12River ProcessesA river process is something that happens in the river. The main processes in the river areErosion - where parts of the river bed and bank get eroded / removed from the landscapeTransportation - where the eroded material is carried from one place to another through the river systemDeposition - where the river load becomes too heavy for the river to carry and is dumped down / deposited.
13A river can erode material from its bed and banks in 4 main ways Abrasion – Moving water throws particles it is carrying against the bed and banks of the river which dislodges more materialHydraulic Action - The sheer force of the water pounding into the bed and banks can dislodge materialAttrition - Particles being carried downstream knock against each other, wearing each other down. This results in smaller, rounder particles as you move downstreamUse your text book to see if you can find the 4th type!
14Methods of ErosionAbrasion –Hydraulic Action -Attrition -Solution-
15Methods of Transportation Rivers transport material in 4 main waysSolution - Some minerals (particularly in limestone areas) dissolve easily in water and are not visible to the naked eyeSuspension – 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.
16Methods of Transportation Saltation - Heavier particles may not be held in the flow all the time but may be bounced along the bedTraction - The heaviest particles are rolled along the bed. Such particles may only be moved when the river has a large volume of water in it
17Methods of Transportation Solution -Suspension-Saltation -Traction -
19River FeaturesRivers 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 and Lower Course at the Mouth of the river. The river displays different characterisitics at each section
20How to take notes on each of the River Features! Course: Upper / Middle / LowerFeature: Eg WaterfallDiagram to illustrate: (make sure that this is labelled!)Notes to explain how the feature happens:Example of this feature:Make sure that you take a new page for each new feature!
37Upper Course Interlocking Spurs Also known as ‘Torrent’ or ‘Youth’ stagesInterlocking SpursIn 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
67..can you mark on this the fastest flow? What is a meander?..can you mark on this the fastest flow?
68… where do you think erosion would take place? What is a meander… where do you think erosion would take place?
69Can you draw a cross section x-y? What is a meander?Can you draw a cross section x-y?
70… this is what a cross section through a meander looks like What is a meander?… this is what a cross section through a meander looks like
71Middle Course Meanders 1 Also known as the ‘Mature’ stage (Aerial View)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
72Middle Course Meanders 2 EROSION TYPE: Lateral (Profile View / Cross Section X - Y)EROSION TYPE: LateralThis 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.
73… this is what a cross section through a meander looks like What is a meander?… this is what a cross section through a meander looks like
83Middle Course Ox-Bow Lake 1 EROSION TYPE: Lateral (Aerial View)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.EROSION TYPE: Lateral
84Ox-Bow Lake 2 (Aerial View) Middle CourseOx-Bow Lake 2 (Aerial View)
87Leveés and Raised Beds 1 (Front View) Lower CourseLeveés and Raised Beds 1 (Front View)DEPOSITION FEATURE: no erosion in the Lower CourseLeveés are formed when rivers flood. The river water overflows the banks of the river and immediately slows down due to friction with the FLOODPLAIN. This drops the larger particles first, building up a raised river bank called a LEVEÉ.
88Leveés and Raised Beds 2 (Front View) Lower CourseLeveés and Raised Beds 2 (Front View)DEPOSITION FEATURE: no erosion in the Lower CourseRaised beds form in the Summer months when the river volume and energy are low and load is dropped onto the river bed. The bed raises up and the capacity of the river reduces, causing flooding in the winter. This in turn builds up the leveés and the whole process raises up the level of the river in the landscape.
89Braided Channels (Oblique Side View) Lower CourseBraided Channels (Oblique Side View)DEPOSITION FEATURE: no erosion in the Lower CourseIn 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.
91Lower Course 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.