTH’S GRAVITATIONAL FORCE PULLS OBJECTS TOWARD IT’S CENTER PULLS OBJECTS TOWARD IT’S CENTER

OF MASS.OF MASS. WATER FALLING DOWN A SLOPE IS WATER FALLING DOWN A SLOPE IS

EVIDENCE OF GRAVITY.EVIDENCE OF GRAVITY. AS OBJECTS DROP TO EARTH’S AS OBJECTS DROP TO EARTH’S SURFACE, THEY PICK UP SPEED.SURFACE, THEY PICK UP SPEED.

WHEN WATER FALLS DOWN A SLOPE, WHEN WATER FALLS DOWN A SLOPE, IT PICKS UP SPEED.IT PICKS UP SPEED.

RIVER FORMATIONRIVER FORMATION

IT’S ENERGY OF MOTION IS IT’S ENERGY OF MOTION IS MUCH GREATER, AND IT CAN MUCH GREATER, AND IT CAN ERODE MORE QUICKLY THAN ERODE MORE QUICKLY THAN

SLOW MOVING WATER.SLOW MOVING WATER. IN THIS SECTION WE WILL LEARN IN THIS SECTION WE WILL LEARN

HOW A RIVER FORMS.HOW A RIVER FORMS.

FACTORS AFFECTING FACTORS AFFECTING RUNOFF OF WATERRUNOFF OF WATER

1. THE AMOUNT OF RAIN.1. THE AMOUNT OF RAIN. 2. THE TIME SPAN OVER WHICH 2. THE TIME SPAN OVER WHICH

THE RAIN FALLS.THE RAIN FALLS. 3. SLOPE OF THE LAND.3. SLOPE OF THE LAND.

4. THE AMOUNT OF VEGETATION.4. THE AMOUNT OF VEGETATION. 5. WHAT TYPE OF SOIL IT RUNS 5. WHAT TYPE OF SOIL IT RUNS

ACROSS.ACROSS.

RILL AND GULLY RILL AND GULLY EROSIONEROSION

RILL EROSION BEGINS WHEN A SMALL RILL EROSION BEGINS WHEN A SMALL STREAM FORMS DURING A HEAVY RAIN.STREAM FORMS DURING A HEAVY RAIN.

AS THIS STREAM FLOWS ALONG, IT HAS AS THIS STREAM FLOWS ALONG, IT HAS ENOUGH ENERGY TO CARRY AWAY PLANTS ENOUGH ENERGY TO CARRY AWAY PLANTS

AND SOIL.AND SOIL. THERE’S A SCAR LEFT ON THE SLOPE WHERE THERE’S A SCAR LEFT ON THE SLOPE WHERE

THE WATER ERODED THE PLANTS AND SOIL.THE WATER ERODED THE PLANTS AND SOIL. IF A STREAM FREQUENTLY FLOWS IN THE IF A STREAM FREQUENTLY FLOWS IN THE SAME PATH, RILL EROSION MAY TURN INTO SAME PATH, RILL EROSION MAY TURN INTO

GULLY EROSION.GULLY EROSION.

GULLY EROSIONGULLY EROSION

IN GULLY EROSION, A RILL CHANNEL IN GULLY EROSION, A RILL CHANNEL BECOMES BROADER AND DEEPER.BECOMES BROADER AND DEEPER.

LARGE AMOUNTS OF SOIL ARE REMOVED LARGE AMOUNTS OF SOIL ARE REMOVED TO FORM A GULLY.TO FORM A GULLY.

IF THE WATER CONTINUES TO FLOW IF THE WATER CONTINUES TO FLOW FREQUENTLY THROUGH THE GULLY, IT FREQUENTLY THROUGH THE GULLY, IT

WILL WIDEN AND DEEPEN EVEN FURTHER, WILL WIDEN AND DEEPEN EVEN FURTHER, EVENTUALLY FORMING A STREAM.EVENTUALLY FORMING A STREAM.

STREAM EROSIONSTREAM EROSION

SOMETIMES WATER CONTINUES SOMETIMES WATER CONTINUES TO FLOW ALONG A DEPRESSION.TO FLOW ALONG A DEPRESSION. IT THEN BECOMES A STREAM.IT THEN BECOMES A STREAM.

AS THE STREAM MOVES ALONG, AS THE STREAM MOVES ALONG, IT CONSTANTLY PICKS UP IT CONSTANTLY PICKS UP

SEDIMENTS FROM THE BOTTOM SEDIMENTS FROM THE BOTTOM AND SIDES OF IT’S CHANNEL.AND SIDES OF IT’S CHANNEL.

STREAM EROSIONSTREAM EROSION

WATER PICKS UP AND CARRIES SOME OF WATER PICKS UP AND CARRIES SOME OF THE LIGHTWEIGHT SEDIMENTS, WHILE THE LIGHTWEIGHT SEDIMENTS, WHILE

LARGE, HEAVY PARTICLES JUST ROLL ALONG LARGE, HEAVY PARTICLES JUST ROLL ALONG THE BOTTOM OF A STREAM CHANNEL.THE BOTTOM OF A STREAM CHANNEL.

ALL OF THESE DIFFERENT SIZED MATERIALS ALL OF THESE DIFFERENT SIZED MATERIALS SCRAPE AGAINST THE BOTTOM AND SIDES SCRAPE AGAINST THE BOTTOM AND SIDES OF THE CHANNEL, WHERE THEY CONTINUE OF THE CHANNEL, WHERE THEY CONTINUE

TO KNOCK LOOSE MORE SEDIMENTS.TO KNOCK LOOSE MORE SEDIMENTS. BECAUSE OF THIS, A STREAM CONTINUALLY BECAUSE OF THIS, A STREAM CONTINUALLY

CUTS A DEEPER AND WIDER CHANNEL.CUTS A DEEPER AND WIDER CHANNEL.

Valleys with Valleys with very steep, very steep,

almost almost vertical sides vertical sides

are called are called canyons or canyons or

gorges.gorges.

Rivers move a great deal of Rivers move a great deal of material. The faster the water material. The faster the water

moves, the larger material moves, the larger material that can be carried down that can be carried down

stream.stream.

Fast moving Fast moving upstream portionsupstream portions can often move rocks and can often move rocks and

boulders.boulders.

Downstream portionsDownstream portions usually only usually only transport small silts and clays.transport small silts and clays.

This process tends to sort This process tends to sort materials by size.materials by size.

Have you ever wondered why Have you ever wondered why we have so much silt and clay we have so much silt and clay

in our soil?in our soil?

Stream Velocity and Carrying Capacity• Fast moving water can carry larger sediments (duh)

The speed at which a stream flows will determine what size sediments it can

carry

Slow Fast

Big

Sm

all

RIVER SYSTEM RIVER SYSTEM DEVELOPMENTDEVELOPMENT

IF YOU HAVE A STREAM IN YOUR IF YOU HAVE A STREAM IN YOUR NEIGHBORHOOD, IT IS PART OF A NEIGHBORHOOD, IT IS PART OF A

RIVER SYSTEM.RIVER SYSTEM. THE WATER IN THE STREAM CAME THE WATER IN THE STREAM CAME FROM RILLS, GULLIES, AND SMALLER FROM RILLS, GULLIES, AND SMALLER

STREAMS LOCATED UPSTREAM.STREAMS LOCATED UPSTREAM. WHERE SMALL STREAMS JOIN, A WHERE SMALL STREAMS JOIN, A

LARGER STREAM FORMS.LARGER STREAM FORMS. FINALLY, THESE LARGER STREAMS FINALLY, THESE LARGER STREAMS MERGE, FORMING A LARGER BODY OF MERGE, FORMING A LARGER BODY OF

WATER CALLED A RIVER.WATER CALLED A RIVER.

A stream or river A stream or river can not cut its bed can not cut its bed any lower than the any lower than the body of water into body of water into

which it flows.which it flows.

As the stream As the stream approaches this approaches this basebase levellevel, the , the

slope and speed of slope and speed of the stream the stream decrease.decrease.

The river channel The river channel becomes wider, becomes wider, deeper, and the deeper, and the volume is bigger volume is bigger

as there are as there are more tributaries more tributaries contributing to contributing to

the volume.the volume.

The river valley The river valley also changes at also changes at

this point.this point.

It becomes more It becomes more open, more of a open, more of a U shape with a U shape with a

wider river floor.wider river floor.

The lower or The lower or downstream downstream

portionportion of the river of the river is at its deepest, is at its deepest,

widest and widest and slowest speed.slowest speed.

It also has the It also has the largest volume largest volume

and a very gentle and a very gentle gradient.gradient.

STAGES OF STREAM STAGES OF STREAM DEVELOPMENTDEVELOPMENT

THERE ARE MANY DIFFERENT THERE ARE MANY DIFFERENT TYPES OF STREAMS.TYPES OF STREAMS.

SOME ARE NARROW AND SWIFT SOME ARE NARROW AND SWIFT MOVING, AND OTHERS ARE VERY MOVING, AND OTHERS ARE VERY

WIDE AND SLOW MOVING.WIDE AND SLOW MOVING. STREAMS DIFFER BECAUSE THEY STREAMS DIFFER BECAUSE THEY

ARE IN DIFFERENT STAGES OF ARE IN DIFFERENT STAGES OF DEVELOPMENT.DEVELOPMENT.

STAGES OF STREAM STAGES OF STREAM DEVELOPMENTDEVELOPMENT

THESE STAGES DEPEND ON THE THESE STAGES DEPEND ON THE SLOPE OF THE GROUND OVER SLOPE OF THE GROUND OVER WHICH THE STREAM FLOWS.WHICH THE STREAM FLOWS.

STREAMS ARE CLASSIFIED AS:STREAMS ARE CLASSIFIED AS: 1. YOUNG1. YOUNG

2. MATURE2. MATURE 3. OLD3. OLD

STAGES OF STREAM STAGES OF STREAM DEVELOPMENTDEVELOPMENT

THE STAGES OF DEVELOPMENT THE STAGES OF DEVELOPMENT AREN’T ALWAYS RELATED TO THE AGE AREN’T ALWAYS RELATED TO THE AGE

OF A RIVER.OF A RIVER. THE NEW RIVER IN WEST VIRGINIA, THE NEW RIVER IN WEST VIRGINIA, FOR EXAMPLE, IS ONE OF THE OLDEST FOR EXAMPLE, IS ONE OF THE OLDEST

RIVERS IN NORTH AMERICA.RIVERS IN NORTH AMERICA. HOWEVER, IT HAS A STEEP VALLEY HOWEVER, IT HAS A STEEP VALLEY

AND CASCADES THROUGH RAGING AND CASCADES THROUGH RAGING RAPIDS AND, AS A RESULT, IS RAPIDS AND, AS A RESULT, IS

CLASSIFIED AS A YOUNG STREAM.CLASSIFIED AS A YOUNG STREAM.

Stream Development – Young Stream Development – Young StageStage

Steep V-Shaped Valley Steep V-Shaped Valley Rapids and Waterfalls Rapids and Waterfalls No Flood Plain No Flood Plain Fast, high energyFast, high energy

YOUNG streams flow over a steep gradient and tend to be relatively

small.

As they flow they carve

out a V-shaped valley

Waterfalls indicate a

YOUNG stream

Stream Development - Mature Stream Development - Mature

StageStage Lateral erosion widens the Lateral erosion widens the

valley profile – slope decreasesvalley profile – slope decreases River meanders pronounced River meanders pronounced A A FLOOD PLAINFLOOD PLAIN develops develops

As the stream grows larger – As the stream grows larger – it begins to shift its course in it begins to shift its course in a series of bends or curves a series of bends or curves

called meanders seeking out called meanders seeking out the lowest elevationthe lowest elevation

As time goes by, the stream erodes away the land and makes it flatter.

When the gradient is low, the shape of the stream changes and meanders form:

MEANDER

Stream Development - Old Stream Development - Old AgeAge

Very Wide Flood PlainVery Wide Flood Plain Land worn down to flat surface Land worn down to flat surface Many Meanders, Oxbow LakesMany Meanders, Oxbow Lakes

Eventually this

meander gets so big

and exaggerated that it

is ‘cut off ’ from the stream.However, the channel full of water is still

there, so it becomes an OXBOW LAKE

Levee FormationLevee Formation

Contour lines showing head of Contour lines showing head of the stream to the mouth of the stream to the mouth of

stream with deltastream with delta

Velocity slows when entering a large body of water

Eventually all streams flow into the ocean

This part of a stream is called a

DELTA

What is the correct sequence in stream development?