Transcript RIVER STUDIES - GeoInteractive

RIVER
STUDIES
The Changes downstream
in a river valley
The Hydrologic Cycle
 Infiltration = Groundwater System
 Runoff = Surface Water System
Satellite view of river
drainage, Middle East
What is this
features?
Upper valley
characteristics
Upper valley
characteristics
Upper valley
characteristics
“V”shape valley,
vertical erosion
dominant
Upper valley
characteristics
“V”shape valley,
vertical erosion
dominant
Interlocking spurs
Upper valley
characteristics
“V”shape valley,
vertical erosion
dominant
Interlocking spurs
Slumping and
landslides very active hill
slopes
Upper valley
characteristics
“V”shape valley,
vertical erosion
dominant
Interlocking spurs
Slumping and
landslides very active hill
slopes
Narrow, shallow
channel, low
velocity and
discharge
Upper valley
characteristics
“V”shape valley,
vertical erosion
dominant
Interlocking spurs
Slumping and
landslides very active hill
slopes
Narrow, shallow
channel, low
velocity and
discharge
Large bed
load derived
from
upstream and
from valley
sides
Interlocking spurs,
Robinson, Lake District
A typical upper
course valley with
interlocking spurs,
steep valley sides
and active slope
processes
River load in upper course
Why are they rounded?
Boulders are large and semi-rounded, due to
attrition within the load and abrasion with
the stream bed and banks
Rapids in the Upper Tees
Valley
WHAT IS A RAPID?
High Force waterfall, R.
Tees
WHAT IS A
WATERFALL?
High Force waterfall, R.
Tees
Waterfall creates
gorge as it
recedes
upstream by
eroding the base
and neck
HOW IS A
GORGE
FORMED?
What is this
feature called?
Plunge pool
Waterfall formation
Look at the diagram, How is a waterfall formed?
High Force Waterfall R.
Tees
Close-up of potholes
How are these formed?
Potholes, human scale!!
Erosion Processes
Abrasion (Corrasion) -
Corrosion Attrition Hydraulic Action -
 is when the river is loaded with material in suspension
and scours away at the river banks. (Sandpaper
effect)
 is the shear force of the river impacting on the sides of
the river banks.
 is substances carried in solution such as acids. They
dissolve rocks away over long periods of time.
 is when bed load collides into each other with the
current flow and breaks down into smaller particles.
Middle course, R. Tees
HOW DOES THIS DIFFER FROM
THE UPPER SECTION?
Middle course, R. Tees
WHAT DO YOU THINK THE
ARROWS POINT TO?
Valley opens out,
more gentle
slopes, wider
valley bottom
First signs of
meanders
River channel
wider, deeper,
greater velocity
and discharge
Meandering Rivers
WHAT IS A MEANDER?
Formation of Meanders
Point
bar
deposits
Point Bar Deposits
Point bar deposits grows laterally
through time
Meander, R. Lavant,
Chichester
Meander, R. Lavant,
Chichester
WHICH WAY IS THIS
MEANDER MOVING?
WHAT DO THE ARROWS
POINT TO?
Floodplain
Slip-Off Slope
Point bar deposits on the inner meander bend
where there is low energy
River Cliff
WHERE IS EROSION
TAKING PLACE?
Cut bank erosion (River Cliff)
F
A
E
B
Point
bar
deposits
C
}
Meander
loop
D
WHERE IS DEPOSTION TAKING
PLACE?
Meander on the R.
Colorado
WHY IS DEPOSITION OCCURING
HERE?
How did
these
meanders
form?
REVISION: What River features do you
get here?
Migrating meanders, R.
Gongola, Nigeria
WHY ARE THEY MIGRATING?
What happens to the river
when it moves to the middles
course
 Gradient becomes less steep
 River continues to erode vertically but
LATERAL erosion now occurs in
MEANDERS
 What is MEANDER MIGRATION ?
 Name three effects it have on the valley?
 What factors effect how much load is
being carried?
Transportation
 What are the four methods of transportation?
 Traction - is when large particles roll along the river
bed
 Saltation - is when smaller particles bounce and
collide in a leapfrog manner across the river bed.
 Suspension - is when the river holds even smaller
particles and carries them in its current. This is when
the river appears to be murky.
 Solution - is when dissolved material is carried.
Lower Course: Severn
Valley
Lower Severn Valley
Very wide
floodplain
Well developed
meanders with
bars in the channel
indicating high
Very gentle valley
sediment load
side gradients
HOW DOES IT DIFFER FROM THE MIDDLE
COURSE?
Flood Plains
HOW DO YOU THINK THE
TERRACES WERE FORMED?
The entire floodplain can become
covered with water during floods.
Ox Bow Lake Formation
LOOK AT THE DIAGRAM & EXPLAIN THERE
FORMATION
Formation of an Oxbow
Ox Bow lake on
Mississippi
Levee formation
Levees
WHAT DO YOU THING HUMANS MIGHT HAVE
DONE TO THIS LEVEE?
Delta Formation
WHAT IS A DELTA?
DEPOSITON OF MATERIAL BY THE RIVER
WHEN IT ENTERS THE SEA
WHY DOES IT DROP ITS SEDIMENT
Mississippi Delta from
Space
MISSISSIPPI
The Nile Delta from space
River Nile
Estuary Formation
HOW DOES THIS DIFFER FROM A
DELTA?
RAISED VALLEY SIDES
USING YOUR ATLAS
FIND AN ESTUARY
(LOOK AT THE RIVER THAMES)
The Lower
Course of a
river valley
has been
DROWNED
by a rise in
sea level or
a fall in the
land level.
The Rhone Delta
USING YOU ATLAS
LOCATE THE RHONE
DELTA
The Rhone Delta S. France
Look at p39 and identify the
KEY FEATURES CAN YOU
SEE IN THE SATELLITE PHOTO?
The Rhone Delta
WHY HAS A DELTA
FORMED HERE? LOOK AT P 39
Summary of valley
characteristics
Upper


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
Middle
 Wider valley
 Gentler valley sides
 Meanders
Lower
 Widest part of valley
 Floodplain
 Terraces
 Ox Bow & Levees
 Delta, Estuary
Interlocking spurs
“V” shaped valley
Waterfall
Gorge
The River Tees
TRY AND FIND THE RIVER TEES
IN YOUR ATLAS
HINT LOOK AT THE MAP
Land Use in Drainage Basin
of River Tees
WHAT IS THE AREA IN EACH BOX?
Upper Tees
COW GREEN RESERVOIR
WHAT HUMAN INFLUENCES EXIST IN THE MAPS?
The Upper Tees Cronkley
Scar
WHAT ARE THE KEY GEOGRAPHCIAL FEATURES
YOU CAN SEE IN THE PHOTOGRAPH
MOORLAND
STEEP VALLEY
TURBULENT RIVER
CHANNEL
SLOPE DEBRIS
WHAT LAND USES CAN YOU SEE IN THE
PHOTO?
Upper Tees
WHAT IS THE NAME OF THE
WATERFALL?
The Lower Course Tees
FLAT VALLEY FLOOR
URBAN
SETTLEMENT
WIDE MEANDERS
HOW HAS THE RIVER AND
LAND USE CHANGED?
The
Lower Tees
TEESMOUTH
ESTUARY
WHAT LAND USE CAN YOU SEE IN THE
PHOTOGRAPH?
The River meets the Sea
River Management
WHAT IS THE FUNCTIONOF THE BARRAGE?
LOOK AT P42
WHAT DO YOU THINK
THE PHOTOS SHOW?
Formation of the
Mississippi River Delta
More recent delta
Modern
sediments
delta
Early delta
Causes of Floods
 A Flood can occur when a river exceeds its bank full stage and water will subsequently inundate the
adjacent surrounding area.
 Heavy rainfall - long periods of heavy rainfall will lead to an
increase in surface runoff and increase in river level.
 Snow melt and heavy rainfall - water in storage may be freed by
Spring melts increasing surface runoff.
 Deforestation - cutting down of trees leads to a reduction in
interception rates and an increase in surface runoff. This may also
lead to rapid erosion rates due to a lack of stability in the soil
subsurface.
 Urbanisation - tarmac and concrete surfaces are impermeable
and lead to an increase in surface runoff.
Flood Control and Management
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There are a number of ways managing floods:
1. Afforestation - planting trees increases interception rates and reduces
surface runoff.
2. Dams and Reservoirs - these hold back and regulate the flow of river
water. Can be used as fresh water supply and generation of HEP.
3. Diversion Channels - overflow channels which take surplus water out
of a river in times of flood.
4. Channel Straitening and Dredging - smoothens the channel to
increase the speed (velocity) of the river and get water out of the drainage
basin as quickly as possible.
5. Artificial Levees - makes river banks higher therefore holding more
water.
6. Culverts - semi circular, smooth channels increase velocity and gets
water away from urban areas as quickly as possible.
7. Revetments and Channel Walls - strengthen river banks from
erosion.