Chapter 8.-river Action: The Work Of Rivers

Question 1

What is the source

Answer 1

It is where the river begins

Question 2

What is the watershed

Answer 2

It is the lines dividing the waters of a river and its tributaries (River basin) from those of another river and its tributaries (another basin).

Question 3

What are tributaries

Answer 3

They are smaller rivers that join a larger river.

Question 4

What is a confluence

Answer 4

It is the place where a river tributary joins the main river

Question 5

What is an estuary

Answer 5

Its the tidal moth of a river

Question 6

What is a delta

Answer 6

The land that forms at the mouth of rivers

Question 7

What is the mouth

Answer 7

Where the river enters the sea or lake

Question 8

What is the course or a river

Answer 8

Its the path of the river from source to mouth

Question 9

What is the basin

Answer 9

Its the area drained by the river and its tributaries

Question 10

What are distributaries

Answer 10

They are small rivers that break off from the main river as it enters the sea

Question 11

Hat are the processes of river transportation

Answer 11

They are saltation, traction, suspension and solution.

Question 12

What is saltation

Answer 12

It is when small stones are bounced along the bed of a river.

Question 13

What is solution

Answer 13

Its when rock minerals are dissolved in the water and carried away.

Question 14

What is suspension

Answer 14

It is when light material such as silt is transported in the water.

Question 15

What is traction

Answer 15

Its when larger rocks are rolled along the river bed

Question 16

What is the old age stage

Answer 16

It is the last of the three stages of a river. In the old age stage the river slows down and meanders. It deposits its load either because the river is losing energy or because the load is too great.

Question 17

What are three landforms of the old age stage.

Answer 17

Three landforms of the old age stage are levees, deltas and ox-bow lakes

Question 18

What are 10 river features

Answer 18

10 river features are the source, watershed, tributaries, estuary, confluence, delta, mouth, distributaries, basin and the course.

Question 19

What is an ox-bow lake

Answer 19

Its a curved shape of water formed when a meander in a river is cut off, leaving the river to straighten its course.

E.g - the river Moy, co. Mayo

Question 20

How is an ox-bow lake formed

Answer 20

Its formed:
1.the river forms a meander

2. the river wears away (erodes) the land here on the outer bends
3. the river deposits on the inner bends
4. during a flood, the river breaks through to straighten its course
5. the meander is cut off by the river to form an ox-bow lake. Eventually the lake will dry out, leaving the shape of the old lake in the landscape.

Question 21

What is a levee

Answer 21

Its a raised bank of earth running along the sides of a river.

Question 22

How is a levee formed

Answer 22

Its formed when -
1.the river floods and covers the floodplain

2. the river deposits silt (sediment) on the floodplain as it slows down
3. the faster flowing water of the river channel comes in contact with the slower flowing water of the floodplain along the bank of the river, resulting in silt being deposited.
4. more silt is deposited along the bank than on the floodplain. This forms a raised bank called a levee.

Question 23

What is a delta

Answer 23

Its low lying sand that forms at the mouth of the river when they enter a lake or the sea.

Question 24

How is a delta formed

Answer 24

Its formed when -
1. The river slows down and enters the lake or sea and it deposits its load to build the delta.

2. The delta forms when the sea currents are not strong enough to remove the silt.
3. The river breaks up into distributaries (streams that branch iff from the main channel of the river).

E.g. The Nile , Egypt

Question 25

Give two causes of river flooding

Answer 25

Two causes of river flooding are
-poorly constructed bridges, weirs and failures to dredge the riverbed can all causes force the extra water out onto the land.

• increased house construction on the floodplain has also contributed to flooding risks.

Question 26

When is there usually flooding

Answer 26

Usually, there is flooding in the winter months and is often caused by extreme weather conditions, such as a no. of days of heavy rainfall. But the way people manage the rivers can also contribute to flooding.

Question 27

What are two effects of flooding

Answer 27

• There are deaths through drowning - e.g about 400 killed in Mississippi floods of 2011
• vast areas of farmland and cities covered by water - millions of Chinese effected by Yangtze floods of 2011 through evacuation and homes being destroyed

Question 28

What are dams

Answer 28

They are a barrier built to hold back the flow of a river. The main dams in Ireland were built for electricity. Also act as reservoirs to store water

Question 29

What are two advantages of dams

Answer 29

2 advantages of dams are
-hydroelectricity produced for homes and industry’s

• water stored for homes and industry as lake behind dam acts as reservoir.

Question 30

What are 2 disadvantages of dams

Answer 30

2 disadvantages of dams are
- good farmland flooded when lake behind dam is being made.

• danger posed for people who live downstream of the dam in case it collapses or overflows.