The Changes downstream

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RIVER STUDIES

• The Changes downstream
• in a river valley

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The Hydrologic Cycle

• Infiltration Groundwater System

• Runoff Surface Water System

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Satellite view of river drainage, Middle East
What is this features?
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Upper valley characteristics
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Upper valley characteristics
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Upper valley characteristics
Vshape valley, vertical erosion dominant
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Interlocking spurs
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Interlocking spurs
Slumping and landslides - very active hill
slopes
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Narrow, shallow channel, low velocity and
discharge
Interlocking spurs
Slumping and landslides - very active hill
slopes
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Narrow, shallow channel, low velocity and
discharge
Interlocking spurs
Slumping and landslides - very active hill
slopes
Large bed load derived from upstream and from
valley sides
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Interlocking spurs, Robinson, Lake District
A typical upper course valley with interlocking
spurs, steep valley sides and active slope
processes
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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
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Rapids in the Upper Tees Valley
WHAT IS A RAPID?
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High Force waterfall, R. Tees
WHAT IS A WATERFALL?
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High Force waterfall, R. Tees
Waterfall creates gorge as it recedes upstream by
eroding the base and neck
What is this feature called?
HOW IS A GORGE FORMED?
Plunge pool
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Waterfall formation
Look at the diagram, How is a waterfall formed?
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High Force Waterfall R. Tees
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Close-up of potholes
How are these formed?
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Potholes, human scale!!
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Erosion Processes
Corrosion -
Attrition -
Abrasion (Corrasion) -
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.

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Middle course, R. Tees
HOW DOES THIS DIFFER FROM THE UPPER SECTION?
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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
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Meandering Rivers
WHAT IS A MEANDER?
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Formation of Meanders
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Point bar deposits
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Point Bar Deposits
Point bar deposits grows laterally through time
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Meander, R. Lavant, Chichester
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Meander, R. Lavant, Chichester
WHAT DO THE ARROWS POINT TO?
WHICH WAY IS THIS MEANDER MOVING?
Floodplain
Slip-Off Slope
River Cliff
Point bar deposits on the inner meander bend
where there is low energy
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WHERE IS EROSION TAKING PLACE?
Cut bank erosion (River Cliff)
F
A
E
B
Point bar deposits

Meander loop
C
D
WHERE IS DEPOSTION TAKING PLACE?
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Meander on the R. Colorado
WHY IS DEPOSITION OCCURING HERE?
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How did these meanders form?
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REVISION What River features do you get here?
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Migrating meanders, R. Gongola, Nigeria
WHY ARE THEY MIGRATING?
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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?

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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.

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Lower Course Severn Valley
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Lower Severn Valley
Very wide floodplain
Well developed meanders with bars in the channel
indicating high sediment load
Very gentle valley side gradients
HOW DOES IT DIFFER FROM THE MIDDLE COURSE?
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Flood Plains
HOW DO YOU THINK THE TERRACES WERE FORMED?
The entire floodplain can become covered with
water during floods.
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Ox Bow Lake Formation
LOOK AT THE DIAGRAM EXPLAIN THERE FORMATION
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Formation of an Oxbow
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Ox Bow lake on Mississippi
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Levee formation
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Levees
WHAT DO YOU THING HUMANS MIGHT HAVE DONE TO THIS
LEVEE?
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Delta Formation
WHAT IS A DELTA?
DEPOSITON OF MATERIAL BY THE RIVER WHEN IT
ENTERS THE SEA
WHY DOES IT DROP ITS SEDIMENT
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Mississippi Delta from Space
MISSISSIPPI
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The Nile Delta from space
River Nile
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Estuary Formation
HOW DOES THIS DIFFER FROM A DELTA?
The Lower Course of a river valley has been
DROWNED by a rise in sea level or a fall in the
land level.
RAISED VALLEY SIDES
USING YOUR ATLAS FIND AN ESTUARY (LOOK AT THE
RIVER THAMES)
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The Rhone Delta
USING YOU ATLAS LOCATE THE RHONE DELTA
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The Rhone Delta S. France
Look at p39 and identify the KEY FEATURES CAN
YOU SEE IN THE SATELLITE PHOTO?
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The Rhone Delta
WHY HAS A DELTA FORMED HERE? LOOK AT P 39
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Summary of valley characteristics
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The River Tees
TRY AND FIND THE RIVER TEES IN YOUR ATLAS HINT
LOOK AT THE MAP
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Land Use in Drainage Basin of River Tees
WHAT IS THE AREA IN EACH BOX?
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Upper Tees
COW GREEN RESERVOIR
WHAT HUMAN INFLUENCES EXIST IN THE MAPS?
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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?
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Upper Tees
WHAT IS THE NAME OF THE WATERFALL?
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The Lower Course Tees
FLAT VALLEY FLOOR
URBAN SETTLEMENT
WIDE MEANDERS
HOW HAS THE RIVER AND LAND USE CHANGED?
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The Lower Tees
TEESMOUTH ESTUARY
WHAT LAND USE CAN YOU SEE IN THE PHOTOGRAPH?
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The River meets the Sea
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River Management
WHAT IS THE FUNCTIONOF THE BARRAGE?
LOOK AT P42 WHAT DO YOU THINK THE PHOTOS SHOW?
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Formation of the Mississippi River Delta
More recent delta sediments
Modern delta
Early delta
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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.

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Flood Control and Management

• 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.