River Changes And LandformsPresentation Transcript
River Characteristics, Changes & Landforms
Catchment The area from which water drains into a particular drainage basin. Tributary A river which joins a larger river. Confluence The point at which two rivers join. Watershed The boundary dividing one drainage basin from another- a ridge of high land. What is a drainage basin? Source The upland area where the river begins. Mouth Where the river flows into the sea, or sometimes a lake.
Watershed Tributary Features of a drainage basin on a map. Confluence a b c Source d
The Long Profile of a River Changes in the river as it goes downstream from source to mouth.
Long Profile Height above sea level in meters . 0 50 100 150 200 250 A Upper Course B Middle Course C Lower Course
30 25 20 15 10 5 0
Distance from sea in Kms.
Gradient/slope decreasing Velocity/flow increasing Cumecs/discharge increasing Energy increases
Valley & Channel Cross-Sections A Upper Course B Middle Course C Lower Course
What are the main features of a river? The fastest section of the river, as the channel is widest, with very smooth sides, and the greatest volume of water. The water has increased in speed as the channel widens and becomes smoother. Some boulders cause friction to slow it down a little. Relatively slow moving. Despite areas of fast flowing water, the large amount of material on the river channel bed means that friction will slow the water down. Velocity Deltas; flood plains; levees; meanders; ox-bow lakes Meanders; slip-off slopes; ox-bow lakes Interlocking spurs; waterfalls; V-shaped valley; gorges Features Mainly suspension and solution. Saltation, suspension and solution Traction and saltation Transportation Primarily cuts laterally as it has almost reached base level. The erosive energy of the river is almost totally concentrated on cutting sideways. Much deposition occurs. Continues to cut vertically. But it also begins to cut laterally as it gets closer to base level. Deposition occurs in the slower moving insides of meanders. Primarily vertical erosion, through attrition, abrasion and hydraulic action. Large boulders deposited and eroded in situ. Erosion & Deposition Wide, shallow valley, with large flood plains and meanders. The river channel is wide, deep and smooth sided. v-shaped valley remains with a wider valley floor and the river begins to meander across it. The river channel begins to widen and become deeper. Steep sided v-shaped valley. Thin river channel, deep in places Cross Profile Almost at sea level, very gently sloping towards its mouth Shallow slopes towards the mouth of the river Steeply sloping towards the lower sections of the river Long Profile Lower Course Middle Course Upper Course
The Upper Course of a river
To know and understand the formation of landforms in a river’s upper course.
To understand the processes that operate in a river’s upper course
What processes occur in a river? There are 3 processes taking place in every river. These are: Erosion Transportation Deposition (The wearing away of the land) (The movement of eroded material) (The laying down of eroded material) There are also two other processes that shape the river valley. These are weathering and mass movement.
Shaping the river valley.
There are also two other processes that shape the river valley. These are weathering and mass movement .
Weathering = the breakdown of rock material.
Mass movement = the movement downslope of broken down rock material due to gravity.
Weathering & Mass Movement. The 3 main types of weathering are show below in the wrong order. Sort the statements out into the right order and copy these onto your sheet. Underneath copy out a definition of mass movement.
Erosion Processes Match up the key word with the definition.
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.
Erosion Processes Match up the key word with the definition. Abrasion (Corrasion) is when the river is loaded with material in suspension and scours away at the river banks. (Sandpaper effect) Hydraulic Action is the shear force of the river impacting on the sides of the river banks. Corrosion is substances carried in solution such as acids. They dissolve rocks away over long periods of time. Attrition is when bed load collides into each other with the current flow and breaks down into smaller particles.
Key words - Transportation.
Traction – where large rocks and boulders are rolled along the river bed. Happens most in times of flood, when the current is strongest.
Saltation – where smaller stones are bounced along the river bed in a leap frogging motion
Suspension – where very small grains of sand or silt are carried along with the water
Solution – where some material is dissolved (like sugar in a cup of tea) and is carried downstream. Occurs often in limestone landscapes where the water if very acidic.
Methods of transportation. Traction Saltation Suspension Solution Shows the rate of flow needed
Upper valley characteristics
Upper valley characteristics Can you add an annotation to each arrow to explain the characteristic?
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
Narrow Channel Lots of tributaries High land so source of river Contour lines close together – steep valley sides Steep river gradient – contours close together Direction of flow shown by lower land No flood plain and V-shaped valley
1 2 3 4
Interlocking spurs A typical upper course V-Shaped valley with interlocking spurs , steep valley sides and active slope processes. The diagram below shows the formation of interlocking spurs.
Can you draw an annotated sketch of this valley to show how it is formed?
River load in upper course Boulders are large and semi-rounded, due to attrition within the load and abrasion with the stream bed and banks Why are they rounded?
Rapids in the Upper Tees Valley
Formation of Rapids
High Force waterfall, R. Tees WHAT IS A WATERFALL? A waterfall is formed where water flows over a cliff or very steep drop in the river's bed.
High Force Waterfall R. Tees
Formation of a Waterfall.
A waterfall is a steep drop in the course of a river.
They form when a band of hard resistant rock (cap rock) lies over softer, less resistant rock.
The softer rock is quickly eroded by hydraulic action and abrasion, causing the harder rock to be undercut.
The hard rock overhangs until it can no longer carry its own weight.
The overhang collapses and then breaks up in the water below.
The great power of the water at the base of the waterfall causes a plunge pool to form.
The bed of the river below the waterfall contains boulders eroded by splash back from behind the waterfall.
Over time the process above is frequently repeated and eventually a steep-sided gorge forms as the waterfall retreats up stream.
Waterfall formation Look at the diagram, How is a waterfall formed ?
Can you put the labels below into the correct place on he diagram?
High Force waterfall, R. Tees Waterfalls create a gorge upstream as they recede, This is a steep sided valley with no floodplain.
Upper Course of a River Land use: Few settlements, Recreation, Farming, Forestry Steep valley sides Evidence of tributaries Reservoir High land Narrow channel and no floodplain
The Middle and Lower Course of a River
To understand the main processes that operate in the middle and lower course of a river.
To understand how meanders and oxbow lakes are formed.
This is a picture of a river in its middle course. Can you recognise and explain the differences between the upper and middle course of a river?
Erosion is still an important process. The river is now flowing over flatter land and so the dominant direction of erosion is lateral (from side to side). The river has a greater discharge and so has more energy to transport material. Material that is transported by a river is called its load . Deposition is also an important process and occurs when the velocity of the river decreases or if the discharge falls due to a dry spell of weather. Processes operating in the middle course of a river
DEPOSITION and EROSION create these landforms What landforms are found in the middle course?
A meander = a bend in a river Can you match up the characteristics below? There is little frictional drag from the bed and bank at this point and so the river can flow at this speed. Slowest flow Maximum depth of the channel. (Note the asymmetrical cross-profile) Fastest flow Because of the gentle slope, there is a lot of frictional drag and so therefore the river flows at this speed River cliff Formed on the outside bend of the meander due to erosion. Slip off slope A gently sloping area of land on the inside of a meander Deep water
Meanders 1 2 3
Floodplain Deposits on the inner meander bend where there is low energy Erosion on the outer bend where there is faster flow. It creates a river cliff Slip-Off Slope Direction of meander migration
Can you match up the labels to the correct place on the diagram?
Cross section through a meander
Ox Bow Lake Formation Can you look at the diagram & explain the formation of ox-bow lakes?
Ox Bow lake on Mississippi
More gentle sloping valley sides Evidence of meanders Land use changes – more urban areas. Small floodplain begins to develop on either side of the river,
The Lower Course of a River Learning Objectives: To be able to describe and explain the formation of a flood plain, levees, delta and estuary.
Floodplains, Deltas and Levees.
The pictures below show a floodplain, a delta and levees. Using your prior knowledge of river processes come up with a theory to explain how they are formed. The key words underneath each picture will help.
deposition Slow flow alluvium (silt) flood flat deposition slow sea/lake load channel blocked deposit flood large load smaller load Main Channel Main Channel Levee Sea/lake Floodplain Floodplain
A flood plain is the wide, flat area of land on either side of the river in its middle and lower course.
Levees are natural embankments of silt along the banks of a river, which are often several metres higher than the flood plain.
Floodplains and leve é s are formed by deposition in times of river flood.
The river’s load is composed of different sized particles.
When a river floods, t he river water overflows the banks of the river and immediately slows down due to friction.
This drops the larger particles first, building up a raised river bank called a LEVEÉ.
The sands, silts and clays are similarly sorted with the sands being deposited next, then the silts and finally the lightest clays. This builds up the floodplain.
Floodplain & Levee formation
This is a cross section of a floodplain. Can you draw a simple sketch of the diagram and the labels below and then annotate it to explain how it is formed? How a floodplain is formed leve é s clays and silts sands
Delta Formation Deltas form at the mouths of many of the world’s larger rivers, e.g the Nile (Egypt), the Ganges (Bangladesh), the Mississippi (USA).
A delta is a flat area of sand and silt built into the sea. It is formed by deposition.
When a river enters a sea or lake carrying large volumes of fine material, the velocity slows and causes the load to be deposited in layers.
Over time, the deposited material blocks channels and forms small islands separated by river channels called distributaries.
Estuaries There are no large deltas around the coasts of the UK, instead the tidal mouth of a UK river is typically characterised with an estuary. Estuaries are wide river valleys flooded daily by the tide. At low tide, large expanses of mud and sandflats are exposed which are mostly composed of material deposited by the river, e.g Thames, Humber, Severn. Thames Estuary