CHAPTER 1: RIVER ENVIRONMENTS

Question 1

Describe what is meant by the hydrological cycle.

Answer 1

This is the global circulation of water between the air, land and sea, and it is a giant closed system.

Question 2

Describe what is meant by a closed system in the hydrological cycle.

Answer 2

This means that there is a fixed amount of water because water neither enters nor leaves the Earth and its atmosphere.

Question 3

Describe the following major store - The Atmosphere.

Answer 3

The water exists either as water vapour or as minute droplets in clouds.

Question 4

Describe the following major store - The Land.

Answer 4

Water is stored on the surface in rivers, lakes and reservoirs. Water is taken in by plants and stored in vegetation for short periods of time. It is also stored below ground in the bedrock. This is known as the groundwater store (aquifer). Water mostly exists in these stores in a liquid form. However, it can also exist in a solid form as snow and ice, for example in ice sheets, glaciers and snowfields.

Question 5

Describe the following major store - The Sea.

Answer 5

It is estimated that over 95% of the Earth’s water is stored in the sea. This is mostly held in liquid form, but also as ice, for example the icebergs in high-latitude seas.

Question 6

While the amount of water in the global hydrological cycle cannot change, the proportion held in the different stores can. Explain how this can occur.

Answer 6

These variations are caused by changes in the Sun’s energy. For example, an increase in the Sun’s energy will lead to more evaporation and possibly to the melting of ice sheets and glaciers.

Question 7

Describe the following flow (transfer) - Evaporation.

Answer 7

The hydrological cycle starts with evaporation due to the heat of the Sun. Water is converted from a liquid into a gas called water vapour. This takes place from the surface of the sea and from water surfaces (ponds and lakes) on land. Evaporation is particularly important in the transfer of water from the sea store into the atmosphere.

Question 8

Describe the following flow (transfer) - Transpiration.

Answer 8

Plants take up liquid water from the soil and ‘breathe’ it into the atmosphere as water vapour.

Question 9

Describe the following flow (transfer) - Evapotranspiration.

Answer 9

The loss of moisture from the ground by direct evaporation from water bodies and the soil, plus transpiration from plants.

Question 10

Describe the following flow (transfer) - Condensation.

Answer 10

The change in the atmosphere when water vapour cools and becomes liquid. The liquid takes the form of water droplets that appear in the atmosphere as clouds.

Question 11

Describe the following flow (transfer) - Precipitation.

Answer 11

The transfer of water in any form (rain, hail or snow) from the atmosphere to the land or sea surface.

Question 12

Describe the following flow (transfer) - Overland Flow.

Answer 12

Most precipitation that hits the ground moves due to gravity and eventually enters a stream, river or lake. This is known as run off.

Question 13

Describe the following flow (transfer) - Infiltration and Percolation.

Answer 13

The transfer of water downwards through the soil and rock into the aquifer of groundwater store.

Question 14

Describe the following flow (transfer) - Throughflow.

Answer 14

This takes place between the ground surface and the top of the groundwater store. As a result of gravity, water moves slowly through the soil until it reaches a stream or river.

Question 15

Describe the following flow (transfer) - Groundwater Flow.

Answer 15

This happens in the rocks of the aquifer and is the underground transfer of water to rivers, lakes and the sea.

Question 16

Some of the water that falls as rain on the land may never reach the sea. Explain this.

Answer 16

Instead, it is returned directly back to the atmosphere from the land by the transpiration of plants and evaporation from both soil and water bodies.

Question 17

The main difference between the drainage basin and the hydrological cycle is that a drainage basin is an open system Describe what is meant by this.

Answer 17

A drainage basin has external inputs and output. The amount of water in the basin system varies over time. In the hydrological cycle the amount of water remains exactly the same.

Question 18

What are the inputs of a drainage basin?

Answer 18

• Energy from the Sun.
• Precipitation formed from moisture picked up outside the basin.
• Possibly water from tributary drainage basins.

Question 19

What are the outputs of a drainage basin?

Answer 19

• The River’s Discharge
• The water in its basin from which evaporation and transpiration take place; this water eventually falls as precipitation in another drainage basin.

Question 20

What is meant by the term, “Watershed”?

Answer 20

The boundary between neighboring drainage basins.

Question 21

What is meant by the term, “Confluence”?

Answer 21

Smaller streams, or tributaries, enter the main river channel at locations known as confluences.

Question 22

What is meant by the term, “Estuary”?

Answer 22

The mouth of the river where it flows out to the sea.

Question 23

Types of Drainage Basins.

Answer 23

• Those that simply collect and deliver water to the sea.
• Those that are parts of much larger drainage basins.
• Some drainage basins do not lead, either directly or indirectly, to
  the open sea. Rather they lead to ‘inland’ seas or lakes.

Question 24

Explain what a “Channel Network” is.

Answer 24

A channel (or drainage) network is the system of surface (streams and rivers) and underground channels that collects and transports the precipitation falling on the drainage basin.

Question 25

Measurements which can be taken from channel networks.

Answer 25

• Channel networks can be mapped
• The lengths of channel networks can be measured
• The densities (number of channels per unit area) can be measured

Question 26

Features of Drainage Basins

They determine how quickly or slowly water moves through the basin.

Answer 26

• Size
• Shape
• Rock Type
• Relief
• Land Use

Question 27

Those features can affect overland flow or run flow.

Answer 27

• Rock type and relief are physical factors over which people have
  little control.
• Land use can be easily changed by people.
• Woodland holds water and slows overland flow. However, once
  it is cleared for cultivation, run off will speed off.
• The built-up areas of towns and cities can speed up run off even
  more.
• Rainwater hits solid surfaces such as roofs, pavements and
  roads. It is then quickly channelled into drains which speed its
  delivery into a stream or river.

Question 28

Factors affecting Run off

Answer 28

Rapid run off - steep slopes; impermeable rock

Little run off - permeable rock; rivers have disappeared
underground

Woodland - slows rate of run off

Urban area - speeds up rate of run off