Rivers

Question 1

abrasion (corrasion)

Answer 1

When rocks and silt carried along by the river wear down the river bed and bank

Question 2

hydraulic action

Answer 2

When the motion of water against the rock produces gradual mechanical weathering of the river bed and banks

Question 3

attrition

Answer 3

When rocks which are transported by the river smash together and break into smaller, smoother and rounder particles

Question 4

solution (corrosion)

Answer 4

When small, soluble particles are dissolved into the river

Question 5

traction

Answer 5

When the force of the water rolls large boulders along the riverbed (a river usually only has this much force in times of flooding)

Question 6

saltation

Answer 6

When small pebbles and stones bounce along the riverbed as the river picks them up then drops them as they are too heavy to keep afloat

Question 7

suspension

Answer 7

When fine light material (which can be kept afloat) is carried along with the water

Question 8

solution

Answer 8

When minerals are dissolved in the water and carried along in solution (eg. salts)

Question 9

pot holes & eddy currents

Answer 9

Boulders broken off by erosion sit on the river bed creating eddy currents as the water flows past since the river current is too weak to move the boulders by traction. The boulders swirl by the eddy currents, grinding a hole into the riverbed by abrasion.

Question 10

alluvium

Answer 10

Alluvium is an extremely fertile soil that is very use full for planting crops, and in general farming. The alluvium is created from the river’s silt when it is piled layer upon layer during floods. This takes thousands of floods depositing the silt.

Question 11

Angel Falls

Answer 11

Venezuela, 979 meters (19 times the height of the Niagara Falls!), highest waterfall in the world, source: upper tributary of Rio Caroni

Question 12

aquifer

Answer 12

An underground layer of permeable rock, sediment or soil that provides water. The best aquifers are sandstones, unconsolidated gravels and permeable limestones. They can be a few square kilometers to thousands of square kilometers in size.

Question 13

braiding

Answer 13

Braided channels are features that occur in the lower course of a river. The braids in the channel occur because of piles of sediment deposit that block the river from going in its natural course (shallow water). Therefore, because water chooses the path of least resistance, it goes around the pile of sediment and then rejoins the channel, thus the braiding. This forms islands in the river called eyots.

Question 14

condensation nuclei

Answer 14

When tiny particles invisible to the human eye such as dust and dirt provide surfaces on which water molecules can condense and gather into water droplets.

Question 15

condensation

Answer 15

The process by which water vapor in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds. These clouds may produce precipitation, which is the primary route for water to return to the Earth’s surface within the water cycle. Condensation is the opposite of evaporation.

Question 16

confluence

Answer 16

Where a smaller stream or river meets and joins a larger river.

Question 17

Dams and reservoirs

Answer 17

A dam is any barrier that holds back water; dams are primarily used to save, manage, and/or prevent the flow of excess water into specific regions. In addition, some dams are used to generate hydropower. A reservoir is a man-made lake that is primarily used for storing water. They can also be defined as the specific bodies of water formed by the construction of a dam.

Question 18

Deforestation

Answer 18

Deforestation is a term used to describe the removal of trees for many uses such as wood or open space for example. Deforestation can cause a very big problem when it comes to flooding. This is because if you don’t have trees, it is very hard for the water to be absorbed because there is nothing to absorb it. When there is no trees and a flood is present, the ground just has a lot of surface run-off.

Question 19

Deltas

Answer 19

A land form at the mouth of a river, where the river flows into an ocean, sea or lake. Deltas are formed from the deposition of sediment carried by the river as it leaves the mouth of the river.

Question 20

Deposition

Answer 20

Deposition is when a river that is containing things such as; rocks, sand, mud, etc drops the things it is carrying, when the speed of the river slows down, or if the volume of the river decreases. Deposition majorly occurs in floods, which then makes the land after the flood better for farming because the land is more fertile. The heavier objects deposit from the river first, and then the smaller object deposit after.

Question 21

Dew point

Answer 21

The temperature at which water vapour in a specific volume of humid air condenses into liquid water, forming in this case precipitation such as rain and, after more cooling, snow.

Question 22

Discharge

Answer 22

Discharge is the volume of water to flow at a give point on a stream bank per unit of time. It is usually expressed in cubic meters of water per second (m3/s). This is the volume rate of water flow which could include things such as dissolved chemical species, biological material and suspended solids (such as sediment). It is calculated by the equation: area of river cross section (calculated by adding up area of subsections (depth * width)) multiplied by the velocity

Question 23

distributary

Answer 23

A branch of river that flow off from the main channel and does not rejoin it.

Question 24

drainage basin

Answer 24

The area of land drained by a river.

Question 25

dredging

Answer 25

When sand and gravel is removed from the coastline or seabed. It is a type of flood management, because now more water can go into the river, lake or sea because there is a smaller seabed.

Question 26

evaporation

Answer 26

The change of state from water as a liquid into water vapour (a gas)

Question 27

flood plain

Answer 27

The area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich alluvium deposited by floodwaters. This makes floodplains a good place for agriculture.

Question 28

flood relief channels

Answer 28

A channel which redirects water away from the river during a flood to avoid there having civilian problems.

Question 29

gorge

Answer 29

A narrow valley, with steep rocky walls, typically created by a waterfall receding back upstream when the soft rock is eroded, and carving deeper into the ridge above it.

Question 30

groundwater flow

Answer 30

The sideways movement of water through the bedrock, which is typically an aquifer

Question 31

through flow

Answer 31

The horizontal movement of water through the soil zone.

Question 32

hydrological cycle

Answer 32

The process by which water moves through the landscape

Question 33

impermeable rock

Answer 33

If river is in an area of impermeable rock, water can’t percolate into rocks so flows as surface runoff, increases discharge rapidly

Question 34

infiltration

Answer 34

The movement of water into the soil layers

Question 35

interception

Answer 35

Trees and other vegetation, which prevent moisture from reaching the ground directly

Question 36

interlocking spurs

Answer 36

Water will always erode downwards and it will find the easiest way to get where it needs to go. This is how interlocking spurs are formed. The spurs themselves are the more resistant rock, so the water will erode around them into the softer rock creating winding passage ways called interlocking spurs. This feature is normally found in a V-shape valley.

Question 37

land use planning

Answer 37

When you map out the flood plain. You then build cities further away from the river so that if a flood were to occur, then it wouldn’t do much damage. You would then put the farming fields up close to the river so that the land would pretty much always be fertile for growing crops. This concept is when you have a plan before you build so that you avoid more consequences than you would do if you didn’t plan out the region.

Question 38

long profile

Answer 38

A diagram depicting the river in 3 stages: Upper course, middle course and lower course.

Question 39

meander neck

Answer 39

The narrowest part of the river beach. It is the part that gets cut off to then form an oxbow lake.

Question 40

meander scar

Answer 40

Portions of the river that have been abandoned when the meander was cut off. Sometimes the cut-off portion may be filled with water creating an oxbow lake but when the water empties a meander scar is formed.

Question 41

meander

Answer 41

As the river erodes laterally, to the right side then the left side, over flatter land, it forms large bends, and then horseshoe-like loops called meanders. Meanders constantly change their shape and position. When a river reaches a meander, most water is directed towards the outside of the bend. This reduces friction and increases the velocity of the river at this point. The river therefore has more energy to transport material in suspension. This material will erode the outside bank by abrasion (corrasion). The bank will be undercut, collapse and retreat to leave a small river cliff. (This is lateral erosion)

Question 42

Mississippi delta

Answer 42

an example of 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.

Question 43

mouth

Answer 43

When the river meets the sea or ocean it flows into. this often is in the form of a delta or a small pool which is full of a mixture of fresh and salty water.

Question 44

natural levée

Answer 44

Thickest and coarsest sediments are deposited on the channel edges whilst fine, thin sediments are deposited over the outer parts of the floodplain. Natural levées build up by many floods.

Question 45

Niagara Falls

Answer 45

The falls that form the international border between the Canadian province of Ontario and the US state of New York. These falls include the American, the Bridal Veil and the Horseshoe falls. They are located on the Niagara river and have a total height of 51 metres. Out of any waterfall in the world, the Niagara Falls form the highest flow rate. Its average flow rate is of 1,834 m3/s.

Question 46

Nile delta

Answer 46

The Nile delta is formed in Northern Egypt, where the river drains into the Mediterranean Sea. It divides into two main distributaries: the Rosetta and the Damietta. The delta’s outer edges are eroding, and the condition of the soils of the floodplains is decreasing due to the usage of fertilizers and the lack of nutrients that are usually deposited from upstream (this is because of the Aswan High Dam). The Nile delta is one of the longest in the world at 160km in length and covering 240km of the coastline.

Question 47

overland flow

Answer 47

Movement of water over the ground surface (also known as surface run-off)

Question 48

oxbow lake

Answer 48

Occurs when a meander neck completely closes in on itself. Since water chooses the path of least resistance, the water starts only flowing through the straight part of the river, not around the meander. Therefore, eventually, the meander dries up and the part that is completely cut off is then considered an oxbow lake.

Question 49

path of least resistance

Answer 49

Water follows the path of least resistance. For example when a river is young, before time has allowed the undercutting of rock, a river will curve around any hard rocks, simply following the lowest and simplest path between interlocking spurs. This allows the water to flow downhill at a faster speed with the least amount of effort spent.

Question 50

percolation

Answer 50

Downward movement of water into the rock layer

Question 51

precipitation

Answer 51

The product of condensation of atmospheric water vapour which falls due to the gravitational pull of the earth. There are many forms of precipitation, the main ones are: snow, rain, hail, sleet, drizzle, etc.

Question 52

plunge pool

Answer 52

The area where the waterfall drops into. Fallen rocks build up here. Deep due to erosion from water and rocks.

Question 53

rapids

Answer 53

Rapids occur in a fast flowing area of a river where there are many rocks scattered around. If there were no rocks scattered around, then there would not be any rapids, because rapids are formed when they hit rocks and the water has to change path to avoid the rock. Rocks are here, because of deposition and erosion. Deposition because the water can carry rocks and then drop them off into the river bed. Erosion, because the river bed is always being eroded, and the mud is easier to erode than the rocks, therefore leaving big chunks of rocks in river beds.

Question 54

recreating wetlands

Answer 54

The recreation of wetlands is seen in projects all over the world. Most happens in the USA, where wetlands and swamps are frequently built on. This destroys natural habitats for many animals. Recreating wetlands also helps reduce flooding, as the marshland areas can absorb water, preventing the spread of the flooding.

Question 55

river beach

Answer 55

In meanders, the fastest flow is called the thalweg. This creates erosion on the outside of the bend and deposition on the inside of the bend. So, a river beach is an area of deposition that is found on the inside of a meander.

Question 56

river cliff

Answer 56

Water moving in the channel of a river moves in a spiral pattern and the water on the outside of the bend tends to move faster than the rest. This results in erosion of the outer bank and forms a river cliff or an overhang to the river.

Question 57

saturated soils

Answer 57

The ground is too full of water so it can’t absorb any more. This excess will run on the surface of the ground

Question 58

slip off slope

Answer 58

The inside part of the meander bend, where deposits build up. Slope as there is no erosion.

Question 59

source

Answer 59

The beginning or start of a river. Start of the furthest tributary.

Question 60

spring

Answer 60

A point where water flows to the surface from underground. This point is normally in the mountains or on hills and it is usually the start of a river.

Question 61

spring thaw

Answer 61

This is when during the spring there is an overflow of streams and flooding due to compacted snow melting. Neither melted snow nor rainwater can seep into the ground because the land is frozen.

Question 62

steep slopes and flooding

Answer 62

A steep slope has an impact on flooding. For example if it’s been raining for a while, unlike flat and gentle slopes, which allow the water to penetrate into its soil because the water has more time, steep slopes don’t give the water enough time to penetrate into the soil so more water will come down then if it were on a gentle slope. Steep slopes create a fast surface run-off.

Question 63

thalweg

Answer 63

The fastest flow of water in a river. This is why most erosion occurs where the thalweg flows (see the creation of meanders). The thalweg is also indicates the deepest part of the river channel.

Question 64

transportation

Answer 64

This is the process when eroded material such as rocks and gravel are picked up and transported by the river and then they are deposited somewhere else lower down in the river system.

Question 65

transpiration

Answer 65

The movement of water through plant cells into the atmosphere

Question 66

tributary

Answer 66

A stream or smaller river which joins a larger stream or river.

Question 67

v-shaped valley

Answer 67

Formed by the water. This is because, in a river, the area where the current is fastest is in the middle. This is then the area where most erosion occurs. Then, as more erosion occurs, the river goes down leaving above it a V-shaped valley. Many ski resorts are located in V-Shaped Valleys, and a long time ago, in those areas was just a river and no visible land.

Question 68

water table

Answer 68

The level under which rock underground is saturated. This is the level that wells are dug down to, to allow fresh water to be brought to the surface. The level of the water table can change depending on the seasons.

Question 69

waterfall

Answer 69

When a river runs over alternating layers of hard and soft rock, waterfalls may form. Splash back erodes away softer rock under hard rock, hard rock is left overhanging, and because it isn’t supported, it eventually collapses, fallen rocks crash into the plunge pool and swirl around causing more erosion, overtime, this process is repeated and the waterfall moves upstream creating a steep-sided gorge.

Question 70

watershed

Answer 70

Where all the channels and different distributaries of water that are joined flow into the same basin.

Question 71

stem flow/drip

Answer 71

Movement of water from vegetation to the ground surface

Question 72

Evapotranspiration

Answer 72

The combined process by which water is lost by evaporation and transpiration

Question 73

wetted perimeter

Answer 73

Where the water comes into contact with the river’s banks and bed

Question 74

percentage of fresh water in the world and how fresh water is distributed in the world (include % for this too)

Answer 74

3% of the water in the world is fresh, and out of the 3%, 79% is ice caps and glaciers, 20% is groundwater and 1% is accessible surface freshwater

Question 75

Where is the fastest flowing part of the river?

Answer 75

In the lower course

Question 76

List the 4 types of transportation in rivers (you are free to think of the explanation of each in your head too)

Answer 76

traction, saltation, suspension and solution

Question 77

List the 4 types of erosion in rivers (you are free to think of the explanation of each in your head too)

Answer 77

hydraulic action, attrition, abrasion (corrasion), solution (corrosion)

Question 78

Explain the formation of oxbow lakes

remember - for this question on a test, don’t forget to include diagramS

Answer 78

As a meander is formed, gradually, over some time, the outer bends will start to erode away and as they do, the meander neck gets narrower and narrower. Eventually, the river will cut through the thin neck as it seeks the path of least resistance. Now that the river has found a quicker and easier route, it will discontinue going around the entire bend of the meander which got cut through. This means that as the river’s thalweg is now in the middle of the straight path outside of the bend, it will erode here whilst depositing load on the edges. Gradually, this process eventually seals off the old meander to a point where the meander is completely cut off from the river, forming an oxbow lake.

Question 79

How are deltas formed?

Answer 79

As large rivers approach the sea, they have the energy to carry huge amounts of fine material in suspension. On reaching the sea, the river current may suddenly be reduced, allowing the suspended material to be deposited. Overtime, this deposit builds up, reaching the surface. Much like braided channels, the river will start splitting up as it seeks the path of least resistance in shallow waters. These new streams never return to the main channel; therefore, they are called distributaries. Over many years, more and more load continues to be deposited at now the multiple mouths of the river, which means the delta continues to grow outwards. The land between the distributaries is usually marshy.

Question 80

Name and describe three types of deltas, giving examples of each. (go to word-doc ‘Rivers SUMMARY’ for diagrams to be able to draw in exam question)

Answer 80

1. River-dominated - river builds sharply out into ocean from coastline, sticks out (e.g. Mississippi)
2. Tide-dominated - tidal flow landward and seaward causes channels and islands perpendicular to coast (e.g. Ganges)
3. Wave-dominated - waves push sediment back onto coastline, very rounded and smoothed delta coming out of coastline (e.g. Nile)

Question 81

Name and explain factors increasing the risk of flooding

Answer 81

• Precipitation (duration and intensity): Heavy, prolonged rainfall means there will be more water than the drainage system can handle leading the lots of surface run-off (i.e. flooding)
• Impermeable rock: (e.g. granite, slate) The water from the river will go through the soil on top of the rocks but won’t be able to percolate, leading to large amounts of overlandflow (i.e. flooding)
• Saturated soils: Water won’t be able to infiltrate, leading to large amounts of overlandflow (i.e. flooding)
• Rapidly increasing temperatures in spring: The snow will melt at a very high rate and go into the river all at once, exceeding the river’s capacity, leading to flooding
• Urbanisation on the drainage basin: these consist largely of impermeable concrete, which encourages overland flow. Drains and sewers take water quickly and directly to the river channel. Houses with sloping roofs further increase the amount of run-off.
• Deforestation: trees and plants intercept precipitation (i.e. they catch or drink water). If there is little vegetation in the drainage basin, then surface run-off will be high.
• Drainage /Filling in Marshes: When it rains, the emptied swamps will quickly fill and flood
• Steep slopes: As soon as the rains falls it doesn’t have the time to infiltrate because it’s never still, racing down the slope
• Hard, dry soil: The water won’t be able to infiltrate, leading to large surface run-off
• Frozen Ground: The water won’t be able to infiltrate, leading to large surface run-off

Question 82

List different flood control methods, briefly explaining each

Answer 82

• Dams and Reservoirs – a wall in the river that controls by holding back the water (creating a reservoir) and allowing only a specific amount of water to flow past
• Afforestation – planting trees so that precipitation can be intercepts, decreasing amount of surface run-off
• Channelization/Stabilisation of the river banks and bed – lining the river bed and banks with concrete, increasing the velocity of the river, enabling the river to drain faster when the discharge increases
• Dredging – removing sediment at the bottom of a river/lake to allow for more capacity to hold water
• Flood relief/Diversionary spillways – Formation of streams leading off the main channel which can be filled with water at times of flood, relieving the main channel of excess discharge
• Land use planning – Planning where to build houses and infrastructure, so that these aren’t damaged in the event of a flood and/or they don’t increase the risk of flooding
• Flood levee – building an artificial levee (usually increasing the height of a natural one) so that the river can hold more water without flooding

Question 83

What are some of the opportunities presented by a river?

Answer 83

• Alluvial soils
• Hydroelectric power
• Trade and transport
• Water supply
  o Domestic
  o Irrigation
  o Industries (machines need to be cooled with water)
• Recreation/Tourism
• Fishing
• Natural Capital - money can be made from the opportunities that the river provides
• Waste disposal

Question 84

What are some of the hazards presented by a river?

Answer 84

- Flooding
o	Destruction of infrastructure
o	Disease
o	Death
o	Economic loss
- Human disruption
o	Loss of biodiversity
o	Dam collapse
o	Water pollution
o	Ocean dead zones at mouth

Question 85

When did the flooding of the Valency occur?

Answer 85

at 15:30 on August 16th, 2004

Question 86

What and where is Boscastle?

Answer 86

Boscastle is a small seaside tourist resort on the north coast of Cornwall, below Bodmin Moor

Question 87

How many cars and buildings were washed into the sea? (Valency flood)

Answer 87

80 cars and 6 buildings

Question 88

How many tonnes of sediment was moved downstream? (Valency flood)

Answer 88

20 tonnes

Question 89

How many people were rescued by how many helicopters? Did anyone die? (Valency flood

Answer 89

Over 100 people were rescued by 7 helicopters, with no fatalities

Question 90

How many properties were flooded? (Valency flood)

Answer 90

58

Question 91

How many people were affected by the Valency flood?

Answer 91

About 1000 residents and tourists were affected and had to leave and find temporary shelter

Question 92

What was the total cost of damage of the Valency flood?

Answer 92

£2 million

Question 93

What were the physical causes of the Valency flood?

Answer 93

• Heavy localized rain (9cm/h)
• Stormy weather prior to flood (saturated soils)
• Topography of the land – the landscape upstream Boscastle acts as a funnel, steep valley sides
• Narrow river channels in the village
• At a confluence (between the Valency and the Jordan), more water
• Much of the drainage basin is made of granite (impermeable rock)
• High tides held the river water back, flooding the coastal plains

Question 94

What were the human causes of the Valency flood?

Answer 94

• Boscastle built on a floodplain
• Several bridges, diverting the water out of the river
• Bodmin Moor has been deforested
• Bodmin Moor has been drained to enable the land to be used for grazing

Question 95

What action was taken to prevent such a flood occurring again? (Valency flood)

Answer 95

• Program of afforestation in Bodmin Moor
• Lowered and widened the river channel
• Raised carparks by about 1 metre
• Management of the drainage basin
• Recuperation of marshes