Rivers (Yr 11)

Question 1

What’s a river/drainage basin?

Answer 1

An area of land drained by a river and it’s tributaries.

Question 2

What’s a watershed?

Answer 2

The boundary / highest points surround a drainage basin. Everything within the watershed (within a boundary) would be part of the same drainage basin.

Question 3

What’s a source?

Answer 3

The point where the river begins.

Question 4

What’s a tributary?

Answer 4

A small stream or river which flows into the main river.

Question 5

What’s a confluence?

Answer 5

Where a tributary joins the main river.

Question 6

What’s the mouth?

Answer 6

The end of a river

Question 7

What does a river long profile look like?

Answer 7

It’s a side view and looks like a graph which rapidly decreases then flattens out towards the end.

Question 8

What’s a river cross profile?

Answer 8

It’s like taking a cut of the river.

At point A - the river source, the river sides are high and steep and the river is narrow

Point B is the middle

At point C - the river mouth, the sides aren’t steep, almost the same hight as the river, and the river is quite wide.

Question 9

What’s evaporation?

Answer 9

Water turning into water vapour

Question 10

What’s evapotranspiration?

Answer 10

The sum of evaporation from the Earths surface with the transpiration of plants.

Question 11

What’s groundwater flow?

Answer 11

Sideways movement of water underground through rocks

Question 12

What’s infiltration?

Answer 12

Seeping of water downwards into the soil

Question 13

What’s interception?

Answer 13

Collection of water by vegetation

Question 14

What’s precipitation?

Answer 14

Any form of moisture that falls from the atmosphere

Question 15

What’s surface run-off?

Answer 15

All water flowing on the Earth’s surface

Question 16

What does sustainable mean?

Answer 16

Capable of existing in the long term

Question 17

What’s through flow?

Answer 17

Sideways movement of water through soil

Question 18

What’s transpiration?

Answer 18

Loss of moisture from plants

Question 19

What’s percolation?

Answer 19

The downward movement of water through soil and rock

Question 20

What’s the water table?

Answer 20

The upper level of underground water.

Question 21

What’s the hydrological cycle?

Answer 21

The movement of water around the earth in a cycle through land, sea and the atmosphere. It changes state (sold, liquid and gas) but there’s no ‘new’ water and no water disappears - it’s a closed system.

An open system would be one where ‘new’ water is added or taken away and water can be lost altogether. The total amount of water varies.

Question 22

What’s weathering?

Answer 22

When nature breaks down rocks in situ (there is no movement, it happens in one place).

Question 23

What’s erosion?

Answer 23

When a moving force (e.g. water) wears away parts of rock and removes weathered material.

Question 24

What are the types of weathering?

Answer 24

Chemical
Biological
Physical

Question 25

What’s biological weathering?

Answer 25

When plants and animals break up rocks.
Plants grow in cracks in the rocks and their roots push the rocks apart.
Animals burrow and break up the rocks.

Question 26

What’s chemical weathering?

Answer 26

Weakening of rock by chemicals e.g. Rain is slightly acidic so, when it comes in contact with rock, it wears away the top layer of the rock.

Question 27

What’s physical weathering e.g. Freeze thaw

Answer 27

Weathering due to physical/direct changes
E.g. Freeze thaw is when, in upland areas where it gets cold, water gets into cracks in the rocks and freezes.
The water expands when it turns to ice so it puts pressure on the rock which causes the rock to break up.

Question 28

What’s abrasion / corrasion?

Answer 28

When sand and pebbles get dragged along the river bed or knock into it as they bounce along the water, wearing away at the channel.

Question 29

What’s hydraulic action?

Answer 29

Fast-flowing water pushes air into cracks and the sheer force if this breaks up the channel over time.

Question 30

What’s attrition?

Answer 30

When rocks and stones moving in the water knock together and help to wear each other away.

Question 31

What’s solution/corrosion?

Answer 31

When water dissolves minerals from the river bed and banks and this helps break up the channel.

River water dissolves some types of rock e.g. Chalk and limestone

Question 32

What does the rate of erosion depend on?

Answer 32

Human activity
Gradients of the river basin
Rock type
Load (material being transported)

Question 33

How does human activity affect the rate of erosion?

Answer 33

E.g. Deforestation
Removing trees helps speed up erosion as it allows rainfall to run over the soil, washing it into rivers. This clogs up the river. Stones and other materials contribute to attrition.

Question 34

How does the gradients of the river basin affect the rate of erosion?

Answer 34

The steeper the landscape, the faster the river flows (and with more energy).

Question 35

How does the rock type affect the rate if erosion?

Answer 35

Different rock types erode at different speeds. Soft rock like sand will erode quickly; hard rock e.g. Granite takes longer.

Question 36

How does the load affect the rate of erosion?

Answer 36

More materials means more rocks and pebbles to help erode.

Question 37

What’s vertical erosion?

Answer 37

This occurs in the upper course of the river where gravity encourages the river’s energy to erode downwards.

Question 38

What’s lateral erosion?

Answer 38

This occurs in lower sections of the river as the valley is less steep so energy is used to erode sideways.

Question 39

What’s channel storage?

Answer 39

When water is held in a river.

Question 40

What happens in the hydrological cycle?

Answer 40

1) Evapotranspiration occurs from evaporation from the sea and land and transpiration from plants.
2) Water vapour is moved inland by winds
3) The water vapour condenses to form clouds and then falls over land as precipitation

4) Water flows or is transferred by:
Infiltration - when water soaks into the soil
Percolation - when water moves down through rock and soil
Through flow - water in soil flows downhill
Groundwater flow - water in rock flows downhill
Surface runoff - when water flows overground
Channel flow - flow of water in a river

5) Water can be stored on the land as:
Channel storage - held in a river
Groundwater storage
Interception storage
Surface storage 

6) Eventually the water ends up in the sea and the cycle repeats

Question 41

What’s a drainage basin?

Answer 41

The area of land drained by a river.

Question 42

What’s the course of a river?

Answer 42

The path of a river as it flows downhill.

Rivers have an upper, middle and lower course

Question 43

What’s a river long and cross profile?

Answer 43

Long: shows how the gradient of the river changed over the different courses of the river

Cross: shows what a cross section of the river would look like

Question 44

What’s transportation and what are the 4 methods of transportation?

Answer 44

The movement of eroded material.

Traction
Saltation
Suspension
Solution

Question 45

What’s deposition?

Answer 45

When a river drops eroded material.

It happens when a river slows and loses velocity

This may be because:
The volume of water in the river falls
The load in the water increases
The water is shallower e.g. The inside of a bend
The river reaches it's mouth

Question 46

Where do waterfalls and gorges form?

Answer 46

In the upper course of a river

Question 47

How are waterfalls and gorges formed?

Answer 47

Waterfalls form where a river flows over an area of hard rock followed by an area of soft rock.

The softer rock is eroded more than the hard rock creating a step in the river.

As water goes over the step it erodes more and more of the softer rock.

A steep drop is eventually created which is called a waterfall.

The hard rock is eventually undercut by erosion which becomes unsupported and collapses.

The collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rock by corrasion, creating a deep plunge pool.

Over time, more undercutting causes more collapses. The waterfall will retreat leaving behind a steep sided gorge

Question 48

What are interlocking spurs?

Answer 48

In the upper course of a river most of the erosion is vertically downwards. This creates steep sided V shaped valleys.

The rivers aren’t powerful enough to erode laterally - they have to wind around the high hillsides that stick out into their paths on either side.

The hillsides that interlock with each other (like a zip from birds eye view) as the river winds around them are called interlocking spurs.

Question 49

What are meanders?

Answer 49

Found in the middle and lower courses of the river.

The current is faster on the outside of the bend because the river channel is deeper.

More erosion takes place on the outside of the bend, forming river cliffs.

The current is slower on the inside of the bend because the river channel is shallower.

Eroded material is deposited on the inside of the bend forming slip off slopes.

Question 50

How do you oxbow lakes form?

Answer 50

Meanders get larger over time and eventually turn into an oxbow lake.

Erosion causes the outside bends to get closer until there is only a small bit of land is left between the bends called the neck.

The river breaks through this land usually during a flood in the river flows along the shortest course.

D position eventually cuts of the meander forming an oxbow lake.

Question 51

What are floodplains?

Answer 51

Wide valley floor is on either side of the river which occasionally get flooded

When a river floods onto the floodplain the water slows down and deposit the eroded material that it is transporting which builds up the floodplain

Meanders migrate across the floodplain making it wider

Do you position that happens on the slip off slopes of meanders also builds up the floodplain

Question 52

What are levees?

Answer 52

Natural embankments (raised bits) along the edges of a river channel. 
These build up after repeated flooding.

Question 53

What are deltas?

What are the types of delta?

Answer 53

Low lying areas where a river meets the sea or a lake.

Arcuate - have a rounded shape and lots of distributaries

Cuspate - have a triangular shape and few distributaries

Birds foot - shaped like a birds foot

Question 54

What is river discharge and what factors affect it?

Answer 54

The volume of water flowing in a river per second.

Factors increasing discharge:
High / intense rainfall - more runoff - shorter leg time
Impermeable rock - can’t infiltrate into the rock - more runoff
Steep slopes - more runoff
Less vegetation - less water intercepted

Factors decreasing discharge:
Low / light runoff - less runoff - longer lag time
Permeable rock - water can infiltrate the rock
Gentle slopes - less runoff
More vegetation - more water interception

Question 55

What are the causes of flooding?

Answer 55

Prolonged rainfall
Snowmelt
Heavy rainfall
Geology
Relief (height of the land)
Deforestation
Urbanisation

They can kill people, damage buildings and jobs are lost

Question 56

What are the methods of hard and soft engineering to reduce the risk of flooding?

Answer 56

Dams and reservoirs (high built walls and artificial lakes)

Channel straightening (straightens the river’s course and meanders are cut out)

Man made levees (Man made embankments)

Flood warnings

Preparation

Floodplain zoning and restricting building on parts of the floodplain