Rivers Flashcards
What is the river’s course split into?
Upper course
Middle course
Lower course
As the river moves from its upper course towards its lower course, what happens to the gradient?
The gradient decreases
Explain and describe the river’s upper course
In the upper course, erosion dominates over deposition.
This means that:
The valley is steep-sided and shaped like a V.
The channel that the water flows through is narrow and not very deep
Explain and describe the river’s middle course
In the middle course, neither erosion nor deposition is particularly dominant.
This means that:
The valley has a gentle slope.
The channel is wider than at the upper course. The channel is also deeper than at the upper course
Explain and describe the river’s lower course
In the lower course, deposition dominates over erosion.
This means that:
The valley is wide and flat.
The channel is wide and deep
What are the characteristics of valleys and channels in the upper courses of rivers?
Shallow channel
Narrow channel
V-shaped valley
Steep valley
Where in a river is the gradient the steepest?
Upper course
In the upper course what dominates over deposition?
Erosion
What is the upper course’s channel like?
Narrow and shallow
What is the upper course’s valley like?
Steep - sided and shaped like a V
In the middle course which process is dominant?
Neither erosion nor deposition is particularly dominant
What is the valley like in the middle course?
Has gentle slope
What is the channel like in middle course?
Channel is wider than at the upper course
Channel is also deeper than at the upper course
What process dominates the lower course?
Deposition
What is the valley like in the lower course?
Wide and flat
What is the channel like in the lower course?
Wide and deep
What are the two types of erosion that affect a river’s cross profile?
Vertical erosion and lateral erosion
What is vertical erosion?
Vertical erosion makes the river valley deeper.
Vertical erosion dominates in the upper course.
This is because high levels of turbulence make rough and angular particles drag along the river bed
Why does vertical erosion dominate the upper course?
This is because high levels of turbulence make rough and angular particles drag along the river bed
What is lateral erosion?
Lateral erosion makes the river valley wider.
Lateral erosion dominates in the lower course and middle course
What is abrasion?
where pieces of rock are picked up by the river or sea water and hit against the bed or the banks. This wears them away
What is attrition?
where pieces of bedload (material carried by a river or seawater) are hit against one another. This causes them to break apart and become smaller and more rounded
What is solution?
where soluble rocks are dissolved by the water in the river or sea (limestone and chalk in particular). They are carried along with the river or sea
What is hydraulic action?
where the force of the water hits against the river or sea bed and banks and causes the rock to break off
What are the 4 processes of transportation?
Solution
Suspension
Saltation
Traction
What is suspension?
where silt (sand, clay or other material) and sand particles are held in water (but not dissolved). The silt and sand particles are then transported along with the water
What is saltation?
where small sand and gravel particles bounce along the river bed or sea bed.
They will travel in the direction of the flow of water
What is traction?
where large rocks or large particles are dragged along the river bed or sea bed by the current
Why does deposition of sediment happen?
A river slows down
Reasons why rivers lose velocity and drop material…..?
Increased amount of sediment in the channel
Water becomes shallower
The river’s mouth is reached
Reduced volume of water in the channel
In which part of river’s does deposition not happen?
Upper course
In what part of a river world you find interlocking spurs?
Upper course
What erosional process is predominantly responsible for the formation of plunge pools?
Abrasion
Why are interlocking Spurs in the upper course?
In the upper course, rivers do not have enough energy to erode sideways (lateral erosion). Instead, they follow the winding path through the valley. These interlocking hillsides are the interlocking spurs
Hillsides on either side of a river that interlock are called…..?
Interlocking Spurs
Gorges are formed when……….retreat over time?
Waterfalls
Which processes lead to the formation of meanders?
Erosion
Deposition
How are slip off slopes created?
The current is weakest where the water is shallowest, opposite the river cliff. More sediment is deposited here because the current has less energy to carry it along the river. This creates slip-off slopes
What river landforms are caused by Erosion and Deposition?
Meanders
Ox-Bow lakes
Over time, as Meanders get bigger until what forms?
An ox-bow lake
What is created opposite a river cliff in shallow waters because of deposition?
A slip off slope
What do we call a meander that only has a small bit of land between the bends?
Swan’s neck meander
What leads to the formation of a river cliff?
More erosion happening on the outside of river bends
Why is more sediment deposited at slip-off slopes than river cliffs?
The water is shallower and the current has less energy
What is a flood plain?
the wide area of flat land that surrounds rivers in their lower courses at the bottom of a valley
What do we call the wide valley floors that surround rivers in their lower courses?
Flood plains
What are the effects of meander migration?
Meanders flatten valley floors by migrating downstream
Meanders widen flood plains by migrating across them
How are levees created?
Levees are created naturally during floods.
When a flood happens, water overflows over the banks of a river.
The larger sediments that were being transported by the river will be deposited first.
After lots of floods, levees (which are natural piles of sediment) are created at the side of the river.
What are levees?
Piles of sediment that form at the side of river channels after repeated flooding
What do we call the small rivers found in deltas?
Distributaries
What are deltas?
low-lying bits of land where rivers meet the ocean (or lake)
How do deltas form?
Deltas form because rivers lose momentum in the flatter lower course as they reach the ocean, causing them to deposit their sediment load.
The river’s channel can be blocked by this build-up of material. This splits the river into lots of tiny rivers named distributaries.
If this material builds up enough, a piece of land called a delta is created.
Name 4 reasons which cause a river to slow down and deposit sediment
Water becomes shallower
Decreased volume of water
River reaches its mouth
Increased amount of sediment
Why do deltas form?
because rivers lose momentum in the flatter lower course as they reach the ocean, causing them to deposit their sediment load
What factors affect river landscape and sediment load?
Climate
Slope processes
Geology
How does climate affect river landscape and sediment load?
Heavy rainfall causes high runoff because the water arrives so quickly that there isn't enough time for it to infiltrate the soil. Prolonged rainfall makes the soil become saturated, and so any more rainfall will run off instead of infiltrating. Erosion happens faster when there is higher river discharge. More material (or sediment) is transported when a river has more energy
How do slope processes affect river landscapes and sediment load?
In steeper valleys, more debris is likely to be pulled by gravity down the valley to the river bed.
Mass movement can add a lot to a river’s load. Mass movements are more likely during cold weather or during intense periods of precipitation.
Soil creep is when gravity causes soil to fall down a valley or slope. This can add large amounts of fine material to a river’s sediment load
How does geology affect river landscapes and sediment load?
Soft rock erodes faster than hard rock. Therefore, a river will have a lower sediment load if it flows over hard rock.
In areas of harder more resistant rocks, valleys are usually steeper.
Waterfalls are created where soft and hard rock meet.
Interlocking spurs are created when soft rock erodes more quickly than hard rock (a bit like bays and headlands on coastlines)
When does erosion happen slower?
When rovers flow through areas of hard rock, and so the river will have a reduced sediment load
What results in a larger sediment load?
Softer rock
Wetter climate
Steeper slopes
What is river discharge?
the volume of water flowing in a river every second and is measured in cumecs
What are the physical factors affecting storm hydrographs?
Geology Soil type Slope Drainage basin type If the ground has been frozen
What is river discharge measured in?
Cubic meters per second
What factors affect the risk of flooding?
Geology
Relief
Land use
Precipitation and storms
How is high discharge likely to increase erosion?
Increased discharge increases the velocity of the water flowing so hydraulic action and abrasion would be most effective
What is a confluence?
The point where two rivers merge
This can happen at any stage of the river
What is a tributary?
A smaller river that feeds into another river
How are meanders formed?
Continued erosion can create a narrow neck between two meanders
Eventually the neck will be breached out, cutting off the meander to create an oxbow lake
What are the three main ways water can reach a river?
Precipitation
Surface run off
Through flow
How are deltas formed?
When the river deposits its material faster than the sea can remove it
Name the types of deltas
Fan shaped
Cuspate
Bird’s foot
What is a fan-shaped delta?
the land around the river mouth arches out into the sea and the river splits many times on the way to the sea, creating a fan effect
What is a cuspate delta?
the land around the mouth of the river juts out arrow-like into the sea
What is a bird’s foot delta?
the river splits on the way to the sea, each part of the river juts out into the sea, rather like a bird’s foot
Name one way human activity can affect hydrographs
Increased urbanisation which increases the surface run off. This reduces infiltration so flooding increases
Explain one way rivers transport their load
Traction - this involves the sediments being rolled along the river bed.
Explain two differences between the upper course and lower course river landscapes
Upper course landscapes have a narrower river channel due to vertical erosion eroding downwards rather than laterally
The lower course has deltas due to a gentle gradient and deposition
Name land forms created in the upper course
V shaped valleys, interlocking Spurs and waterfalls
This is caused by steep gradient and vertical erosion
Name land forms created in the middle course
Flood plains, meanders and oxbow lakes
This is due to gentler gradient and lateral erosion
Name land forms created in the lower course
Flood plains, deltas and levees
This is due to a gentle gradient and deposition
How does a steeper valley affect a hydrograph?
A steeper valley will funnel more rainfall into a river faster, increasing river discharge.
How do impermeable rocks affect a hydrograph?
Impermeable rocks will absorb less water and channel more rain into a river, increasing discharge (infiltration is lower)
How do impermeable soils affect a hydrograph?
Impermeable soils will have higher runoff and channel more water into a river
How do circle drainage basins affect a hydrograph?
Circle-shaped drainage basins will channel more water into a river, reducing the lag time
How does weather affect a hydrograph?
If the weather has been cold and the ground is frozen, the runoff will be higher, decreasing the lag time on the hydrograph
How does deforestation affect a hydrograph?
Deforestation means that less water will be intercepted by trees, reducing the lag time from rainfall to peak discharge
How do impermeable buildings affect a hydrograph?
Impermeable building materials are used for housing and buildings in urban areas. This will reduce infiltration and reduce the lag time
How does geology affect river flooding?
Runoff is higher in areas that are mainly made up of impermeable soil (e.g. clay) or impermeable rock (e.g. granite)
How does precipitation and storms affect river flooding?
Heavy rainfall causes high runoff because the water arrives so quickly that there isn’t enough time for it to infiltrate the soil.
Prolonged rainfall makes the soil become saturated, and so any more rainfall will run off instead of infiltrating.
If storms are more frequent have more rainfall, then the risk of flooding will rise
How does land use affect river flooding?
Buildings and roads are usually made of impermeable materials. More impermeable surfaces mean more runoff and more discharge.
Trees intercept water and store water that they take up from the ground. Removing trees will, therefore, increase flooding risk as more water will be finding its way into the river channel
How does relief affect river flooding?
Rainfall will reach the river channel quicker in a steep-sided valley
What threats are posed to the environment by the flooding of rivers?
Contaminated floodwater can pollute river habitats
Deposited silt and sediment can damage agricultural land
Erosion of river banks can significantly change the landscape of a river
Vegetation can be uprooted by forceful floodwater
Explain why the antecedent conditions in a drainage basin can affect the peak discharge of a river’s hydrograph
If there has been a lot of rain the ground will be saturated and cannot take any more
Therefore more water runs off the surfaces thus reaches the river in shorter time, hence higher peak discharge
