tvc fluvial processes

34
River/ Fluvial Processes 1. Erosion, Transportation and Deposition in the River 2. Different River Landforms along the river

Upload: taka-geo

Post on 13-May-2015

1.472 views

Category:

Education


0 download

DESCRIPTION

Fluvial

TRANSCRIPT

Page 1: Tvc fluvial processes

River/ Fluvial Processes 1. Erosion, Transportation and Deposition in

the River

2. Different River Landforms along the river

Page 2: Tvc fluvial processes

Fluvial Processes

ElementsGravity

Water

Sediment

Topography

ProcessesErosion

Transportation

Deposition

OutputsLandforms (e.g. deltas, v-shaped valleys, islands, ox-bow lakes

Page 3: Tvc fluvial processes

A. EROSION

A river can erode material from its bed and banks Fluvial erosion occurs where a river is flowing fast, so it has a lot of energy to erode the bed and banks of the river. This mainly occurs in the upper portion of the river. This occurs in 3 different ways:

AbrasionHydraulic Action andAttrition

Page 4: Tvc fluvial processes

• Abrasion – Moving water throws particles it is carrying against the bed and banks of the river which then dislodges more material

• Hydraulic Action - The sheer force of the water

pounding into the bed and banks can dislodge material

• Attrition - Particles being carried downstream knock against each other, wearing each other down. This results in smaller, rounder particles as you move downstream

Page 5: Tvc fluvial processes

B. Methods of Transportation Fluvial transportation mainly occurs in the mid section of the river. Rivers transport larger material (e.g. rocks) where they have the most energy and smaller material (e.g. ash0 where they have the least energy. This occurs in four main ways:

SolutionSuspensionSaltationTraction

Page 6: Tvc fluvial processes

• Solution - Some minerals (particularly in limestone areas) dissolve easily in water and are not visible to the naked eye and are carried ‘in solution’ downstream

• Suspension – As the speed or velocity of a river increases, it is able to pick up and carry larger and larger particles in its flow. Where particles are carried along in the flow and are not in contact with the river bed, they are said to be travelling in suspension.

Page 7: Tvc fluvial processes

• Saltation - Heavier particles may not be held in the flow all the time but may be bounced along the bed

• Traction - The heaviest particles (eg boulders) cannot be carried so are rolled along the river bed. Such particles may only be moved when the river has a large volume of water in it

Page 8: Tvc fluvial processes

C. Deposition

This occurs in a river when the kinetic energy is LOW. This means the river speed is slow and therefore the flow cannot carry the particles any longer. This takes place mainly at the base of the river where it is wide and slow.

Page 9: Tvc fluvial processes

Landforms Created

There are different landforms created at each section of the river, as different processes dominate

UPPER COURSE: Narrow channel, fast moving, EROSION dominatesMIDDLE COURSE: Medium channel, medium speed, TRANSPORT

DOMINATESLOWER COURSE: Wide channel, slow moving, DEPOSITION dominates

Page 10: Tvc fluvial processes
Page 11: Tvc fluvial processes

Upper Course Landforms

Here the river is fast flowing but there is little water and load so does not have the power to erode the hillsides. Instead it erodes downwards to create v-shaped valleys

e.g. Whakapapaiti River

Page 12: Tvc fluvial processes

Middle Course Landforms

Here the river is wider and less steep. This means there is a greater volume of water allowing the river to erode sideways. This creates meanders which can change the course of the river and ox-bow lakes.

Page 13: Tvc fluvial processes

Lower Course Landforms

The river is at its widest and slowest at this point. This drop in energy means that deposition dominates forming braided channels and deltas.

Braided channel Delta

Page 14: Tvc fluvial processes
Page 15: Tvc fluvial processes
Page 16: Tvc fluvial processes
Page 17: Tvc fluvial processes
Page 18: Tvc fluvial processes
Page 19: Tvc fluvial processes

It’s your turn …• Draw a simple diagram

to represent each process within the river

• Solution =

• Suspension =

• Saltation =

• Traction =

Page 20: Tvc fluvial processes

River Features• Rivers are eroding, transporting and depositing

constantly within the drainage basin system.

• The river can be divided into 3 sections

• Upper Course at the Source,

• Middle Course

• Lower Course at the Mouth of the river.

• The river displays different characteristics at each section

Page 21: Tvc fluvial processes

Fluvial (River) Processes

1. Fluvial processes create landforms.

2. These processes are affected by specific factors.

Page 22: Tvc fluvial processes

Also known as ‘Torrent’ or ‘Youth’ stages

Interlocking Spurs

In the Upper Course, the river is fast flowing, but there is little water and load. The river is often called a stream and does not have the erosive power to remove the hillsides (spurs), but erodes downwards instead.

EROSION TYPE: Vertical and Headward

Page 23: Tvc fluvial processes

The river flows through the Spurs

Page 24: Tvc fluvial processes

Potholes

Boulders broken off by erosion that sit on the river bed create swirling eddy currents as the water flows past as the river is not

strong enough yet to move the boulders by TRACTION. These eddies swirl the boulder round and erode a pothole in the river

bed by ABRASION.

EROSION TYPE: Vertical

( by EDDY CURRENTS )

Page 25: Tvc fluvial processes

Waterfall

and Gorge 2

(PROFILE VIEW)EROSION

TYPE: Vertical and Headward

Page 26: Tvc fluvial processes
Page 27: Tvc fluvial processes

Meanders are formed because the current swings to the outside of a bend and concentrates the erosion there. Deposition occurs on the inside of the bed where there is not enough energy to carry load.

EROSION TYPE: Lateral

Also known as the ‘Mature’ stage Meanders 1

(Aerial View)

Page 28: Tvc fluvial processes

Meanders 2

(Profile View / Cross Section X - Y)

EROSION TYPE: Lateral

This cross section clearly shows the eddy current (near ’X’) formed by the velocity of the river being concentrated

on the outside of the bend. These UNDERCUT the bank causing the formation of a RIVER CLIFF. On the inside

(NEAR ‘Y’), a SLIP-OFF-SLOPE is formed where current is too slow to carry any load.

Page 29: Tvc fluvial processes

Ox-Bow Lake 1

(Aerial View)

EROSION TYPE: Lateral

Ox-bow lakes are formed when two meander RIVER CLIFFS are being

eroded towards each other. These will eventually meet,

causing the river to then flow across the

bottom of the diagram.

Page 30: Tvc fluvial processes

Ox-Bow Lake 2 (Aerial View)

Page 31: Tvc fluvial processes

Braided Channels (Oblique Side View)

DEPOSITION FEATURE: no

erosion in the Lower

Course

In the Summer months, load is dropped by the low volume of low-energy water in the river. These build up to form

obstructions in the river and it divides up to flow around them. In the winter, it is likely that the river volume will increase and

remove these obstructions.

Page 32: Tvc fluvial processes

Delta (Aerial View)

This deposition feature is one of the largest. When the flowing river hits the

non-flowing sea, energy is suddenly lost. This causes all of the load in the river

to drop in the river MOUTH. This builds up over time to create a delta – an area of land. The river divides into

DISTRIBUTARIES to continue to the sea, which

is now some way away from its original meeting

point.

Page 33: Tvc fluvial processes
Page 34: Tvc fluvial processes

Can you work out what the river

is trying to do by using the

information in this diagram?